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Date:   Wed, 2 Mar 2022 21:39:04 +0100
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Subject: Re: [PATCH v2 4/7] KVM: x86/mmu: Zap only obsolete roots if a root
 shadow page is zapped
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To:     Sean Christopherson <seanjc@google.com>
Cc:     Christian Borntraeger <borntraeger@linux.ibm.com>,
        Janosch Frank <frankja@linux.ibm.com>,
        David Hildenbrand <david@redhat.com>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Ben Gardon <bgardon@google.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>
References: <20220225182248.3812651-1-seanjc@google.com>
 <20220225182248.3812651-5-seanjc@google.com>
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 <ee757515-4a0f-c5cb-cd57-04983f62f499@redhat.com>
 <Yh/JdHphCLOm4evG@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <Yh/JdHphCLOm4evG@google.com>
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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