arm64: cpufeature: Add read_cpuid_with_overrides()

__cpuinfo_store_cpu() stores the ID registers raw. Its gates on reading
a feature's register test those raw values. The exception is
gmid_el1_accessible(), which open-codes MTE's command-line override. It
checks the override with arm64_ftr_safe_value(), since
init_cpu_features() hasn't yet removed an unsafe one. The other gates
still read a feature's register when the command line disabled it. That's
the read that trapped on GMID_EL1.

Add read_cpuid_with_overrides(), which applies every valid override to
any register in arm64_ftr_regs[]. An override is valid when
arm64_ftr_safe_value() returns it unchanged. validate_ftr_regs() has
checked the table by the first store, so the lookup is safe there.
arm64_apply_feature_override() can't do this: it takes one field and no
descriptor to check the override against.

Store ID_AA64PFR1_EL1 through it, and replace gmid_el1_accessible()
with a test on the stored value at its three callers, as for SME.

Other readers of the stored value see the override too. With
arm64.nosme, __cpuinfo_store_cpu() no longer reads SMIDR_EL1. CPUs that
differ only in an ID_AA64PFR1_EL1 field the command line turned off no
longer taint the kernel. init_cpu_ftr_reg() logs a valid override as
"already set" rather than "forced".

The helper is Suzuki's override_cpu_ftr_reg(), without its other two
call sites.

Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Suggested-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/all/afc5bd00-28ca-413b-b047-ee53589c285d@arm.com/
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Signed-off-by: Will Deacon <will@kernel.org>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Jinjie Ruan <ruanjinjie@huawei.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

0 files changed, 0 insertions, 0 deletions