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    Subject[PATCH 11/35] KVM: detect if VCPU triple faults
    Date
    From: Joerg Roedel <joerg.roedel@amd.com>

    In the current inject_page_fault path KVM only checks if there is another PF
    pending and injects a DF then. But it has to check for a pending DF too to
    detect a shutdown condition in the VCPU. If this is not detected the VCPU goes
    to a PF -> DF -> PF loop when it should triple fault. This patch detects this
    condition and handles it with an KVM_SHUTDOWN exit to userspace.

    Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
    Signed-off-by: Avi Kivity <avi@qumranet.com>
    ---
    arch/x86/kvm/x86.c | 20 +++++++++++++++-----
    include/linux/kvm_host.h | 1 +
    2 files changed, 16 insertions(+), 5 deletions(-)

    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index dbcff38..491eda3 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -155,11 +155,16 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
    u32 error_code)
    {
    ++vcpu->stat.pf_guest;
    - if (vcpu->arch.exception.pending && vcpu->arch.exception.nr == PF_VECTOR) {
    - printk(KERN_DEBUG "kvm: inject_page_fault:"
    - " double fault 0x%lx\n", addr);
    - vcpu->arch.exception.nr = DF_VECTOR;
    - vcpu->arch.exception.error_code = 0;
    + if (vcpu->arch.exception.pending) {
    + if (vcpu->arch.exception.nr == PF_VECTOR) {
    + printk(KERN_DEBUG "kvm: inject_page_fault:"
    + " double fault 0x%lx\n", addr);
    + vcpu->arch.exception.nr = DF_VECTOR;
    + vcpu->arch.exception.error_code = 0;
    + } else if (vcpu->arch.exception.nr == DF_VECTOR) {
    + /* triple fault -> shutdown */
    + set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
    + }
    return;
    }
    vcpu->arch.cr2 = addr;
    @@ -2676,6 +2681,11 @@ again:
    r = 0;
    goto out;
    }
    + if (test_and_clear_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests)) {
    + kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
    + r = 0;
    + goto out;
    + }
    }

    kvm_inject_pending_timer_irqs(vcpu);
    diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
    index 9750bb3..958e003 100644
    --- a/include/linux/kvm_host.h
    +++ b/include/linux/kvm_host.h
    @@ -38,6 +38,7 @@
    #define KVM_REQ_MIGRATE_TIMER 1
    #define KVM_REQ_REPORT_TPR_ACCESS 2
    #define KVM_REQ_MMU_RELOAD 3
    +#define KVM_REQ_TRIPLE_FAULT 4

    struct kvm_vcpu;
    extern struct kmem_cache *kvm_vcpu_cache;
    --
    1.5.4.5


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