Avi Kivity wrote:
> 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.
Could you elaborate a bit on what the problematic scenario precisely is
(that pending triple faults would not be saved/restored while pending
exceptions are?), and if I/we can do anything to resolve it?
Jan
--
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux
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