From 57c841f131ef295b583365d2fddd6b0d16e82c10 Mon Sep 17 00:00:00 2001 From: Marc Zyngier Date: Fri, 29 Jan 2016 15:01:28 +0000 Subject: [PATCH] arm/arm64: KVM: Handle out-of-RAM cache maintenance as a NOP So far, our handling of cache maintenance by VA has been pretty simple: Either the access is in the guest RAM and generates a S2 fault, which results in the page being mapped RW, or we go down the io_mem_abort() path, and nuke the guest. The first one is fine, but the second one is extremely weird. Treating the CM as an I/O is wrong, and nothing in the ARM ARM indicates that we should generate a fault for something that cannot end-up in the cache anyway (even if the guest maps it, it will keep on faulting at stage-2 for emulation). So let's just skip this instruction, and let the guest get away with it. Reviewed-by: Christoffer Dall Signed-off-by: Marc Zyngier --- arch/arm/include/asm/kvm_emulate.h | 5 +++++ arch/arm/kvm/mmu.c | 16 ++++++++++++++++ arch/arm64/include/asm/kvm_emulate.h | 5 +++++ 3 files changed, 26 insertions(+) diff --git a/arch/arm/include/asm/kvm_emulate.h b/arch/arm/include/asm/kvm_emulate.h index 8a8c6ded9ca7..ee5328fc4b06 100644 --- a/arch/arm/include/asm/kvm_emulate.h +++ b/arch/arm/include/asm/kvm_emulate.h @@ -138,6 +138,11 @@ static inline bool kvm_vcpu_dabt_iss1tw(struct kvm_vcpu *vcpu) return kvm_vcpu_get_hsr(vcpu) & HSR_DABT_S1PTW; } +static inline bool kvm_vcpu_dabt_is_cm(struct kvm_vcpu *vcpu) +{ + return !!(kvm_vcpu_get_hsr(vcpu) & HSR_DABT_CM); +} + /* Get Access Size from a data abort */ static inline int kvm_vcpu_dabt_get_as(struct kvm_vcpu *vcpu) { diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c index aba61fd3697a..c3eb10ea0971 100644 --- a/arch/arm/kvm/mmu.c +++ b/arch/arm/kvm/mmu.c @@ -1430,6 +1430,22 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run) goto out_unlock; } + /* + * Check for a cache maintenance operation. Since we + * ended-up here, we know it is outside of any memory + * slot. But we can't find out if that is for a device, + * or if the guest is just being stupid. The only thing + * we know for sure is that this range cannot be cached. + * + * So let's assume that the guest is just being + * cautious, and skip the instruction. + */ + if (kvm_vcpu_dabt_is_cm(vcpu)) { + kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu)); + ret = 1; + goto out_unlock; + } + /* * The IPA is reported as [MAX:12], so we need to * complement it with the bottom 12 bits from the diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h index 779a5872a2c5..4df8e7a58c6b 100644 --- a/arch/arm64/include/asm/kvm_emulate.h +++ b/arch/arm64/include/asm/kvm_emulate.h @@ -189,6 +189,11 @@ 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_is_cm(const struct kvm_vcpu *vcpu) +{ + return !!(kvm_vcpu_get_hsr(vcpu) & ESR_ELx_CM); +} + static inline int kvm_vcpu_dabt_get_as(const struct kvm_vcpu *vcpu) { return 1 << ((kvm_vcpu_get_hsr(vcpu) & ESR_ELx_SAS) >> ESR_ELx_SAS_SHIFT);