Hello, On Tue, Dec 20, 2022 at 08:09:22PM +0000, Marc Zyngier wrote: > As a minor optimisation, we can retrofit the "S1PTW is a write > even on translation fault" concept *if* the vcpu is using the > HW-managed Access Flag, as setting TCR_EL1.HA is guaranteed > to result in an update of the PTE. > > However, we cannot do the same thing for DB, as it would require > us to parse the PTs to find out if the DBM bit is set there. > This is not going to happen. > > Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> > --- > arch/arm64/include/asm/kvm_emulate.h | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > index fd6ad8b21f85..4ee467065042 100644 > --- a/arch/arm64/include/asm/kvm_emulate.h > +++ b/arch/arm64/include/asm/kvm_emulate.h > @@ -374,6 +374,9 @@ static __always_inline int kvm_vcpu_sys_get_rt(struct kvm_vcpu *vcpu) > static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu) > { > if (kvm_vcpu_abt_iss1tw(vcpu)) { > + unsigned int afdb; > + u64 mmfr1; > + > /* > * Only a permission fault on a S1PTW should be > * considered as a write. Otherwise, page tables baked > @@ -385,12 +388,27 @@ static inline bool kvm_is_write_fault(struct kvm_vcpu *vcpu) > * to map the page containing the PT (read only at > * first), then a permission fault to allow the flags > * to be set. > + * > + * We can improve things if the guest uses AF, as this > + * is guaranteed to result in a write to the PTE. For > + * DB, however, we'd need to parse the guest's PTs, > + * and that's not on. DB is crap anyway. > */ > switch (kvm_vcpu_trap_get_fault_type(vcpu)) { Nit: fault_status is calculated once when taking the fault, and passed around to all users (like user_mem_abort()). Not sure if this is because of the extra cycles needed to get it, or just style. Anyway, maybe it applies here. > case ESR_ELx_FSC_PERM: > return true; > default: > - return false; > + /* Can't introspect TCR_EL1 with pKVM */ > + if (kvm_vm_is_protected(vcpu->kvm)) > + return false; > + > + mmfr1 = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1); > + afdb = cpuid_feature_extract_unsigned_field(mmfr1, ID_AA64MMFR1_EL1_HAFDBS_SHIFT); > + > + if (afdb == ID_AA64MMFR1_EL1_HAFDBS_NI) > + return false; > + > + return (vcpu_read_sys_reg(vcpu, TCR_EL1) & TCR_HA); Also tested this specific case using page_fault_test when the PT page is marked for dirty logging with and without AF. In both cases there's a single _FSC_FAULT (no PERM_FAUT) as expected, and the PT page is marked dirty in the AF case. The RO and UFFD cases also work as expected. Need to send some changes for page_fault_test as many tests assume that any S1PTW is always a PT write, and are failing. Also need to add some new tests for PTs in RO memslots (as it didn't make much sense before this change). > } > } > > -- > 2.34.1 > > _______________________________________________ > kvmarm mailing list > kvmarm@xxxxxxxxxxxxxxxxxxxxx > https://lists.cs.columbia.edu/mailman/listinfo/kvmarm Reviewed-by: Ricardo Koller <ricarkol@xxxxxxxxxx> Thanks, Ricardo