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AHgh+RqvLjaPHeQW2i3ivq0PBfN/QgsMG/5KAg5TO+kWSqFaD6UTnZsAH/8aigeBMF+UhlSKLy8=@vger.kernel.org X-Gm-Message-State: AOJu0Yy8DlObh0A58trv0WbWCroQX07kVQxE3vgF9yQ7mdY575fVJIRq boMf6QbnLHCOAs8ghQMJiGtG4whhNYk1sZmK1R442XFg+Dg9PPrq9K24p+KgcoKpQLkfmXLZ+HS icBIKEg== X-Received: from pfbgh5.prod.google.com ([2002:a05:6a00:6385:b0:845:48ff:3362]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:987:b0:847:8b1d:230d with SMTP id d2e1a72fcca58-84f69421bcamr3113008b3a.3.1786141107295; Fri, 07 Aug 2026 15:18:27 -0700 (PDT) Date: Fri, 7 Aug 2026 15:18:26 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260806214050.78058-1-seanjc@google.com> <20260806214050.78058-3-seanjc@google.com> Message-ID: Subject: Re: [PATCH 2/4] KVM: x86/mmu: Harden "map private PFN" against unexpected root invalidation From: Sean Christopherson To: Rick P Edgecombe Cc: "pbonzini@redhat.com" , "sashiko-bot@kernel.org" , "kvm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Kai Huang , Yan Y Zhao Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Fri, Aug 07, 2026, Rick P Edgecombe wrote: > On Thu, 2026-08-06 at 14:40 -0700, Sean Christopherson wrote: > > @@ -5199,10 +5195,21 @@ int kvm_tdp_mmu_map_private_pfn(struct kvm_vcpu= *vcpu, gfn_t gfn, kvm_pfn_t pfn) > > =C2=A0 if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu)) > > =C2=A0 return -EIO; > > =C2=A0 > > + r =3D kvm_mmu_reload(vcpu); > > + if (r) > > + return r; > > + > > =C2=A0 cond_resched(); > > =C2=A0 > > =C2=A0 guard(read_lock)(&kvm->mmu_lock); > > =C2=A0 > > + /* > > + * Because slots_lock is held, it should be impossible for roots > > + * to be invalidated after the initial MMU reload.=C2=A0 WARN, but > > + * continue and re-reload the MMU to try and keep the VM alive. > > + */ >=20 > It might be a little confusing when no MMU reload follows the comment. Ma= ybe > mention that the MMU reload is above? Either way ok to me. Yeah, I don't love the comment either. The subtlety that it doesn't captur= e is that KVM_REQ_MMU_FREE_OBSOLETE_ROOTS doesn't actually mean the current root= is invalid, just that it might be invalid and the vCPU needs to check. How about this? =20 /* * Because slots_lock is held, it should be impossible for *any* * roots to be invalidated after the initial MMU reload. WARN, * but continue on; the above MMU reload will do the right thing * if the current root is actually invalid. */ > > + WARN_ON_ONCE(kvm_test_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu)= ); > > + > > =C2=A0 r =3D kvm_tdp_mmu_map(vcpu, &fault); >=20