Re: [PATCH Part2 RFC v4 26/40] KVM: SVM: Add KVM_SEV_SNP_LAUNCH_FINISH command

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On Mon, Jul 19, 2021, Brijesh Singh wrote:
> 
> 
> On 7/19/21 11:54 AM, Sean Christopherson wrote:
> > > As I said in previous comments that by default all the memory is in the
> > > hypervisor state. if the rmpupdate() failed that means nothing is changed in
> > > the RMP and there is no need to reclaim. The reclaim is required only if the
> > > pages are assigned in the RMP table.
> > 
> > I wasn't referring to RMPUPDATE failing here (or anywhere).  This is the vCPU free
> > path, which I think means the svm->vmsa page was successfully updated in the RMP
> > during LAUNCH_UPDATE.  snp_launch_update_vmsa() goes through snp_page_reclaim()
> > on LAUNCH_UPDATE failure, whereas this happy path does not.  Is there some other
> > transition during teardown that obviastes the need for reclaim?  If so, a comment
> > to explain that would be very helpful.
> > 
> 
> In this patch, the sev_free_vcpu() hunk takes care of reclaiming the vmsa
> pages before releasing it. I think it will make it more obvious after I add
> a helper so that we don't depend on user reading the comment block to see
> what its doing.

Where?  I feel like I'm missing something.  The only change to sev_free_vcpu() I
see is that addition of the rmpupdate(), I don't see any reclaim path.

@@ -2346,8 +2454,25 @@ void sev_free_vcpu(struct kvm_vcpu *vcpu)

        if (vcpu->arch.guest_state_protected)
                sev_flush_guest_memory(svm, svm->vmsa, PAGE_SIZE);
+
+       /*
+        * If its an SNP guest, then VMSA was added in the RMP entry as a guest owned page.
+        * Transition the page to hyperivosr state before releasing it back to the system.
+        */
+       if (sev_snp_guest(vcpu->kvm)) {
+               struct rmpupdate e = {};
+               int rc;
+
+               rc = rmpupdate(virt_to_page(svm->vmsa), &e);
+               if (rc) {
+                       pr_err("Failed to release SNP guest VMSA page (rc %d), leaking it\n", rc);
+                       goto skip_vmsa_free;
+               }
+       }
+
        __free_page(virt_to_page(svm->vmsa));

+skip_vmsa_free:
        if (svm->ghcb_sa_free)
                kfree(svm->ghcb_sa);
 }



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