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Message-ID: <7f55f8cb-caac-ab81-82f2-f0d29e4a0c6a@oracle.com>
Date: Thu, 20 Jan 2022 16:46:35 +0000
From: Liam Merwick <liam.merwick@...cle.com>
To: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org,
Tom Lendacky <thomas.lendacky@....com>,
Brijesh Singh <brijesh.singh@....com>,
Liam Merwick <liam.merwick@...cle.com>
Subject: Re: [PATCH 9/9] KVM: SVM: Don't kill SEV guest if SMAP erratum
triggers in usermode
On 20/01/2022 01:07, Sean Christopherson wrote:
> Inject a #GP instead of synthesizing triple fault to try to avoid killing
> the guest if emulation of an SEV guest fails due to encountering the SMAP
> erratum. The injected #GP may still be fatal to the guest, e.g. if the
> userspace process is providing critical functionality, but KVM should
> make every attempt to keep the guest alive.
>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Liam Merwick <liam.merwick@...cle.com>
> ---
> arch/x86/kvm/svm/svm.c | 16 +++++++++++++++-
> 1 file changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index a4b02a6217fd..88f5bbb0e6a1 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4357,7 +4357,21 @@ static bool svm_can_emulate_instruction(struct kvm_vcpu *vcpu, int emul_type,
> is_user = svm_get_cpl(vcpu) == 3;
> if (smap && (!smep || is_user)) {
> pr_err_ratelimited("KVM: SEV Guest triggered AMD Erratum 1096\n");
> - kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> +
> + /*
> + * If the fault occurred in userspace, arbitrarily inject #GP
> + * to avoid killing the guest and to hopefully avoid confusing
> + * the guest kernel too much, e.g. injecting #PF would not be
> + * coherent with respect to the guest's page tables. Request
> + * triple fault if the fault occurred in the kernel as there's
> + * no fault that KVM can inject without confusing the guest.
> + * In practice, the triple fault is moot as no sane SEV kernel
> + * will execute from user memory while also running with SMAP=1.
> + */
> + if (is_user)
> + kvm_inject_gp(vcpu, 0);
> + else
> + kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> }
>
> resume_guest:
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