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Subject: Re: [PATCH v2] KVM: SVM: Make sure GHCB is mapped before updating
To:     Sean Christopherson <seanjc@google.com>
Cc:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org,
        Paolo Bonzini <pbonzini@redhat.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Brijesh Singh <brijesh.singh@amd.com>
References: <1ed85188bee4a602ffad9632cdf5b5b5c0f40957.1617900892.git.thomas.lendacky@amd.com>
 <YG85HxqEAVd9eEu/@google.com> <923548be-db20-7eea-33aa-571347a95526@amd.com>
 <YG8/WHFOPX6H1eJf@google.com>
From:   Tom Lendacky <thomas.lendacky@amd.com>
Message-ID: <3c28c9bf-d14e-3f9b-0973-ba4a438aaa33@amd.com>
Date:   Thu, 8 Apr 2021 12:47:53 -0500
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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