Re: [PATCH v3 4/5] KVM: nVMX: Fix conditions for interrupt injection

[Jan Kiszka <jan.kiszka@web.de>]

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On 2013-04-11 13:20, Gleb Natapov wrote:
> On Sun, Mar 24, 2013 at 07:44:47PM +0100, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@siemens.com>
>>
>> If we are in guest mode, L0 can only inject events into L2 if L1 has
>> nothing pending. Otherwise, L0 would overwrite L1's events and they
>> would get lost. But even if no injection of L1 is pending, we do not
>> want L0 to interrupt unnecessarily an on going vmentry with all its side
>> effects on the vmcs. Therefore, injection shall be disallowed during
>> L1->L2 transitions. This check is conceptually independent of
>> nested_exit_on_intr.
>>
>> If L1 traps external interrupts, then we also need to look at L1's
>> idt_vectoring_info_field. If it is empty, we can kick the guest from L2
>> to L1, just like the previous code worked.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
>> ---
>>  arch/x86/kvm/vmx.c |   28 ++++++++++++++++++++--------
>>  1 files changed, 20 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index d1bc834..30aa198 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4325,16 +4325,28 @@ static int vmx_nmi_allowed(struct kvm_vcpu *vcpu)
>>  
>>  static int vmx_interrupt_allowed(struct kvm_vcpu *vcpu)
>>  {
>> -	if (is_guest_mode(vcpu) && nested_exit_on_intr(vcpu)) {
>> +	if (is_guest_mode(vcpu)) {
>>  		struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
>> -		if (to_vmx(vcpu)->nested.nested_run_pending ||
>> -		    (vmcs12->idt_vectoring_info_field &
>> -		     VECTORING_INFO_VALID_MASK))
>> +
>> +		if (to_vmx(vcpu)->nested.nested_run_pending)
>>  			return 0;
>> -		nested_vmx_vmexit(vcpu);
>> -		vmcs12->vm_exit_reason = EXIT_REASON_EXTERNAL_INTERRUPT;
>> -		vmcs12->vm_exit_intr_info = 0;
>> -		/* fall through to normal code, but now in L1, not L2 */
>> +		if (nested_exit_on_intr(vcpu)) {
>> +			/*
>> +			 * Check if the idt_vectoring_info_field is free. We
>> +			 * cannot raise EXIT_REASON_EXTERNAL_INTERRUPT if it
>> +			 * isn't.
>> +			 */
>> +			if (vmcs12->idt_vectoring_info_field &
>> +			    VECTORING_INFO_VALID_MASK)
>> +				return 0;
> After patch 2 I do not see how this can be true. Now this case is
> handled by the common code: since event queue is not empty the code will not
> get here.

The event queue is unconditionally cleared (after being migrated to
vmcs12) in patch 2.

Jan



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