Re: [PATCH v2 4/7] KVM: x86/mmu: Zap only obsolete roots if a root shadow page is zapped

[Paolo Bonzini]

On 3/2/22 20:45, Sean Christopherson wrote:
> AMD NPT is hosed because KVM's awful ASID scheme doesn't assign an ASID per root
> and doesn't force a new ASID.  IMO, this is an SVM mess and not a TDP MMU bug.

I agree.

> In the short term, I think something like the following would suffice.  Long term,
> we really need to redo SVM ASID management so that ASIDs are tied to a KVM root.


diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c5e3f219803e..7899ca4748c7 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3857,6 +3857,9 @@ static void svm_load_mmu_pgd(struct kvm_vcpu 
*vcpu, hpa_t root_hpa,
        unsigned long cr3;

        if (npt_enabled) {
+               if (is_tdp_mmu_root(root_hpa))
+                       svm->current_vmcb->asid_generation = 0;
+
                svm->vmcb->control.nested_cr3 = __sme_set(root_hpa);
                vmcb_mark_dirty(svm->vmcb, VMCB_NPT);

Why not just new_asid (even unconditionally, who cares)?

BTW yeah, the smoke test worked but the actual one failed horribly.

Paolo