[PATCH v2 1/3] arch/arm64: Introduce a capability to tell whether 16-bit VMID is available

Shameer Kolothum
2021-06-16T15:57:56Z

From: Julien Grall <julien.grall@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.grall@arm.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
---
arch/arm64/include/asm/kvm_mmu.h | 4 +---
arch/arm64/kernel/cpufeature.c | 9 +++++++++
arch/arm64/tools/cpucaps | 1 +
3 files changed, 11 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 25ed956f9af1..2abdea7dcb43 100644
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -223,9 +223,7 @@ 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 efed2830d141..0642ebe118b0 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2218,6 +2218,15 @@ 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,
+ },
{},
};

diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index 21fbdda7086e..456b4cf1ba27 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -3,6 +3,7 @@
# Internal CPU capabilities constants, keep this list sorted

BTI
+HAS_16BIT_VMID
HAS_32BIT_EL0
HAS_32BIT_EL1
HAS_ADDRESS_AUTH
--
2.17.1