target/ppc: add user read/write functions for MMCR0

target/ppc: add user read/write functions for MMCR0

Userspace need access to PMU SPRs to be able to operate the PMU. One of
such SPRs is MMCR0.

MMCR0, as defined by PowerISA v3.1, is classified as a 'group A' PMU
register. This class of registers has common read/write rules that are
governed by MMCR0 PMCC bits. MMCR0 is also not fully exposed to problem
state: only MMCR0_FC, MMCR0_PMAO and MMCR0_PMAE bits are
readable/writable in this case.

This patch exposes MMCR0 to userspace by doing the following:

- two new callbacks, spr_read_MMCR0_ureg() and spr_write_MMCR0_ureg(),
are added to be used as problem state read/write callbacks of UMMCR0.
Both callbacks filters the amount of bits userspace is able to
read/write by using a MMCR0_UREG_MASK;

- problem state access control is done by the spr_groupA_read_allowed()
and spr_groupA_write_allowed() helpers. These helpers will read the
current PMCC bits from DisasContext and check whether the read/write
MMCR0 operation is valid or noti;

- to avoid putting exclusive PMU logic into the already loaded
translate.c file, let's create a new 'power8-pmu-regs.c.inc' file that
will hold all the spr_read/spr_write functions of PMU registers.

The 'power8' name of this new file intends to hint about the proven
support of the PMU logic to be added. The code has been tested with the
IBM POWER chip family, POWER8 being the oldest version tested. This
doesn't mean that the PMU logic will break with any other PPC64 chip
that implements Book3s, but rather that we can't assert that it works
properly with any Book3s compliant chip.

CC: Gustavo Romero <gustavo.romero@linaro.org>
Signed-off-by: Gustavo Romero <gromero@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Message-Id: <20211018010133.315842-3-danielhb413@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>