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Wed, 25 Jun 2025 06:33:31 +0000 Received: from EX19D015EUB004.ant.amazon.com ([fe80::2dc9:7aa9:9cd3:fc8a]) by EX19D015EUB004.ant.amazon.com ([fe80::2dc9:7aa9:9cd3:fc8a%3]) with mapi id 15.02.1544.014; Wed, 25 Jun 2025 06:33:31 +0000 From: "Roy, Patrick" To: "ackerleytng@google.com" , Sean Christopherson , Fuad Tabba CC: "akpm@linux-foundation.org" , "amoorthy@google.com" , "anup@brainfault.org" , "aou@eecs.berkeley.edu" , "brauner@kernel.org" , "catalin.marinas@arm.com" , "chao.p.peng@linux.intel.com" , "chenhuacai@kernel.org" , "david@redhat.com" , "dmatlack@google.com" , "fvdl@google.com" , "hch@infradead.org" , "hughd@google.com" , "ira.weiny@intel.com" , "isaku.yamahata@gmail.com" , "isaku.yamahata@intel.com" , "james.morse@arm.com" , "jarkko@kernel.org" , "jgg@nvidia.com" , "jhubbard@nvidia.com" , "jthoughton@google.com" , "keirf@google.com" , "kirill.shutemov@linux.intel.com" , "kvm@vger.kernel.org" , "kvmarm@lists.linux.dev" , "liam.merwick@oracle.com" , "linux-arm-msm@vger.kernel.org" , "linux-mm@kvack.org" , "mail@maciej.szmigiero.name" , "maz@kernel.org" , "mic@digikod.net" , "michael.roth@amd.com" , "mpe@ellerman.id.au" , "oliver.upton@linux.dev" , "palmer@dabbelt.com" , "pankaj.gupta@amd.com" , "paul.walmsley@sifive.com" , "pbonzini@redhat.com" , "peterx@redhat.com" , "qperret@google.com" , "quic_cvanscha@quicinc.com" , "quic_eberman@quicinc.com" , "quic_mnalajal@quicinc.com" , "quic_pderrin@quicinc.com" , "quic_pheragu@quicinc.com" , "quic_svaddagi@quicinc.com" , "quic_tsoni@quicinc.com" , "rientjes@google.com" , "Roy, Patrick" , "shuah@kernel.org" , "steven.price@arm.com" , "suzuki.poulose@arm.com" , "vannapurve@google.com" , "vbabka@suse.cz" , "viro@zeniv.linux.org.uk" , "wei.w.wang@intel.com" , "will@kernel.org" , "willy@infradead.org" , "xiaoyao.li@intel.com" , "yilun.xu@intel.com" , "yuzenghui@huawei.com" Subject: Re: [PATCH v12 04/18] KVM: x86: Rename kvm->arch.has_private_mem to kvm->arch.supports_gmem Thread-Topic: [PATCH v12 04/18] KVM: x86: Rename kvm->arch.has_private_mem to kvm->arch.supports_gmem Thread-Index: AQHb5ZsRh+1QiHl0MkWMiF4y2LWD7A== Date: Wed, 25 Jun 2025 06:33:31 +0000 Message-ID: <20250625063328.28063-1-roypat@amazon.co.uk> References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 =0A= Hi Ackerley!=0A= =0A= On Tue, 2025-06-24 at 21:51 +0100, Ackerley Tng wrote:> Sean Christopherson= writes:=0A= > =0A= =0A= [...]=0A= =0A= >> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_= host.h=0A= >> index 3d69da6d2d9e..4bc50c1e21bd 100644=0A= >> --- a/arch/x86/include/asm/kvm_host.h=0A= >> +++ b/arch/x86/include/asm/kvm_host.h=0A= >> @@ -1341,7 +1341,7 @@ struct kvm_arch {=0A= >> unsigned int indirect_shadow_pages;=0A= >> u8 mmu_valid_gen;=0A= >> u8 vm_type;=0A= >> - bool has_private_mem;=0A= >> + bool supports_gmem;=0A= >> bool has_protected_state;=0A= >> bool pre_fault_allowed;=0A= >> struct hlist_head mmu_page_hash[KVM_NUM_MMU_PAGES];=0A= >> @@ -2270,7 +2270,7 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_fo= rced_root_level,=0A= >>=0A= >>=0A= >> #ifdef CONFIG_KVM_GMEM=0A= >> -#define kvm_arch_supports_gmem(kvm) ((kvm)->arch.has_private_mem)=0A= >> +#define kvm_arch_supports_gmem(kvm) ((kvm)->arch.supports_gmem)=0A= >> #else=0A= >> #define kvm_arch_supports_gmem(kvm) false=0A= >> #endif=0A= >> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c=0A= >> index e7ecf089780a..c4e10797610c 100644=0A= >> --- a/arch/x86/kvm/mmu/mmu.c=0A= >> +++ b/arch/x86/kvm/mmu/mmu.c=0A= >> @@ -3488,7 +3488,7 @@ static bool page_fault_can_be_fast(struct kvm *kvm= , struct kvm_page_fault *fault=0A= >> * on RET_PF_SPURIOUS until the update completes, or an actual spu= rious=0A= >> * case might go down the slow path. Either case will resolve itse= lf.=0A= >> */=0A= >> - if (kvm->arch.has_private_mem &&=0A= >> + if (kvm->arch.supports_gmem &&=0A= >> fault->is_private !=3D kvm_mem_is_private(kvm, fault->gfn))=0A= >> return false;=0A= >>=0A= > =0A= > This check should remain as a check on has_private_mem.=0A= > =0A= > If the VM supports private memory, skip fast page faults on fault type=0A= > and KVM memory privacy status mismatches.=0A= =0A= ...=0A= =0A= > Patrick, Nikita, am I right that for KVM_X86_DEFAULT_VM to work with=0A= > mmap-able guest_memfd, the usage in page_fault_can_be_fast() need not be= =0A= > updated, and that patch 10/18 in this series will be sufficient?=0A= =0A= Yeah, since KVM_X86_DEFAULT_VM does not and won't ever (?) support private= =0A= memory in guest_memfd (e.g. it always has to be used in all-shared mode) fr= om=0A= my understanding, the fault->is_private !=3D kvm_mem_is_private(kvm, fault-= >gfn))=0A= check should never succeed anyway. kvm_mem_is_private() will always return= =0A= false, and fault->is_private should always be false, too (unless the guest = does=0A= something it should not be doing, and even then the worst case is that we w= on't=0A= be handling this weirdness "fast").=0A= =0A= In my testing with earlier iterations of this series where=0A= page_fault_can_be_fast() was untouched I also never saw any problems relate= d to=0A= page faults on x86.=0A= =0A= Best, =0A= Patrick=0A=