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    Subject[PATCH 5.2 83/94] KVM: arm/arm64: Only skip MMIO insn once
    Date
    [ Upstream commit 2113c5f62b7423e4a72b890bd479704aa85c81ba ]

    If after an MMIO exit to userspace a VCPU is immediately run with an
    immediate_exit request, such as when a signal is delivered or an MMIO
    emulation completion is needed, then the VCPU completes the MMIO
    emulation and immediately returns to userspace. As the exit_reason
    does not get changed from KVM_EXIT_MMIO in these cases we have to
    be careful not to complete the MMIO emulation again, when the VCPU is
    eventually run again, because the emulation does an instruction skip
    (and doing too many skips would be a waste of guest code :-) We need
    to use additional VCPU state to track if the emulation is complete.
    As luck would have it, we already have 'mmio_needed', which even
    appears to be used in this way by other architectures already.

    Fixes: 0d640732dbeb ("arm64: KVM: Skip MMIO insn after emulation")
    Acked-by: Mark Rutland <mark.rutland@arm.com>
    Signed-off-by: Andrew Jones <drjones@redhat.com>
    Signed-off-by: Marc Zyngier <maz@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    virt/kvm/arm/mmio.c | 7 +++++++
    1 file changed, 7 insertions(+)

    diff --git a/virt/kvm/arm/mmio.c b/virt/kvm/arm/mmio.c
    index a8a6a0c883f1b..6af5c91337f25 100644
    --- a/virt/kvm/arm/mmio.c
    +++ b/virt/kvm/arm/mmio.c
    @@ -86,6 +86,12 @@ int kvm_handle_mmio_return(struct kvm_vcpu *vcpu, struct kvm_run *run)
    unsigned int len;
    int mask;

    + /* Detect an already handled MMIO return */
    + if (unlikely(!vcpu->mmio_needed))
    + return 0;
    +
    + vcpu->mmio_needed = 0;
    +
    if (!run->mmio.is_write) {
    len = run->mmio.len;
    if (len > sizeof(unsigned long))
    @@ -188,6 +194,7 @@ int io_mem_abort(struct kvm_vcpu *vcpu, struct kvm_run *run,
    run->mmio.is_write = is_write;
    run->mmio.phys_addr = fault_ipa;
    run->mmio.len = len;
    + vcpu->mmio_needed = 1;

    if (!ret) {
    /* We handled the access successfully in the kernel. */
    --
    2.20.1


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