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 do
not yet exist.
Let's add a helper that extracts a field and caps the version to a
given value.
Signed-off-by: Andrew Murray <andrew.murray@xxxxxxx>
---
arch/arm64/include/asm/cpufeature.h | 16 ++++++++++++++++
1 file changed, 16 insertions(+)
diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 4261d55..1462fd1 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -447,6 +447,22 @@ cpuid_feature_extract_unsigned_field(u64 features, int field)
return cpuid_feature_extract_unsigned_field_width(features, field, 4);
}
+static inline u64 __attribute_const__
+cpuid_feature_cap_signed_field_width(u64 features, int field, int width,
+ s64 cap)
+{
+ s64 val = cpuid_feature_extract_signed_field_width(features, field,
+ width);
+ u64 mask = GENMASK_ULL(field + width - 1, field);
+
+ 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);
--
2.7.4
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