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AJvYcCWse6rabLQnoZ0rMlj97qpD6/yIbEQ0635WxMr4ryd1nRb0vJN7I8e2H8WmK1QzVwHQisHUqFyLPAH5q4LkCR7WO/Q= X-Gm-Message-State: AOJu0Yz2SyuWwdmVA4TdT7xzHnpSy2USHYj4wuNahPatf7pfl6+soYiC 3sfaATUTVF/cFrR+jU/3OhkUN5c+Yglh6kbrScg0GQj+32pBL2K0Ji8600m1X0agAzKohGvjXNm ZYU8X21asm7GetRqLKVDfEaRqUdtQWtX/gmbQFQubN8vlty22BMhZ28N7uUDKfce9RlRYvnfrQ+ ry1ygy8zcE8CbvVS/EhB7gMPo= X-Received: by 2002:a5d:5351:0:b0:343:e02f:1a46 with SMTP id ffacd0b85a97d-3504a62fb12mr2102084f8f.2.1715349038940; Fri, 10 May 2024 06:50:38 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHucRBfWSHvPvamu1WRWuBFTrQrQkQyBe+ROxdfO0QRjONS8tJPWThU8+2GOiv3nf4H2QrNLg23m2TZKw0gXJM= X-Received: by 2002:a5d:5351:0:b0:343:e02f:1a46 with SMTP id ffacd0b85a97d-3504a62fb12mr2102054f8f.2.1715349038422; Fri, 10 May 2024 06:50:38 -0700 (PDT) MIME-Version: 1.0 References: <20240501085210.2213060-1-michael.roth@amd.com> <20240510015822.503071-1-michael.roth@amd.com> In-Reply-To: From: Paolo Bonzini Date: Fri, 10 May 2024 15:50:26 +0200 Message-ID: Subject: Re: [PATCH v15 21/23] KVM: MMU: Disable fast path for private memslots To: Sean Christopherson Cc: Michael Roth , kvm@vger.kernel.org, linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com, papaluri@amd.com, Isaku Yamahata X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 1E61F1C0023 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: gr631yyqixjd5p3s9zbzpt9f73enapg7 X-HE-Tag: 1715349041-382047 X-HE-Meta: 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 KU4rHapz giyvCasLs1t4Cmq7zzPnCeLCMjc+VzaYOLDihumopirBQfw9A2doYr778bPWLXvhN8GpodJ9ltp4ZXvaWCjTZxPTrSs0uiu58VWieG30hTq33OWV6YHE7/M/FvWFPFxFNHDGXuWNB3WGyczQPEuV5bLQQUNUVy99zReDMquLOuNsIZ2uIHEnz2B1MciKFFP1x0odi7XfPoN/aDYxAQ67y0+lo2T0fBM5tNptwMuBG3y0E7d7nC3atb5mLN6vpSjt+Bft/54hmbMHjetX+4CCuVeaNmVQTg3dZ1QGbUboP7UEB8lvGAgFCR43cog== X-Bogosity: Ham, tests=bogofilter, spamicity=0.010765, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 10, 2024 at 3:47=E2=80=AFPM Sean Christopherson wrote: > > > + * Since software-protected VMs don't have a notion of a shared v= s. > > + * private that's separate from what KVM is tracking, the above > > + * KVM_EXIT_MEMORY_FAULT condition wouldn't occur, so avoid the > > + * special handling for that case for now. > > Very technically, it can occur if userspace _just_ modified the attribute= s. And > as I've said multiple times, at least for now, I want to avoid special ca= sing > SW-protected VMs unless it is *absolutely* necessary, because their sole = purpose > is to allow testing flows that are impossible to excercise without SNP/TD= X hardware. Yep, it is not like they have to be optimized. > > + */ > > + if (kvm_slot_can_be_private(fault->slot) && > > + !(IS_ENABLED(CONFIG_KVM_SW_PROTECTED_VM) && > > + vcpu->kvm->arch.vm_type =3D=3D KVM_X86_SW_PROTECTED_VM)) > > Heh, !(x && y) kills me, I misread this like 4 times. > > Anyways, I don't like the heuristic. It doesn't tie the restriction back= to the > cause in any reasonable way. Can't this simply be? > > if (fault->is_private !=3D kvm_mem_is_private(vcpu->kvm, fault->g= fn) > return false; You beat me to it by seconds. And it can also be guarded by a check on kvm->arch.has_private_mem to avoid the attributes lookup. > Which is much, much more self-explanatory. Both more self-explanatory and more correct. Paolo