Re: [PATCH Part2 v5 43/45] KVM: SVM: Use a VMSA physical address variable for populating VMCB
From: Sean Christopherson <seanjc@google.com>
Date: 2021-10-15 18:58:46
Also in:
kvm, linux-crypto, linux-mm, lkml
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
On Fri, Aug 20, 2021, Brijesh Singh wrote:
From: Tom Lendacky <thomas.lendacky@amd.com> In preparation to support SEV-SNP AP Creation, use a variable that holds the VMSA physical address rather than converting the virtual address. This will allow SEV-SNP AP Creation to set the new physical address that will be used should the vCPU reset path be taken.
The use of "variable" in the changelog and shortlog is really confusing. I read them multiple times and still didn't fully understand the change until I sussed out that the change is to track the PA in vcpu_svm separately from vcpu_svm.vmsa. It's somewhat of a moot point though, because I think this can and should be simplified. In the SEV-ES case, svm->vmcb->control.vmsa_pa is always __pa(svm->vmsa). And in the SNP case, svm->vmcb->control.vmsa_pa defaults to __pa(svm->vmsa), but is not changed on INIT. Rather than do this crazy 3-way dance, simply don't write svm->vmcb->control.vmsa_pa on INIT. Then SNP can change it at will without having an unnecessary and confusing field.
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 1e8b26b93b4f..0bec0b71577e 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c@@ -2593,13 +2593,6 @@ void sev_es_init_vmcb(struct vcpu_svm *svm) svm->vmcb->control.nested_ctl |= SVM_NESTED_CTL_SEV_ES_ENABLE; svm->vmcb->control.virt_ext |= LBR_CTL_ENABLE_MASK; - /* - * An SEV-ES guest requires a VMSA area that is a separate from the - * VMCB page. Do not include the encryption mask on the VMSA physical - * address since hardware will access it using the guest key. - */ - svm->vmcb->control.vmsa_pa = __pa(svm->vmsa); - /* Can't intercept CR register access, HV can't modify CR registers */ svm_clr_intercept(svm, INTERCEPT_CR0_READ); svm_clr_intercept(svm, INTERCEPT_CR4_READ);
@@ -2633,6 +2626,13 @@ void sev_es_init_vmcb(struct vcpu_svm *svm) void sev_es_vcpu_reset(struct vcpu_svm *svm) { + /* + * An SEV-ES guest requires a VMSA area that is a separate from the + * VMCB page. Do not include the encryption mask on the VMSA physical + * address since hardware will access it using the guest key. + */ + svm->vmcb->control.vmsa_pa = __pa(svm->vmsa); + /* * Set the GHCB MSR value as per the GHCB specification when emulating * vCPU RESET for an SEV-ES guest.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
This needs your SoB.