Jan Kiszka wrote:
> Joerg Roedel wrote:
>
>> The current KVM x86 exception code handles double and triple faults only for
>> page fault exceptions. This patch extends this detection for every exception
>> that gets queued for the guest.
>>
>> Signed-off-by: Joerg Roedel <[EMAIL PROTECTED]>
>> Cc: Jan Kiszka <[EMAIL PROTECTED]>
>> ---
>> arch/x86/kvm/x86.c | 31 +++++++++++++++++--------------
>> 1 files changed, 17 insertions(+), 14 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 578a0c1..c05aa32 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -144,9 +144,21 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
>> }
>> EXPORT_SYMBOL_GPL(kvm_set_apic_base);
>>
>> +static void handle_multiple_faults(struct kvm_vcpu *vcpu)
>> +{
>> + if (vcpu->arch.exception.nr != DF_VECTOR) {
>> + vcpu->arch.exception.nr = DF_VECTOR;
>> + vcpu->arch.exception.error_code = 0;
>> + } else
>> + set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
>> +}
>> +
>> void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
>> {
>> - WARN_ON(vcpu->arch.exception.pending);
>> + if (vcpu->arch.exception.pending) {
>> + handle_multiple_faults(vcpu);
>> + return;
>> + }
>> vcpu->arch.exception.pending = true;
>> vcpu->arch.exception.has_error_code = false;
>> vcpu->arch.exception.nr = nr;
>> @@ -157,25 +169,16 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu,
>> unsigned long addr,
>> u32 error_code)
>> {
>> ++vcpu->stat.pf_guest;
>> - if (vcpu->arch.exception.pending) {
>> - 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;
>> kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
>> }
>>
>> void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32
>> error_code)
>> {
>> - WARN_ON(vcpu->arch.exception.pending);
>> + if (vcpu->arch.exception.pending) {
>> + handle_multiple_faults(vcpu);
>> + return;
>> + }
>> vcpu->arch.exception.pending = true;
>> vcpu->arch.exception.has_error_code = true;
>> vcpu->arch.exception.nr = nr;
>>
>
> And here is an add-on patch to fix reset-on-triple-fault:
>
>
> Clear the pending original exception when raising a triple fault. This
> allows to re-use the vcpu instance, e.g. after a reset which is
> typically issued as reaction on the triple fault.
>
> Signed-off-by: Jan Kiszka <[EMAIL PROTECTED]>
>
> ---
> arch/x86/kvm/x86.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> Index: b/arch/x86/kvm/x86.c
> ===================================================================
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -149,8 +149,10 @@ static void handle_multiple_faults(struc
> if (vcpu->arch.exception.nr != DF_VECTOR) {
> vcpu->arch.exception.nr = DF_VECTOR;
> vcpu->arch.exception.error_code = 0;
> - } else
> + } else {
> set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
> + vcpu->arch.exception.pending = false;
> + }
> }
>
> void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
>
>
There's a bigger problem here. The exception queue is hidden state that
qemu and load and save.
--
Any sufficiently difficult bug is indistinguishable from a feature.
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