diff options
| author | Oliver Upton <oliver.upton@linux.dev> | 2025-09-24 16:51:50 -0700 |
|---|---|---|
| committer | Marc Zyngier <maz@kernel.org> | 2025-10-13 14:44:37 +0100 |
| commit | e0b5a7967dec05144bc98125f98c47f74fd1152b (patch) | |
| tree | 9c1df0ba5c219a83fe15faec1d9c30a7b119523c | |
| parent | fb10ddf35c1cc3b2888a944c0a3b1aa3baea585e (diff) | |
KVM: arm64: nv: Use FGT write trap of MDSCR_EL1 when available
Marc reports that the performance of running an L3 guest has regressed
by 60% as a result of setting MDCR_EL2.TDA to hide bad architecture.
That's of course terrible for the single user of recursive NV ;-)
While there's nothing to be done on non-FGT systems, take advantage of
the precise write trap of MDSCR_EL1 and leave the rest of the debug
registers untrapped.
Reported-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
| -rw-r--r-- | arch/arm64/kvm/config.c | 10 | ||||
| -rw-r--r-- | arch/arm64/kvm/nested.c | 9 |
2 files changed, 15 insertions, 4 deletions
diff --git a/arch/arm64/kvm/config.c b/arch/arm64/kvm/config.c index b1cf7660efe1..24bb3f36e9d5 100644 --- a/arch/arm64/kvm/config.c +++ b/arch/arm64/kvm/config.c @@ -1489,6 +1489,14 @@ static void __compute_hfgwtr(struct kvm_vcpu *vcpu) *vcpu_fgt(vcpu, HFGWTR_EL2) |= HFGWTR_EL2_TCR_EL1; } +static void __compute_hdfgwtr(struct kvm_vcpu *vcpu) +{ + __compute_fgt(vcpu, HDFGWTR_EL2); + + if (is_hyp_ctxt(vcpu)) + *vcpu_fgt(vcpu, HDFGWTR_EL2) |= HDFGWTR_EL2_MDSCR_EL1; +} + void kvm_vcpu_load_fgt(struct kvm_vcpu *vcpu) { if (!cpus_have_final_cap(ARM64_HAS_FGT)) @@ -1498,7 +1506,7 @@ void kvm_vcpu_load_fgt(struct kvm_vcpu *vcpu) __compute_hfgwtr(vcpu); __compute_fgt(vcpu, HFGITR_EL2); __compute_fgt(vcpu, HDFGRTR_EL2); - __compute_fgt(vcpu, HDFGWTR_EL2); + __compute_hdfgwtr(vcpu); __compute_fgt(vcpu, HAFGRTR_EL2); if (!cpus_have_final_cap(ARM64_HAS_FGT2)) diff --git a/arch/arm64/kvm/nested.c b/arch/arm64/kvm/nested.c index 7a045cad6bdf..f04cda40545b 100644 --- a/arch/arm64/kvm/nested.c +++ b/arch/arm64/kvm/nested.c @@ -1859,13 +1859,16 @@ void kvm_nested_setup_mdcr_el2(struct kvm_vcpu *vcpu) { u64 guest_mdcr = __vcpu_sys_reg(vcpu, MDCR_EL2); + if (is_nested_ctxt(vcpu)) + vcpu->arch.mdcr_el2 |= (guest_mdcr & NV_MDCR_GUEST_INCLUDE); /* * In yet another example where FEAT_NV2 is fscking broken, accesses * to MDSCR_EL1 are redirected to the VNCR despite having an effect * at EL2. Use a big hammer to apply sanity. + * + * Unless of course we have FEAT_FGT, in which case we can precisely + * trap MDSCR_EL1. */ - if (is_hyp_ctxt(vcpu)) + else if (!cpus_have_final_cap(ARM64_HAS_FGT)) vcpu->arch.mdcr_el2 |= MDCR_EL2_TDA; - else - vcpu->arch.mdcr_el2 |= (guest_mdcr & NV_MDCR_GUEST_INCLUDE); } |