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X-CSE-ConnectionGUID: y6S9jiG6TRiyMNusiJ2ZhQ== X-CSE-MsgGUID: 0uwSSu0sQZ+g/cmWz0IXgg== X-IronPort-AV: E=McAfee;i="6800,10657,11495"; a="55231378" X-IronPort-AV: E=Sophos;i="6.16,320,1744095600"; d="scan'208";a="55231378" Received: from orviesa006.jf.intel.com ([10.64.159.146]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2025 23:09:44 -0700 X-CSE-ConnectionGUID: b3Qe9VFRT1yDBJGJPtpzNw== X-CSE-MsgGUID: xpob/a9xSH2SyoR3DNf2uA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,320,1744095600"; d="scan'208";a="157367080" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.247.1]) ([10.124.247.1]) by orviesa006-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2025 23:09:27 -0700 Message-ID: <9f8bd84d-6386-4e3c-802b-de598b8ac0c2@intel.com> Date: Fri, 18 Jul 2025 14:09:24 +0800 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v15 13/21] KVM: x86/mmu: Handle guest page faults for guest_memfd with shared memory To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, 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 References: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-14-tabba@google.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20250717162731.446579-14-tabba@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/18/2025 12:27 AM, 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 Reviewed-by: Xiaoyao Li Note to myself: After this patch, it looks possible that kvm_mmu_prepare_memory_fault_exit() in kvm_mmu_faultin_pfn_gmem() might be triggered for guest_memfd with mmap support, though I'm not sure if there is real case to trigger it. This requires some change in QEMU when it adds support for guest_memfd mmap support, since current QEMU handles KVM_EXIT_MEMORY_FAULT by always converting the memory attribute. > --- > 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) > +{ > + 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,