drivers/lguest/x86/core.c

   1 /*
   2  * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation.
   3  * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI.
   4  *
   5  * This program is free software; you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation; either version 2 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful, but
  11  * WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
  13  * NON INFRINGEMENT.  See the GNU General Public License for more
  14  * details.
  15  *
  16  * You should have received a copy of the GNU General Public License
  17  * along with this program; if not, write to the Free Software
  18  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  19  */
  20 /*P:450 This file contains the x86-specific lguest code.  It used to be all
  21  * mixed in with drivers/lguest/core.c but several foolhardy code slashers
  22  * wrestled most of the dependencies out to here in preparation for porting
  23  * lguest to other architectures (see what I mean by foolhardy?).
  24  *
  25  * This also contains a couple of non-obvious setup and teardown pieces which
  26  * were implemented after days of debugging pain. :*/
  27 #include <linux/kernel.h>
  28 #include <linux/start_kernel.h>
  29 #include <linux/string.h>
  30 #include <linux/console.h>
  31 #include <linux/screen_info.h>
  32 #include <linux/irq.h>
  33 #include <linux/interrupt.h>
  34 #include <linux/clocksource.h>
  35 #include <linux/clockchips.h>
  36 #include <linux/cpu.h>
  37 #include <linux/lguest.h>
  38 #include <linux/lguest_launcher.h>
  39 #include <asm/paravirt.h>
  40 #include <asm/param.h>
  41 #include <asm/page.h>
  42 #include <asm/pgtable.h>
  43 #include <asm/desc.h>
  44 #include <asm/setup.h>
  45 #include <asm/lguest.h>
  46 #include <asm/uaccess.h>
  47 #include <asm/i387.h>
  48 #include "../lg.h"
  49
  50 static int cpu_had_pge;
  51
  52 static struct {
  53         unsigned long offset;
  54         unsigned short segment;
  55 } lguest_entry;
  56
  57 /* Offset from where switcher.S was compiled to where we've copied it */
  58 static unsigned long switcher_offset(void)
  59 {
  60         return SWITCHER_ADDR - (unsigned long)start_switcher_text;
  61 }
  62
  63 /* This cpu's struct lguest_pages. */
  64 static struct lguest_pages *lguest_pages(unsigned int cpu)
  65 {
  66         return &(((struct lguest_pages *)
  67                   (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]);
  68 }
  69
  70 static DEFINE_PER_CPU(struct lg_cpu *, last_cpu);
  71
  72 /*S:010
  73  * We approach the Switcher.
  74  *
  75  * Remember that each CPU has two pages which are visible to the Guest when it
  76  * runs on that CPU.  This has to contain the state for that Guest: we copy the
  77  * state in just before we run the Guest.
  78  *
  79  * Each Guest has "changed" flags which indicate what has changed in the Guest
  80  * since it last ran.  We saw this set in interrupts_and_traps.c and
  81  * segments.c.
  82  */
  83 static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages)
  84 {
  85         /* Copying all this data can be quite expensive.  We usually run the
  86          * same Guest we ran last time (and that Guest hasn't run anywhere else
  87          * meanwhile).  If that's not the case, we pretend everything in the
  88          * Guest has changed. */
  89         if (__get_cpu_var(last_cpu) != cpu || cpu->last_pages != pages) {
  90                 __get_cpu_var(last_cpu) = cpu;
  91                 cpu->last_pages = pages;
  92                 cpu->changed = CHANGED_ALL;
  93         }
  94
  95         /* These copies are pretty cheap, so we do them unconditionally: */
  96         /* Save the current Host top-level page directory. */
  97         pages->state.host_cr3 = __pa(current->mm->pgd);
  98         /* Set up the Guest's page tables to see this CPU's pages (and no
  99          * other CPU's pages). */
 100         map_switcher_in_guest(cpu, pages);
 101         /* Set up the two "TSS" members which tell the CPU what stack to use
 102          * for traps which do directly into the Guest (ie. traps at privilege
 103          * level 1). */
 104         pages->state.guest_tss.sp1 = cpu->esp1;
 105         pages->state.guest_tss.ss1 = cpu->ss1;
 106
 107         /* Copy direct-to-Guest trap entries. */
 108         if (cpu->changed & CHANGED_IDT)
 109                 copy_traps(cpu, pages->state.guest_idt, default_idt_entries);
 110
 111         /* Copy all GDT entries which the Guest can change. */
 112         if (cpu->changed & CHANGED_GDT)
 113                 copy_gdt(cpu, pages->state.guest_gdt);
 114         /* If only the TLS entries have changed, copy them. */
 115         else if (cpu->changed & CHANGED_GDT_TLS)
 116                 copy_gdt_tls(cpu, pages->state.guest_gdt);
 117
 118         /* Mark the Guest as unchanged for next time. */
 119         cpu->changed = 0;
 120 }
 121
 122 /* Finally: the code to actually call into the Switcher to run the Guest. */
 123 static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages)
 124 {
 125         /* This is a dummy value we need for GCC's sake. */
 126         unsigned int clobber;
 127
 128         /* Copy the guest-specific information into this CPU's "struct
 129          * lguest_pages". */
 130         copy_in_guest_info(cpu, pages);
 131
 132         /* Set the trap number to 256 (impossible value).  If we fault while
 133          * switching to the Guest (bad segment registers or bug), this will
 134          * cause us to abort the Guest. */
 135         cpu->regs->trapnum = 256;
 136
 137         /* Now: we push the "eflags" register on the stack, then do an "lcall".
 138          * This is how we change from using the kernel code segment to using
 139          * the dedicated lguest code segment, as well as jumping into the
 140          * Switcher.
 141          *
 142          * The lcall also pushes the old code segment (KERNEL_CS) onto the
 143          * stack, then the address of this call.  This stack layout happens to
 144          * exactly match the stack layout created by an interrupt... */
 145         asm volatile("pushf; lcall *lguest_entry"
 146                      /* This is how we tell GCC that %eax ("a") and %ebx ("b")
 147                       * are changed by this routine.  The "=" means output. */
 148                      : "=a"(clobber), "=b"(clobber)
 149                      /* %eax contains the pages pointer.  ("0" refers to the
 150                       * 0-th argument above, ie "a").  %ebx contains the
 151                       * physical address of the Guest's top-level page
 152                       * directory. */
 153                      : "0"(pages), "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir))
 154                      /* We tell gcc that all these registers could change,
 155                       * which means we don't have to save and restore them in
 156                       * the Switcher. */
 157                      : "memory", "%edx", "%ecx", "%edi", "%esi");
 158 }
 159 /*:*/
 160
 161 /*M:002 There are hooks in the scheduler which we can register to tell when we
 162  * get kicked off the CPU (preempt_notifier_register()).  This would allow us
 163  * to lazily disable SYSENTER which would regain some performance, and should
 164  * also simplify copy_in_guest_info().  Note that we'd still need to restore
 165  * things when we exit to Launcher userspace, but that's fairly easy.
 166  *
 167  * We could also try using this hooks for PGE, but that might be too expensive.
 168  *
 169  * The hooks were designed for KVM, but we can also put them to good use. :*/
 170
 171 /*H:040 This is the i386-specific code to setup and run the Guest.  Interrupts
 172  * are disabled: we own the CPU. */
 173 void lguest_arch_run_guest(struct lg_cpu *cpu)
 174 {
 175         /* Remember the awfully-named TS bit?  If the Guest has asked to set it
 176          * we set it now, so we can trap and pass that trap to the Guest if it
 177          * uses the FPU. */
 178         if (cpu->ts)
 179                 unlazy_fpu(current);
 180
 181         /* SYSENTER is an optimized way of doing system calls.  We can't allow
 182          * it because it always jumps to privilege level 0.  A normal Guest
 183          * won't try it because we don't advertise it in CPUID, but a malicious
 184          * Guest (or malicious Guest userspace program) could, so we tell the
 185          * CPU to disable it before running the Guest. */
 186         if (boot_cpu_has(X86_FEATURE_SEP))
 187                 wrmsr(MSR_IA32_SYSENTER_CS, 0, 0);
 188
 189         /* Now we actually run the Guest.  It will return when something
 190          * interesting happens, and we can examine its registers to see what it
 191          * was doing. */
 192         run_guest_once(cpu, lguest_pages(raw_smp_processor_id()));
 193
 194         /* Note that the "regs" structure contains two extra entries which are
 195          * not really registers: a trap number which says what interrupt or
 196          * trap made the switcher code come back, and an error code which some
 197          * traps set.  */
 198
 199          /* Restore SYSENTER if it's supposed to be on. */
 200          if (boot_cpu_has(X86_FEATURE_SEP))
 201                 wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0);
 202
 203         /* If the Guest page faulted, then the cr2 register will tell us the
 204          * bad virtual address.  We have to grab this now, because once we
 205          * re-enable interrupts an interrupt could fault and thus overwrite
 206          * cr2, or we could even move off to a different CPU. */
 207         if (cpu->regs->trapnum == 14)
 208                 cpu->arch.last_pagefault = read_cr2();
 209         /* Similarly, if we took a trap because the Guest used the FPU,
 210          * we have to restore the FPU it expects to see.
 211          * math_state_restore() may sleep and we may even move off to
 212          * a different CPU. So all the critical stuff should be done
 213          * before this.  */
 214         else if (cpu->regs->trapnum == 7)
 215                 math_state_restore();
 216 }
 217
 218 /*H:130 Now we've examined the hypercall code; our Guest can make requests.
 219  * Our Guest is usually so well behaved; it never tries to do things it isn't
 220  * allowed to, and uses hypercalls instead.  Unfortunately, Linux's paravirtual
 221  * infrastructure isn't quite complete, because it doesn't contain replacements
 222  * for the Intel I/O instructions.  As a result, the Guest sometimes fumbles
 223  * across one during the boot process as it probes for various things which are
 224  * usually attached to a PC.
 225  *
 226  * When the Guest uses one of these instructions, we get a trap (General
 227  * Protection Fault) and come here.  We see if it's one of those troublesome
 228  * instructions and skip over it.  We return true if we did. */
 229 static int emulate_insn(struct lg_cpu *cpu)
 230 {
 231         u8 insn;
 232         unsigned int insnlen = 0, in = 0, shift = 0;
 233         /* The eip contains the *virtual* address of the Guest's instruction:
 234          * guest_pa just subtracts the Guest's page_offset. */
 235         unsigned long physaddr = guest_pa(cpu, cpu->regs->eip);
 236
 237         /* This must be the Guest kernel trying to do something, not userspace!
 238          * The bottom two bits of the CS segment register are the privilege
 239          * level. */
 240         if ((cpu->regs->cs & 3) != GUEST_PL)
 241                 return 0;
 242
 243         /* Decoding x86 instructions is icky. */
 244         insn = lgread(cpu, physaddr, u8);
 245
 246         /* 0x66 is an "operand prefix".  It means it's using the upper 16 bits
 247            of the eax register. */
 248         if (insn == 0x66) {
 249                 shift = 16;
 250                 /* The instruction is 1 byte so far, read the next byte. */
 251                 insnlen = 1;
 252                 insn = lgread(cpu, physaddr + insnlen, u8);
 253         }
 254
 255         /* We can ignore the lower bit for the moment and decode the 4 opcodes
 256          * we need to emulate. */
 257         switch (insn & 0xFE) {
 258         case 0xE4: /* in     <next byte>,%al */
 259                 insnlen += 2;
 260                 in = 1;
 261                 break;
 262         case 0xEC: /* in     (%dx),%al */
 263                 insnlen += 1;
 264                 in = 1;
 265                 break;
 266         case 0xE6: /* out    %al,<next byte> */
 267                 insnlen += 2;
 268                 break;
 269         case 0xEE: /* out    %al,(%dx) */
 270                 insnlen += 1;
 271                 break;
 272         default:
 273                 /* OK, we don't know what this is, can't emulate. */
 274                 return 0;
 275         }
 276
 277         /* If it was an "IN" instruction, they expect the result to be read
 278          * into %eax, so we change %eax.  We always return all-ones, which
 279          * traditionally means "there's nothing there". */
 280         if (in) {
 281                 /* Lower bit tells is whether it's a 16 or 32 bit access */
 282                 if (insn & 0x1)
 283                         cpu->regs->eax = 0xFFFFFFFF;
 284                 else
 285                         cpu->regs->eax |= (0xFFFF << shift);
 286         }
 287         /* Finally, we've "done" the instruction, so move past it. */
 288         cpu->regs->eip += insnlen;
 289         /* Success! */
 290         return 1;
 291 }
 292
 293 /*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */
 294 void lguest_arch_handle_trap(struct lg_cpu *cpu)
 295 {
 296         switch (cpu->regs->trapnum) {
 297         case 13: /* We've intercepted a General Protection Fault. */
 298                 /* Check if this was one of those annoying IN or OUT
 299                  * instructions which we need to emulate.  If so, we just go
 300                  * back into the Guest after we've done it. */
 301                 if (cpu->regs->errcode == 0) {
 302                         if (emulate_insn(cpu))
 303                                 return;
 304                 }
 305                 break;
 306         case 14: /* We've intercepted a Page Fault. */
 307                 /* The Guest accessed a virtual address that wasn't mapped.
 308                  * This happens a lot: we don't actually set up most of the page
 309                  * tables for the Guest at all when we start: as it runs it asks
 310                  * for more and more, and we set them up as required. In this
 311                  * case, we don't even tell the Guest that the fault happened.
 312                  *
 313                  * The errcode tells whether this was a read or a write, and
 314                  * whether kernel or userspace code. */
 315                 if (demand_page(cpu, cpu->arch.last_pagefault,
 316                                 cpu->regs->errcode))
 317                         return;
 318
 319                 /* OK, it's really not there (or not OK): the Guest needs to
 320                  * know.  We write out the cr2 value so it knows where the
 321                  * fault occurred.
 322                  *
 323                  * Note that if the Guest were really messed up, this could
 324                  * happen before it's done the LHCALL_LGUEST_INIT hypercall, so
 325                  * lg->lguest_data could be NULL */
 326                 if (cpu->lg->lguest_data &&
 327                     put_user(cpu->arch.last_pagefault,
 328                              &cpu->lg->lguest_data->cr2))
 329                         kill_guest(cpu, "Writing cr2");
 330                 break;
 331         case 7: /* We've intercepted a Device Not Available fault. */
 332                 /* If the Guest doesn't want to know, we already restored the
 333                  * Floating Point Unit, so we just continue without telling
 334                  * it. */
 335                 if (!cpu->ts)
 336                         return;
 337                 break;
 338         case 32 ... 255:
 339                 /* These values mean a real interrupt occurred, in which case
 340                  * the Host handler has already been run.  We just do a
 341                  * friendly check if another process should now be run, then
 342                  * return to run the Guest again */
 343                 cond_resched();
 344                 return;
 345         case LGUEST_TRAP_ENTRY:
 346                 /* Our 'struct hcall_args' maps directly over our regs: we set
 347                  * up the pointer now to indicate a hypercall is pending. */
 348                 cpu->hcall = (struct hcall_args *)cpu->regs;
 349                 return;
 350         }
 351
 352         /* We didn't handle the trap, so it needs to go to the Guest. */
 353         if (!deliver_trap(cpu, cpu->regs->trapnum))
 354                 /* If the Guest doesn't have a handler (either it hasn't
 355                  * registered any yet, or it's one of the faults we don't let
 356                  * it handle), it dies with this cryptic error message. */
 357                 kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)",
 358                            cpu->regs->trapnum, cpu->regs->eip,
 359                            cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault
 360                            : cpu->regs->errcode);
 361 }
 362
 363 /* Now we can look at each of the routines this calls, in increasing order of
 364  * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(),
 365  * deliver_trap() and demand_page().  After all those, we'll be ready to
 366  * examine the Switcher, and our philosophical understanding of the Host/Guest
 367  * duality will be complete. :*/
 368 static void adjust_pge(void *on)
 369 {
 370         if (on)
 371                 write_cr4(read_cr4() | X86_CR4_PGE);
 372         else
 373                 write_cr4(read_cr4() & ~X86_CR4_PGE);
 374 }
 375
 376 /*H:020 Now the Switcher is mapped and every thing else is ready, we need to do
 377  * some more i386-specific initialization. */
 378 void __init lguest_arch_host_init(void)
 379 {
 380         int i;
 381
 382         /* Most of the i386/switcher.S doesn't care that it's been moved; on
 383          * Intel, jumps are relative, and it doesn't access any references to
 384          * external code or data.
 385          *
 386          * The only exception is the interrupt handlers in switcher.S: their
 387          * addresses are placed in a table (default_idt_entries), so we need to
 388          * update the table with the new addresses.  switcher_offset() is a
 389          * convenience function which returns the distance between the
 390          * compiled-in switcher code and the high-mapped copy we just made. */
 391         for (i = 0; i < IDT_ENTRIES; i++)
 392                 default_idt_entries[i] += switcher_offset();
 393
 394         /*
 395          * Set up the Switcher's per-cpu areas.
 396          *
 397          * Each CPU gets two pages of its own within the high-mapped region
 398          * (aka. "struct lguest_pages").  Much of this can be initialized now,
 399          * but some depends on what Guest we are running (which is set up in
 400          * copy_in_guest_info()).
 401          */
 402         for_each_possible_cpu(i) {
 403                 /* lguest_pages() returns this CPU's two pages. */
 404                 struct lguest_pages *pages = lguest_pages(i);
 405                 /* This is a convenience pointer to make the code fit one
 406                  * statement to a line. */
 407                 struct lguest_ro_state *state = &pages->state;
 408
 409                 /* The Global Descriptor Table: the Host has a different one
 410                  * for each CPU.  We keep a descriptor for the GDT which says
 411                  * where it is and how big it is (the size is actually the last
 412                  * byte, not the size, hence the "-1"). */
 413                 state->host_gdt_desc.size = GDT_SIZE-1;
 414                 state->host_gdt_desc.address = (long)get_cpu_gdt_table(i);
 415
 416                 /* All CPUs on the Host use the same Interrupt Descriptor
 417                  * Table, so we just use store_idt(), which gets this CPU's IDT
 418                  * descriptor. */
 419                 store_idt(&state->host_idt_desc);
 420
 421                 /* The descriptors for the Guest's GDT and IDT can be filled
 422                  * out now, too.  We copy the GDT & IDT into ->guest_gdt and
 423                  * ->guest_idt before actually running the Guest. */
 424                 state->guest_idt_desc.size = sizeof(state->guest_idt)-1;
 425                 state->guest_idt_desc.address = (long)&state->guest_idt;
 426                 state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1;
 427                 state->guest_gdt_desc.address = (long)&state->guest_gdt;
 428
 429                 /* We know where we want the stack to be when the Guest enters
 430                  * the Switcher: in pages->regs.  The stack grows upwards, so
 431                  * we start it at the end of that structure. */
 432                 state->guest_tss.sp0 = (long)(&pages->regs + 1);
 433                 /* And this is the GDT entry to use for the stack: we keep a
 434                  * couple of special LGUEST entries. */
 435                 state->guest_tss.ss0 = LGUEST_DS;
 436
 437                 /* x86 can have a finegrained bitmap which indicates what I/O
 438                  * ports the process can use.  We set it to the end of our
 439                  * structure, meaning "none". */
 440                 state->guest_tss.io_bitmap_base = sizeof(state->guest_tss);
 441
 442                 /* Some GDT entries are the same across all Guests, so we can
 443                  * set them up now. */
 444                 setup_default_gdt_entries(state);
 445                 /* Most IDT entries are the same for all Guests, too.*/
 446                 setup_default_idt_entries(state, default_idt_entries);
 447
 448                 /* The Host needs to be able to use the LGUEST segments on this
 449                  * CPU, too, so put them in the Host GDT. */
 450                 get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT;
 451                 get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT;
 452         }
 453
 454         /* In the Switcher, we want the %cs segment register to use the
 455          * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so
 456          * it will be undisturbed when we switch.  To change %cs and jump we
 457          * need this structure to feed to Intel's "lcall" instruction. */
 458         lguest_entry.offset = (long)switch_to_guest + switcher_offset();
 459         lguest_entry.segment = LGUEST_CS;
 460
 461         /* Finally, we need to turn off "Page Global Enable".  PGE is an
 462          * optimization where page table entries are specially marked to show
 463          * they never change.  The Host kernel marks all the kernel pages this
 464          * way because it's always present, even when userspace is running.
 465          *
 466          * Lguest breaks this: unbeknownst to the rest of the Host kernel, we
 467          * switch to the Guest kernel.  If you don't disable this on all CPUs,
 468          * you'll get really weird bugs that you'll chase for two days.
 469          *
 470          * I used to turn PGE off every time we switched to the Guest and back
 471          * on when we return, but that slowed the Switcher down noticibly. */
 472
 473         /* We don't need the complexity of CPUs coming and going while we're
 474          * doing this. */
 475         get_online_cpus();
 476         if (cpu_has_pge) { /* We have a broader idea of "global". */
 477                 /* Remember that this was originally set (for cleanup). */
 478                 cpu_had_pge = 1;
 479                 /* adjust_pge is a helper function which sets or unsets the PGE
 480                  * bit on its CPU, depending on the argument (0 == unset). */
 481                 on_each_cpu(adjust_pge, (void *)0, 1);
 482                 /* Turn off the feature in the global feature set. */
 483                 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
 484         }
 485         put_online_cpus();
 486 };
 487 /*:*/
 488
 489 void __exit lguest_arch_host_fini(void)
 490 {
 491         /* If we had PGE before we started, turn it back on now. */
 492         get_online_cpus();
 493         if (cpu_had_pge) {
 494                 set_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE);
 495                 /* adjust_pge's argument "1" means set PGE. */
 496                 on_each_cpu(adjust_pge, (void *)1, 1);
 497         }
 498         put_online_cpus();
 499 }
 500
 501
 502 /*H:122 The i386-specific hypercalls simply farm out to the right functions. */
 503 int lguest_arch_do_hcall(struct lg_cpu *cpu, struct hcall_args *args)
 504 {
 505         switch (args->arg0) {
 506         case LHCALL_LOAD_GDT:
 507                 load_guest_gdt(cpu, args->arg1, args->arg2);
 508                 break;
 509         case LHCALL_LOAD_IDT_ENTRY:
 510                 load_guest_idt_entry(cpu, args->arg1, args->arg2, args->arg3);
 511                 break;
 512         case LHCALL_LOAD_TLS:
 513                 guest_load_tls(cpu, args->arg1);
 514                 break;
 515         default:
 516                 /* Bad Guest.  Bad! */
 517                 return -EIO;
 518         }
 519         return 0;
 520 }
 521
 522 /*H:126 i386-specific hypercall initialization: */
 523 int lguest_arch_init_hypercalls(struct lg_cpu *cpu)
 524 {
 525         u32 tsc_speed;
 526
 527         /* The pointer to the Guest's "struct lguest_data" is the only argument.
 528          * We check that address now. */
 529         if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1,
 530                                sizeof(*cpu->lg->lguest_data)))
 531                 return -EFAULT;
 532
 533         /* Having checked it, we simply set lg->lguest_data to point straight
 534          * into the Launcher's memory at the right place and then use
 535          * copy_to_user/from_user from now on, instead of lgread/write.  I put
 536          * this in to show that I'm not immune to writing stupid
 537          * optimizations. */
 538         cpu->lg->lguest_data = cpu->lg->mem_base + cpu->hcall->arg1;
 539
 540         /* We insist that the Time Stamp Counter exist and doesn't change with
 541          * cpu frequency.  Some devious chip manufacturers decided that TSC
 542          * changes could be handled in software.  I decided that time going
 543          * backwards might be good for benchmarks, but it's bad for users.
 544          *
 545          * We also insist that the TSC be stable: the kernel detects unreliable
 546          * TSCs for its own purposes, and we use that here. */
 547         if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable())
 548                 tsc_speed = tsc_khz;
 549         else
 550                 tsc_speed = 0;
 551         if (put_user(tsc_speed, &cpu->lg->lguest_data->tsc_khz))
 552                 return -EFAULT;
 553
 554         /* The interrupt code might not like the system call vector. */
 555         if (!check_syscall_vector(cpu->lg))
 556                 kill_guest(cpu, "bad syscall vector");
 557
 558         return 0;
 559 }
 560 /*:*/
 561
 562 /*L:030 lguest_arch_setup_regs()
 563  *
 564  * Most of the Guest's registers are left alone: we used get_zeroed_page() to
 565  * allocate the structure, so they will be 0. */
 566 void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start)
 567 {
 568         struct lguest_regs *regs = cpu->regs;
 569
 570         /* There are four "segment" registers which the Guest needs to boot:
 571          * The "code segment" register (cs) refers to the kernel code segment
 572          * __KERNEL_CS, and the "data", "extra" and "stack" segment registers
 573          * refer to the kernel data segment __KERNEL_DS.
 574          *
 575          * The privilege level is packed into the lower bits.  The Guest runs
 576          * at privilege level 1 (GUEST_PL).*/
 577         regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL;
 578         regs->cs = __KERNEL_CS|GUEST_PL;
 579
 580         /* The "eflags" register contains miscellaneous flags.  Bit 1 (0x002)
 581          * is supposed to always be "1".  Bit 9 (0x200) controls whether
 582          * interrupts are enabled.  We always leave interrupts enabled while
 583          * running the Guest. */
 584         regs->eflags = X86_EFLAGS_IF | 0x2;
 585
 586         /* The "Extended Instruction Pointer" register says where the Guest is
 587          * running. */
 588         regs->eip = start;
 589
 590         /* %esi points to our boot information, at physical address 0, so don't
 591          * touch it. */
 592
 593         /* There are a couple of GDT entries the Guest expects when first
 594          * booting. */
 595         setup_guest_gdt(cpu);
 596 }