Re: [PATCH v2] KVM: SVM: Make sure GHCB is mapped before updating

[Tom Lendacky]

On 4/8/21 12:37 PM, Sean Christopherson wrote:
> On Thu, Apr 08, 2021, Tom Lendacky wrote:
>> On 4/8/21 12:10 PM, Sean Christopherson wrote:
>>> On Thu, Apr 08, 2021, Tom Lendacky wrote:
>>>> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
>>>> index 83e00e524513..7ac67615c070 100644
>>>> --- a/arch/x86/kvm/svm/sev.c
>>>> +++ b/arch/x86/kvm/svm/sev.c
>>>> @@ -2105,5 +2105,8 @@ void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
>>>>  	 * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a
>>>>  	 * non-zero value.
>>>>  	 */
>>>> +	if (WARN_ON_ONCE(!svm->ghcb))
>>>
>>> Isn't this guest triggerable?  I.e. send a SIPI without doing the reset hold?
>>> If so, this should not WARN.
>>
>> Yes, it is a guest triggerable event. But a guest shouldn't be doing that,
>> so I thought adding the WARN_ON_ONCE() just to detect it wasn't bad.
>> Definitely wouldn't want a WARN_ON().
> 
> WARNs are intended only for host issues, e.g. a malicious guest shouldn't be
> able to crash the host when running with panic_on_warn.
> 

Ah, yeah, forgot about panic_on_warn. I can go back to the original patch
or do a pr_warn_once(), any pref?

Thanks,
Tom