diff options
authorWill Deacon <will.deacon@arm.com>2016-09-29 12:37:01 +0100
committerMarc Zyngier <marc.zyngier@arm.com>2016-10-21 17:25:47 +0100
commit60e21a0ef54cd836b9eb22c7cb396989b5b11648 (patch)
parent1001354ca34179f3db924eb66672442a173147dc (diff)
arm64: KVM: Take S1 walks into account when determining S2 write faults
The WnR bit in the HSR/ESR_EL2 indicates whether a data abort was generated by a read or a write instruction. For stage 2 data aborts generated by a stage 1 translation table walk (i.e. the actual page table access faults at EL2), the WnR bit therefore reports whether the instruction generating the walk was a load or a store, *not* whether the page table walker was reading or writing the entry. For page tables marked as read-only at stage 2 (e.g. due to KSM merging them with the tables from another guest), this could result in livelock, where a page table walk generated by a load instruction attempts to set the access flag in the stage 1 descriptor, but fails to trigger CoW in the host since only a read fault is reported. This patch modifies the arm64 kvm_vcpu_dabt_iswrite function to take into account stage 2 faults in stage 1 walks. Since DBM cannot be disabled at EL2 for CPUs that implement it, we assume that these faults are always causes by writes, avoiding the livelock situation at the expense of occasional, spurious CoWs. We could, in theory, do a bit better by checking the guest TCR configuration and inspecting the page table to see why the PTE faulted. However, I doubt this is measurable in practice, and the threat of livelock is real. Cc: <stable@vger.kernel.org> Cc: Julien Grall <julien.grall@arm.com> Reviewed-by: Marc Zyngier <marc.zyngier@arm.com> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org> Signed-off-by: Will Deacon <will.deacon@arm.com>
1 files changed, 6 insertions, 5 deletions
diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
index fd9d5fd788f5..f5ea0ba70f07 100644
--- a/arch/arm64/include/asm/kvm_emulate.h
+++ b/arch/arm64/include/asm/kvm_emulate.h
@@ -178,11 +178,6 @@ static inline bool kvm_vcpu_dabt_isvalid(const struct kvm_vcpu *vcpu)
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_ISV);
-static inline bool kvm_vcpu_dabt_iswrite(const struct kvm_vcpu *vcpu)
- return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WNR);
static inline bool kvm_vcpu_dabt_issext(const struct kvm_vcpu *vcpu)
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SSE);
@@ -203,6 +198,12 @@ static inline bool kvm_vcpu_dabt_iss1tw(const struct kvm_vcpu *vcpu)
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_S1PTW);
+static inline bool kvm_vcpu_dabt_iswrite(const struct kvm_vcpu *vcpu)
+ return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_WNR) ||
+ kvm_vcpu_dabt_iss1tw(vcpu); /* AF/DBM update */
static inline bool kvm_vcpu_dabt_is_cm(const struct kvm_vcpu *vcpu)
return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM);