From: Andrew Murray andrew.murray@arm.com
commit 8e35aa642ee4dab01b16cc4b2df59d1936f3b3c2 upstream.
When emulating ID registers there is often a need to cap the version bits of a feature such that the guest will not use features that the host is not aware of. For example, when KVM mediates access to the PMU by emulating register accesses.
Let's add a helper that extracts a performance monitors ID field and caps the version to a given value.
Fields that identify the version of the Performance Monitors Extension do not follow the standard ID scheme, and instead follow the scheme described in ARM DDI 0487E.a page D13-2825 "Alternative ID scheme used for the Performance Monitors Extension version". The value 0xF means an IMPLEMENTATION DEFINED PMU is present, and values 0x0-OxE can be treated the same as an unsigned field with 0x0 meaning no PMU is present.
Signed-off-by: Andrew Murray andrew.murray@arm.com Reviewed-by: Suzuki K Poulose suzuki.poulose@arm.com [Mark: rework to handle perfmon fields] Signed-off-by: Mark Rutland mark.rutland@arm.com Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Zenghui Yu yuzenghui@huawei.com --- arch/arm64/include/asm/cpufeature.h | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h index 05f41d8f7db3..a3cc478d2570 100644 --- a/arch/arm64/include/asm/cpufeature.h +++ b/arch/arm64/include/asm/cpufeature.h @@ -422,6 +422,29 @@ cpuid_feature_extract_unsigned_field(u64 features, int field) return cpuid_feature_extract_unsigned_field_width(features, field, 4); }
+/* + * Fields that identify the version of the Performance Monitors Extension do + * not follow the standard ID scheme. See ARM DDI 0487E.a page D13-2825, + * "Alternative ID scheme used for the Performance Monitors Extension version". + */ +static inline u64 __attribute_const__ +cpuid_feature_cap_perfmon_field(u64 features, int field, u64 cap) +{ + u64 val = cpuid_feature_extract_unsigned_field(features, field); + u64 mask = GENMASK_ULL(field + 3, field); + + /* Treat IMPLEMENTATION DEFINED functionality as unimplemented */ + if (val == 0xf) + val = 0; + + if (val > cap) { + features &= ~mask; + features |= (cap << field) & mask; + } + + return features; +} + static inline u64 arm64_ftr_mask(const struct arm64_ftr_bits *ftrp) { return (u64)GENMASK(ftrp->shift + ftrp->width - 1, ftrp->shift);