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AJvYcCUkVwJKO1FgKJSyojMzYg8vlgIDWFYHKX3EAyMZtzTDQwREKk7cg3iHTvs3/l/VJXOI0ZL/TKG1CBZP@lists.linux.dev X-Gm-Message-State: AOJu0YxTNvKkdNhhtQkrW+sbtdyzn7w+5IQhmS2jhzPzQcEpcQ5uDbiW lAQMNjb0a5hfiZ0az00+rWdQWGKwstbduKhLwYM2t1owDqFrY2jX57fhaSWHUeDB29n1cu72u07 CiQpVmQ== X-Received: from pjsg5.prod.google.com ([2002:a17:90a:7145:b0:352:d19a:6739]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:2242:b0:338:3d07:5174 with SMTP id 98e67ed59e1d1-354870aad4dmr367163a91.5.1770149106374; Tue, 03 Feb 2026 12:05:06 -0800 (PST) Date: Tue, 3 Feb 2026 20:05:05 +0000 In-Reply-To: Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260129011517.3545883-1-seanjc@google.com> <20260129011517.3545883-6-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v5 05/45] KVM: TDX: Drop kvm_x86_ops.link_external_spt(), use .set_external_spte() for all From: Sean Christopherson To: Yan Zhao Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Kiryl Shutsemau , Paolo Bonzini , linux-kernel@vger.kernel.org, linux-coco@lists.linux.dev, kvm@vger.kernel.org, Kai Huang , Rick Edgecombe , Vishal Annapurve , Ackerley Tng , Sagi Shahar , Binbin Wu , Xiaoyao Li , Isaku Yamahata Content-Type: text/plain; charset="us-ascii" On Tue, Feb 03, 2026, Yan Zhao wrote: > On Wed, Jan 28, 2026 at 05:14:37PM -0800, Sean Christopherson wrote: > > static int __must_check set_external_spte_present(struct kvm *kvm, tdp_ptep_t sptep, > > gfn_t gfn, u64 *old_spte, > > u64 new_spte, int level) > > { > > - bool was_present = is_shadow_present_pte(*old_spte); > > - bool is_present = is_shadow_present_pte(new_spte); > > - bool is_leaf = is_present && is_last_spte(new_spte, level); > > - int ret = 0; > > - > > - KVM_BUG_ON(was_present, kvm); > > + int ret; > > > > lockdep_assert_held(&kvm->mmu_lock); > > + > > + if (KVM_BUG_ON(is_shadow_present_pte(*old_spte), kvm)) > > + return -EIO; > Why not move this check of is_shadow_present_pte() to tdx_sept_set_private_spte() > as well? The series gets there eventually, but as of this commit, @old_spte isn't plumbed into tdx_sept_set_private_spte(). > Or also check !is_shadow_present_pte(new_spte) in TDP MMU? Not sure I understand this suggestion. > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c > > index 5688c77616e3..30494f9ceb31 100644 > > --- a/arch/x86/kvm/vmx/tdx.c > > +++ b/arch/x86/kvm/vmx/tdx.c > > @@ -1664,18 +1664,58 @@ static int tdx_mem_page_aug(struct kvm *kvm, gfn_t gfn, > > return 0; > > } > > > > +static struct page *tdx_spte_to_external_spt(struct kvm *kvm, gfn_t gfn, > > + u64 new_spte, enum pg_level level) > > +{ > > + struct kvm_mmu_page *sp = spte_to_child_sp(new_spte); > > + > > + if (KVM_BUG_ON(!sp->external_spt, kvm) || > > + KVM_BUG_ON(sp->role.level + 1 != level, kvm) || > > + KVM_BUG_ON(sp->gfn != gfn, kvm)) > > + return NULL; > Could we remove the KVM_BUG_ON()s, and ... > > > + return virt_to_page(sp->external_spt); > > +} > > + > > +static int tdx_sept_link_private_spt(struct kvm *kvm, gfn_t gfn, > > + enum pg_level level, u64 mirror_spte) > > +{ > > + gpa_t gpa = gfn_to_gpa(gfn); > > + u64 err, entry, level_state; > > + struct page *external_spt; > > + > > + external_spt = tdx_spte_to_external_spt(kvm, gfn, mirror_spte, level); > > + if (!external_spt) > add a KVM_BUG_ON() here? > It could save KVM_BUG_ON()s and have KVM_BUG_ON() match -EIO :) We could, but I don't want to, because if we're going to bother with sanity checks, I want the resulting WARNs to be precise. I.e. I want the WARN to capture *why* tdx_spte_to_external_spt() failed, to make debug/triage easier. > And as Rick also mentioned, better to remove external in external_spt, e.g. > something like pt_page. Yeah, maybe sept_spt? > And mirror_spte --> new_spte? Hmm, ya, I made that change later, but it can probably be shifted here. > > - WARN_ON_ONCE(!is_shadow_present_pte(mirror_spte) || > > - (mirror_spte & VMX_EPT_RWX_MASK) != VMX_EPT_RWX_MASK); > > + WARN_ON_ONCE((mirror_spte & VMX_EPT_RWX_MASK) != VMX_EPT_RWX_MASK); > Also check this for tdx_sept_link_private_spt()? Eh, we could, but I don't think it's necessary. make_nonleaf_spte() is hardcoded to set full permissions (and I don't see that changing any time soon), whereas leaf SPTE protections are much more dynamic.