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AHgh+RpzoZUemkgT1xGjF0uenrxjD+2GdpI/Au+MxMAgoizfRFRAj8oFZrAeWTce1KPG14NffukEx9lJZ4tS@lists.linux.dev X-Gm-Message-State: AOJu0Yy4AHaJkFAZHtCN8JBJ4Onzb3vDVBb3p4hFzAY0UWvlfkEGIPIj /tBymRlZZoaV+0XvyntMoz0aXMoV324C5nZ1s6V3rthZacmOc+kNzrVWEZW334jxE+N6aHchMjd 3YTAIxA== X-Received: from pgmh30.prod.google.com ([2002:a63:575e:0:b0:c80:296b:72cc]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:4612:b0:3bf:6c07:b2ed with SMTP id adf61e73a8af0-3c08eebb4d6mr2396075637.48.1783371767923; Mon, 06 Jul 2026 14:02:47 -0700 (PDT) Date: Mon, 6 Jul 2026 14:02:47 -0700 In-Reply-To: <2bdcc07d98df66954b9508be537b6f6a7c9f88de.camel@intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260526023515.288829-1-rick.p.edgecombe@intel.com> <20260526023515.288829-10-rick.p.edgecombe@intel.com> <0c31fcdc-048c-4ff2-9e89-1ba112815c84@linux.intel.com> <2bdcc07d98df66954b9508be537b6f6a7c9f88de.camel@intel.com> Message-ID: Subject: Re: [PATCH v6 09/11] KVM: TDX: Get/put PAMT pages when (un)mapping private memory From: Sean Christopherson To: Rick P Edgecombe Cc: "binbin.wu@linux.intel.com" , "kvm@vger.kernel.org" , "linux-coco@lists.linux.dev" , Kai Huang , Dave Hansen , Yan Y Zhao , "kirill.shutemov@linux.intel.com" , "kas@kernel.org" , "mingo@redhat.com" , "linux-kernel@vger.kernel.org" , "pbonzini@redhat.com" , "nik.borisov@suse.com" , "linux-doc@vger.kernel.org" , "hpa@zytor.com" , "tglx@kernel.org" , Vishal Annapurve , "bp@alien8.de" , Chao Gao , "x86@kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable On Mon, Jul 06, 2026, Rick P Edgecombe wrote: > On Fri, 2026-07-03 at 11:15 +0800, Binbin Wu wrote: > > > @@ -1669,16 +1683,29 @@ static struct page *tdx_spte_to_sept_pt(struc= t kvm > > > *kvm, gfn_t gfn, > > > =C2=A0 static int tdx_sept_map_nonleaf_spte(struct kvm *kvm, gfn_t gf= n, > > > =C2=A0=C2=A0 =C2=A0=C2=A0=C2=A0=C2=A0 enum pg_level level, u64 new= _spte) > > > =C2=A0 { > > > + struct kvm_vcpu *vcpu =3D kvm_get_running_vcpu(); > > > + struct vcpu_tdx *tdx =3D to_tdx(vcpu); > >=20 > > Nit: > > Is it better to move this after checking vcpu is not NULL? > > Although tdx is not dereferenced in between, if vcpu is NULL, > > it means container_of() does arithmetic to a NULL pointer. >=20 > Personally I'm on the fence. I'm going to leave it, because Sean did it t= hat > way: > https://lore.kernel.org/kvm/20260129011517.3545883-23-seanjc@google.com/ Heh, because of course I'm omnipotent and never make mistakes. I agree with the nit in the sense that this isn't a great pattern to encour= age, but IMO the root of the ugly pattern is the use of kvm_get_running_vcpu() (= which is sadly the lesser evil in this case). I.e. I'm not terribly concerned ab= out this code leading to more "problems" in the future. And I don't really wan= t to grab "tdx" later on because that deviates from the standard patterns in KVM= and incorrectly suggests there _is_ a need to pre-check for a non-NULL vCPU. All that said, we can get the bost of both words by simply not caching "tdx= "; there's only one use anyways. diff --git arch/x86/kvm/vmx/tdx.c arch/x86/kvm/vmx/tdx.c index ee073cacafbe..f53bac52449b 100644 --- arch/x86/kvm/vmx/tdx.c +++ arch/x86/kvm/vmx/tdx.c @@ -1684,7 +1684,6 @@ static int tdx_sept_map_nonleaf_spte(struct kvm *kvm,= gfn_t gfn, enum pg_level level, u64 new_spte) { struct kvm_vcpu *vcpu =3D kvm_get_running_vcpu(); - struct vcpu_tdx *tdx =3D to_tdx(vcpu); gpa_t gpa =3D gfn_to_gpa(gfn); u64 err, entry, level_state; struct page *sept_pt; @@ -1697,7 +1696,7 @@ static int tdx_sept_map_nonleaf_spte(struct kvm *kvm,= gfn_t gfn, if (!sept_pt) return -EIO; =20 - ret =3D tdx_pamt_get(page_to_pfn(sept_pt), &tdx->pamt_cache); + ret =3D tdx_pamt_get(page_to_pfn(sept_pt), &to_tdx(vcpu)->pamt_cach= e); if (ret) return ret; =20 @@ -1721,7 +1720,6 @@ static int tdx_sept_map_leaf_spte(struct kvm *kvm, gf= n_t gfn, enum pg_level leve struct kvm_vcpu *vcpu =3D kvm_get_running_vcpu(); struct kvm_tdx *kvm_tdx =3D to_kvm_tdx(kvm); kvm_pfn_t pfn =3D spte_to_pfn(new_spte); - struct vcpu_tdx *tdx =3D to_tdx(vcpu); int ret; =20 if (KVM_BUG_ON(!vcpu, kvm)) @@ -1733,7 +1731,7 @@ static int tdx_sept_map_leaf_spte(struct kvm *kvm, gf= n_t gfn, enum pg_level leve =20 WARN_ON_ONCE((new_spte & VMX_EPT_RWX_MASK) !=3D VMX_EPT_RWX_MASK); =20 - ret =3D tdx_pamt_get(pfn, &tdx->pamt_cache); + ret =3D tdx_pamt_get(pfn, &to_tdx(vcpu)->pamt_cache); if (ret) return ret;