From: Will Deacon <will@kernel.org> To: kvmarm@lists.cs.columbia.edu Cc: kernel-team@android.com, Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/7] KVM: arm64: Update comment when skipping guest MMIO access instruction Date: Fri, 24 Jul 2020 15:35:00 +0100 [thread overview] Message-ID: <20200724143506.17772-2-will@kernel.org> (raw) In-Reply-To: <20200724143506.17772-1-will@kernel.org> If a 32-bit guest accesses MMIO using a 16-bit Thumb-2 instruction that is reported to the hypervisor without a valid syndrom (for example, because of the addressing mode), then we may hand off the fault to userspace. When resuming the guest, we unconditionally advance the PC by 4 bytes, since ESR_EL2.IL is always 1 for data aborts generated without a valid syndrome. This is a bit rubbish, but it's also difficult to see how we can fix it without potentially introducing regressions in userspace MMIO fault handling. Update the comment when skipping a guest MMIO access instruction so that this corner case is at least written down. Cc: Marc Zyngier <maz@kernel.org> Cc: Quentin Perret <qperret@google.com> Signed-off-by: Will Deacon <will@kernel.org> --- arch/arm64/kvm/mmio.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c index 4e0366759726..b54ea5aa6c06 100644 --- a/arch/arm64/kvm/mmio.c +++ b/arch/arm64/kvm/mmio.c @@ -113,6 +113,13 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run) /* * The MMIO instruction is emulated and should not be re-executed * in the guest. + * + * Note: If user space handled the emulation because the abort + * symdrome information was not valid (ISV set in the ESR), then + * this will assume that the faulting instruction was 32-bit. + * If the faulting instruction was a 16-bit Thumb instruction, + * then userspace would need to rewind the PC by 2 bytes prior to + * resuming the vCPU (yuck!). */ kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu)); -- 2.28.0.rc0.142.g3c755180ce-goog _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
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From: Will Deacon <will@kernel.org> To: kvmarm@lists.cs.columbia.edu Cc: Quentin Perret <qperret@google.com>, kernel-team@android.com, Suzuki Poulose <suzuki.poulose@arm.com>, James Morse <james.morse@arm.com>, Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>, linux-arm-kernel@lists.infradead.org Subject: [PATCH 1/7] KVM: arm64: Update comment when skipping guest MMIO access instruction Date: Fri, 24 Jul 2020 15:35:00 +0100 [thread overview] Message-ID: <20200724143506.17772-2-will@kernel.org> (raw) In-Reply-To: <20200724143506.17772-1-will@kernel.org> If a 32-bit guest accesses MMIO using a 16-bit Thumb-2 instruction that is reported to the hypervisor without a valid syndrom (for example, because of the addressing mode), then we may hand off the fault to userspace. When resuming the guest, we unconditionally advance the PC by 4 bytes, since ESR_EL2.IL is always 1 for data aborts generated without a valid syndrome. This is a bit rubbish, but it's also difficult to see how we can fix it without potentially introducing regressions in userspace MMIO fault handling. Update the comment when skipping a guest MMIO access instruction so that this corner case is at least written down. Cc: Marc Zyngier <maz@kernel.org> Cc: Quentin Perret <qperret@google.com> Signed-off-by: Will Deacon <will@kernel.org> --- arch/arm64/kvm/mmio.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/arm64/kvm/mmio.c b/arch/arm64/kvm/mmio.c index 4e0366759726..b54ea5aa6c06 100644 --- a/arch/arm64/kvm/mmio.c +++ b/arch/arm64/kvm/mmio.c @@ -113,6 +113,13 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run) /* * The MMIO instruction is emulated and should not be re-executed * in the guest. + * + * Note: If user space handled the emulation because the abort + * symdrome information was not valid (ISV set in the ESR), then + * this will assume that the faulting instruction was 32-bit. + * If the faulting instruction was a 16-bit Thumb instruction, + * then userspace would need to rewind the PC by 2 bytes prior to + * resuming the vCPU (yuck!). */ kvm_skip_instr(vcpu, kvm_vcpu_trap_il_is32bit(vcpu)); -- 2.28.0.rc0.142.g3c755180ce-goog _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2020-07-24 14:35 UTC|newest] Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-07-24 14:34 [PATCH 0/7] KVM: arm64: Fixes to early stage-2 fault handling Will Deacon 2020-07-24 14:34 ` Will Deacon 2020-07-24 14:35 ` Will Deacon [this message] 2020-07-24 14:35 ` [PATCH 1/7] KVM: arm64: Update comment when skipping guest MMIO access instruction Will Deacon 2020-07-26 11:08 ` Marc Zyngier 2020-07-26 11:08 ` Marc Zyngier 2020-07-27 10:30 ` Will Deacon 2020-07-27 10:30 ` Will Deacon 2020-07-24 14:35 ` [PATCH 2/7] KVM: arm64: Rename kvm_vcpu_dabt_isextabt() Will Deacon 2020-07-24 14:35 ` Will Deacon 2020-07-26 11:15 ` Marc Zyngier 2020-07-26 11:15 ` Marc Zyngier 2020-07-27 10:30 ` Will Deacon 2020-07-27 10:30 ` Will Deacon 2020-07-24 14:35 ` [PATCH 3/7] KVM: arm64: Handle data and instruction external aborts the same way Will Deacon 2020-07-24 14:35 ` Will Deacon 2020-07-24 14:35 ` [PATCH 4/7] KVM: arm64: Remove useless local variable Will Deacon 2020-07-24 14:35 ` Will Deacon 2020-07-24 14:35 ` [PATCH 5/7] KVM: arm64: Move 'invalid syndrome' logic out of io_mem_abort() Will Deacon 2020-07-24 14:35 ` Will Deacon 2020-07-26 11:55 ` Marc Zyngier 2020-07-26 11:55 ` Marc Zyngier 2020-07-27 10:31 ` Will Deacon 2020-07-27 10:31 ` Will Deacon 2020-07-24 14:35 ` [PATCH 6/7] KVM: arm64: Handle stage-2 faults on stage-1 page-table walks earlier Will Deacon 2020-07-24 14:35 ` Will Deacon 2020-07-26 13:38 ` Marc Zyngier 2020-07-26 13:38 ` Marc Zyngier 2020-07-27 10:29 ` Will Deacon 2020-07-27 10:29 ` Will Deacon 2020-07-24 14:35 ` [PATCH 7/7] KVM: arm64: Separate write faults on read-only memslots from MMIO Will Deacon 2020-07-24 14:35 ` Will Deacon
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