To anyone who has played with FEAT_NV, it is obvious that the level
of performance is rather low due to the trap amplification that it
imposes on the host hypervisor. FEAT_NV2 solves a number of the
problems that FEAT_NV had.
It also turns out that all the existing hardware that has FEAT_NV
also has FEAT_NV2. Finally, it is now allowed by the architecture
to build FEAT_NV2 *only* (as denoted by ID_AA64MMFR4_EL1.NV_frac),
which effectively seals the fate of FEAT_NV.
Restrict the NV support to NV2, and be done with it. Nobody will
cry over the old crap.
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
---
arch/arm64/kernel/cpufeature.c | 22 +++++++++++++++-------
arch/arm64/tools/cpucaps | 2 ++
2 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 7dcda39537f8..95a677cf8c04 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -439,6 +439,7 @@ static const struct arm64_ftr_bits ftr_id_aa64mmfr3[] = {
static const struct arm64_ftr_bits ftr_id_aa64mmfr4[] = {
S_ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_LOWER_SAFE, ID_AA64MMFR4_EL1_E2H0_SHIFT, 4, 0),
+ ARM64_FTR_BITS(FTR_HIDDEN, FTR_STRICT, FTR_HIGHER_SAFE, ID_AA64MMFR4_EL1_NV_frac_SHIFT, 4, 0),
ARM64_FTR_END,
};
@@ -2080,12 +2081,8 @@ static bool has_nested_virt_support(const struct arm64_cpu_capabilities *cap,
if (kvm_get_mode() != KVM_MODE_NV)
return false;
- if (!has_cpuid_feature(cap, scope)) {
- pr_warn("unavailable: %s\n", cap->desc);
- return false;
- }
-
- return true;
+ return (__system_matches_cap(ARM64_HAS_NV2) |
+ __system_matches_cap(ARM64_HAS_NV2_ONLY));
}
static bool hvhe_possible(const struct arm64_cpu_capabilities *entry,
@@ -2391,12 +2388,23 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.matches = runs_at_el2,
.cpu_enable = cpu_copy_el2regs,
},
+ {
+ .capability = ARM64_HAS_NV2,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .matches = has_cpuid_feature,
+ ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, NV, NV2)
+ },
+ {
+ .capability = ARM64_HAS_NV2_ONLY,
+ .type = ARM64_CPUCAP_SYSTEM_FEATURE,
+ .matches = has_cpuid_feature,
+ ARM64_CPUID_FIELDS(ID_AA64MMFR4_EL1, NV_frac, NV2_ONLY)
+ },
{
.desc = "Nested Virtualization Support",
.capability = ARM64_HAS_NESTED_VIRT,
.type = ARM64_CPUCAP_SYSTEM_FEATURE,
.matches = has_nested_virt_support,
- ARM64_CPUID_FIELDS(ID_AA64MMFR2_EL1, NV, IMP)
},
{
.capability = ARM64_HAS_32BIT_EL0_DO_NOT_USE,
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index fea24bcd6252..480de648cd03 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -41,6 +41,8 @@ HAS_LSE_ATOMICS
HAS_MOPS
HAS_NESTED_VIRT
HAS_NO_HW_PREFETCH
+HAS_NV2
+HAS_NV2_ONLY
HAS_PAN
HAS_S1PIE
HAS_RAS_EXTN
--
2.39.2
