[v12,1/4] arm64: cpufeature: introduce helper cpu_has_hw_af()
diff mbox series

Message ID 20191011140939.6115-2-justin.he@arm.com
State In Next
Commit 47d7b15b88f96a90694cfc607d0717d62dff6c45
Headers show
  • fix double page fault in cow_user_page for pfn mapping
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Commit Message

Jia He Oct. 11, 2019, 2:09 p.m. UTC
We unconditionally set the HW_AFDBM capability and only enable it on
CPUs which really have the feature. But sometimes we need to know
whether this cpu has the capability of HW AF. So decouple AF from
DBM by a new helper cpu_has_hw_af().

If later we noticed a potential performance issue on this path, we can
turn it into a static label as with other CPU features.

Signed-off-by: Jia He <justin.he@arm.com>
Suggested-by: Suzuki Poulose <Suzuki.Poulose@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
 arch/arm64/include/asm/cpufeature.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

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diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9cde5d2e768f..4261d55e8506 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -659,6 +659,20 @@  static inline u32 id_aa64mmfr0_parange_to_phys_shift(int parange)
 	default: return CONFIG_ARM64_PA_BITS;
+/* Check whether hardware update of the Access flag is supported */
+static inline bool cpu_has_hw_af(void)
+	u64 mmfr1;
+		return false;
+	mmfr1 = read_cpuid(ID_AA64MMFR1_EL1);
+	return cpuid_feature_extract_unsigned_field(mmfr1,
 #endif /* __ASSEMBLY__ */