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KVM: SEV: Ignore MMIO requests of length '0'

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Explicitly ignore MMIO requests of length '0', so that setting up the
software scratch area (and other code) doesn't have to worry about
underflowing the length, and to allow for special casing '0' in the
future.

Fixes: 8f423a80d2 ("KVM: SVM: Support MMIO for an SEV-ES guest")
Cc: stable@vger.kernel.org
Reviewed-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20260501202250.2115252-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2026-05-01 13:22:27 -07:00 committed by Paolo Bonzini
parent db3f2195d2
commit 1aa8a6dc7d
1 changed files with 7 additions and 3 deletions
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10
arch/x86/kvm/svm/sev.c
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@ -4497,13 +4497,17 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
case SVM_VMGEXIT_MMIO_READ:
case SVM_VMGEXIT_MMIO_WRITE: {
bool is_write = control->exit_code == SVM_VMGEXIT_MMIO_WRITE;
u64 len = control->exit_info_2;
ret = setup_vmgexit_scratch(svm, !is_write, control->exit_info_2);
if (!len)
return 1;
ret = setup_vmgexit_scratch(svm, !is_write, len);
if (ret)
break;
ret = kvm_sev_es_mmio(vcpu, is_write, control->exit_info_1,
control->exit_info_2, svm->sev_es.ghcb_sa);
ret = kvm_sev_es_mmio(vcpu, is_write, control->exit_info_1, len,
svm->sev_es.ghcb_sa);
break;
}
case SVM_VMGEXIT_NMI_COMPLETE: