[PATCH v4 15/16] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available

[Shameer Kolothum]

From: Julien Grall <julien.gr...@arm.com>

At the moment, the function kvm_get_vmid_bits() is looking up for the
sanitized value of ID_AA64MMFR1_EL1 and extract the information
regarding the number of VMID bits supported.

This is fine as the function is mainly used during VMID roll-over. New
use in a follow-up patch will require the function to be called a every
context switch so we want the function to be more efficient.

A new capability is introduced to tell whether 16-bit VMID is
available.

Signed-off-by: Julien Grall <julien.gr...@arm.com>
---
 arch/arm64/include/asm/cpucaps.h | 3 ++-
 arch/arm64/include/asm/kvm_mmu.h | 4 +---
 arch/arm64/kernel/cpufeature.c   | 9 +++++++++
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
index c40f2490cd7b..acb92da5c254 100644
--- a/arch/arm64/include/asm/cpucaps.h
+++ b/arch/arm64/include/asm/cpucaps.h
@@ -67,7 +67,8 @@
 #define ARM64_HAS_LDAPR                                59
 #define ARM64_KVM_PROTECTED_MODE               60
 #define ARM64_WORKAROUND_NVIDIA_CARMEL_CNP     61
+#define ARM64_HAS_16BIT_VMID                   62
 
-#define ARM64_NCAPS                            62
+#define ARM64_NCAPS                            63
 
 #endif /* __ASM_CPUCAPS_H */
diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 90873851f677..c3080966ef83 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -213,9 +213,7 @@ void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool 
was_enabled);
 
 static inline unsigned int kvm_get_vmid_bits(void)
 {
-       int reg = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1);
-
-       return get_vmid_bits(reg);
+       return cpus_have_const_cap(ARM64_HAS_16BIT_VMID) ? 16 : 8;
 }
 
 /*
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index e5281e1c8f1d..ff956fb2f712 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2203,6 +2203,15 @@ static const struct arm64_cpu_capabilities 
arm64_features[] = {
                .matches = has_cpuid_feature,
                .min_field_value = 1,
        },
+       {
+               .capability = ARM64_HAS_16BIT_VMID,
+               .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+               .sys_reg = SYS_ID_AA64MMFR1_EL1,
+               .field_pos = ID_AA64MMFR1_VMIDBITS_SHIFT,
+               .sign = FTR_UNSIGNED,
+               .min_field_value = ID_AA64MMFR1_VMIDBITS_16,
+               .matches = has_cpuid_feature,
+       },
        {},
 };
 
-- 
2.17.1