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AJvYcCUqmuMV97RYJ/OFFUIXH/hTTjHhvzhlBjQ+edjIrKHWdyZ6zpjZtgeE0Zv6e9A7DoSENeeQx/I=@lists.linux.dev X-Gm-Message-State: AOJu0YyU3kN3Fq4xAHQMidDEWO6LSnTXTzzn0akbhpj9UN2McT8wimid VEVXhKQbdrOcuKzF1rp2wPVq7IoQra+4SgZGPUV1zrpqpReJEDAJ4QbT8Y7YX2zU+Cb0j5fX2vd ZcDdkbA== X-Google-Smtp-Source: AGHT+IE/cOKwq4Fz42CXevBf86/8AcgfZ4Shrse64gwOZtr6yxqQauczM06pGk5soclLR2YvbV9vIqjBOj4= X-Received: from pfbhd13.prod.google.com ([2002:a05:6a00:658d:b0:748:f98a:d97b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a20:7d9f:b0:232:1be:1e09 with SMTP id adf61e73a8af0-237d7545cf7mr36104602637.34.1753116472317; Mon, 21 Jul 2025 09:47:52 -0700 (PDT) Date: Mon, 21 Jul 2025 09:47:50 -0700 In-Reply-To: <20250717162731.446579-14-tabba@google.com> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-14-tabba@google.com> Message-ID: Subject: Re: [PATCH v15 13/21] KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory From: Sean Christopherson To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev, pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, xiaoyao.li@intel.com, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com Content-Type: text/plain; charset="us-ascii" On Thu, Jul 17, 2025, Fuad Tabba wrote: > From: Ackerley Tng > > Update the KVM MMU fault handler to service guest page faults > for memory slots backed by guest_memfd with mmap support. For such > slots, the MMU must always fault in pages directly from guest_memfd, > bypassing the host's userspace_addr. > > This ensures that guest_memfd-backed memory is always handled through > the guest_memfd specific faulting path, regardless of whether it's for > private or non-private (shared) use cases. > > Additionally, rename kvm_mmu_faultin_pfn_private() to > kvm_mmu_faultin_pfn_gmem(), as this function is now used to fault in > pages from guest_memfd for both private and non-private memory, > accommodating the new use cases. > > Co-developed-by: David Hildenbrand > Signed-off-by: David Hildenbrand > Signed-off-by: Ackerley Tng > Co-developed-by: Fuad Tabba > Signed-off-by: Fuad Tabba > --- > arch/x86/kvm/mmu/mmu.c | 13 +++++++++---- > 1 file changed, 9 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 94be15cde6da..ad5f337b496c 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4511,8 +4511,8 @@ static void kvm_mmu_finish_page_fault(struct kvm_vcpu *vcpu, > r == RET_PF_RETRY, fault->map_writable); > } > > -static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu, > - struct kvm_page_fault *fault) > +static int kvm_mmu_faultin_pfn_gmem(struct kvm_vcpu *vcpu, > + struct kvm_page_fault *fault) > { > int max_order, r; > > @@ -4536,13 +4536,18 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu, > return RET_PF_CONTINUE; > } > > +static bool fault_from_gmem(struct kvm_page_fault *fault) Drop the helper. It has exactly one caller, and it makes the code *harder* to read, e.g. raises the question of what "from gmem" even means. If a separate series follows and needs/justifies this helper, then it can/should be added then. > +{ > + return fault->is_private || kvm_memslot_is_gmem_only(fault->slot); > +} > + > static int __kvm_mmu_faultin_pfn(struct kvm_vcpu *vcpu, > struct kvm_page_fault *fault) > { > unsigned int foll = fault->write ? FOLL_WRITE : 0; > > - if (fault->is_private) > - return kvm_mmu_faultin_pfn_private(vcpu, fault); > + if (fault_from_gmem(fault)) > + return kvm_mmu_faultin_pfn_gmem(vcpu, fault); > > foll |= FOLL_NOWAIT; > fault->pfn = __kvm_faultin_pfn(fault->slot, fault->gfn, foll, > -- > 2.50.0.727.gbf7dc18ff4-goog >