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Thu, 30 Oct 2025 16:40:42 -0700 (PDT) Date: Thu, 30 Oct 2025 16:40:40 -0700 In-Reply-To: <6572689b28a76bd95bc653b1fc1131fa57ed7669.camel@intel.com> Mime-Version: 1.0 References: <20251030200951.3402865-1-seanjc@google.com> <20251030200951.3402865-13-seanjc@google.com> <6572689b28a76bd95bc653b1fc1131fa57ed7669.camel@intel.com> Message-ID: Subject: Re: [PATCH v4 12/28] KVM: TDX: WARN if mirror SPTE doesn't have full RWX when creating S-EPT mapping From: Sean Christopherson To: Kai Huang Cc: "chenhuacai@kernel.org" , "frankja@linux.ibm.com" , "maz@kernel.org" , "borntraeger@linux.ibm.com" , "pjw@kernel.org" , "aou@eecs.berkeley.edu" , "kas@kernel.org" , "maobibo@loongson.cn" , "pbonzini@redhat.com" , "maddy@linux.ibm.com" , "palmer@dabbelt.com" , "imbrenda@linux.ibm.com" , "zhaotianrui@loongson.cn" , "anup@brainfault.org" , "oliver.upton@linux.dev" , "kvm@vger.kernel.org" , "linux-coco@lists.linux.dev" , Yan Y Zhao , "michael.roth@amd.com" , "binbin.wu@linux.intel.com" , Ira Weiny , "loongarch@lists.linux.dev" , "ackerleytng@google.com" , "kvmarm@lists.linux.dev" , "linux-kernel@vger.kernel.org" , "kvm-riscv@lists.infradead.org" , Vishal Annapurve , "linuxppc-dev@lists.ozlabs.org" , "linux-arm-kernel@lists.infradead.org" , "linux-mips@vger.kernel.org" , Rick P Edgecombe , "linux-riscv@lists.infradead.org" , "x86@kernel.org" Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20251030_164044_116884_7AB0E33A X-CRM114-Status: GOOD ( 15.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Oct 30, 2025, Kai Huang wrote: > On Thu, 2025-10-30 at 13:09 -0700, Sean Christopherson wrote: > > Pass in the mirror_spte to kvm_x86_ops.set_external_spte() to provide > > symmetry with .remove_external_spte(), and assert in TDX that the mirro= r > > SPTE is shadow-present with full RWX permissions (the TDX-Module doesn'= t > > allow the hypervisor to control protections). > >=20 > > Signed-off-by: Sean Christopherson >=20 > Reviewed-by: Kai Huang >=20 > [...] >=20 > > static int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn, > > - enum pg_level level, kvm_pfn_t pfn) > > + enum pg_level level, u64 mirror_spte) > > { > > struct kvm_tdx *kvm_tdx =3D to_kvm_tdx(kvm); > > + kvm_pfn_t pfn =3D spte_to_pfn(mirror_spte); > > =20 > > /* TODO: handle large pages. */ > > if (KVM_BUG_ON(level !=3D PG_LEVEL_4K, kvm)) > > return -EIO; > > =20 > > + WARN_ON_ONCE(!is_shadow_present_pte(mirror_spte) || > > + (mirror_spte & VMX_EPT_RWX_MASK) !=3D VMX_EPT_RWX_MASK); > > + >=20 > Nit:=C2=A0 >=20 > I am a little bit confused about when to use WARN_ON_ONCE() and > KVM_BUG_ON(). :-) Very loosely: WARN if there's a decent chance carrying on might be fine, KVM_BUG_ON() if there's a good chance carrying on will crash the host and/o= r corrupt the guest, e.g. if KVM suspects a hardware/TDX-Module issue.