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[175.34.62.5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7482af7b606sm5481711b3a.67.2025.06.09.02.06.15 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Jun 2025 02:06:33 -0700 (PDT) Message-ID: Date: Mon, 9 Jun 2025 19:06:13 +1000 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v11 14/18] KVM: arm64: Handle guest_memfd-backed guest page faults 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, seanjc@google.com, 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 References: <20250605153800.557144-1-tabba@google.com> <20250605153800.557144-15-tabba@google.com> <3d9a15ff-fbb2-4e9a-b97b-c0e40eb23043@redhat.com> Content-Language: en-US From: Gavin Shan In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Fuad, On 6/9/25 5:04 PM, Fuad Tabba wrote: > On Mon, 9 Jun 2025 at 05:08, Gavin Shan wrote: >> >> On 6/6/25 1:37 AM, Fuad Tabba wrote: >>> Add arm64 support for handling guest page faults on guest_memfd backed >>> memslots. Until guest_memfd supports huge pages, the fault granule is >>> restricted to PAGE_SIZE. >>> >>> Signed-off-by: Fuad Tabba >>> --- >>> arch/arm64/kvm/mmu.c | 93 ++++++++++++++++++++++++++++++++++++++++++-- >>> 1 file changed, 90 insertions(+), 3 deletions(-) >>> >> >> One comment below. Otherwise, it looks good to me. >> >> Reviewed-by: Gavin Shan >> >>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c >>> index ce80be116a30..f14925fe6144 100644 >>> --- a/arch/arm64/kvm/mmu.c >>> +++ b/arch/arm64/kvm/mmu.c >>> @@ -1508,6 +1508,89 @@ static void adjust_nested_fault_perms(struct kvm_s2_trans *nested, >>> *prot |= kvm_encode_nested_level(nested); >>> } >>> >>> +#define KVM_PGTABLE_WALK_MEMABORT_FLAGS (KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED) >>> + >>> +static int gmem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>> + struct kvm_s2_trans *nested, >>> + struct kvm_memory_slot *memslot, bool is_perm) >>> +{ >>> + bool logging, write_fault, exec_fault, writable; >>> + enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_MEMABORT_FLAGS; >>> + enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R; >>> + struct kvm_pgtable *pgt = vcpu->arch.hw_mmu->pgt; >>> + struct page *page; >>> + struct kvm *kvm = vcpu->kvm; >>> + void *memcache; >>> + kvm_pfn_t pfn; >>> + gfn_t gfn; >>> + int ret; >>> + >>> + ret = prepare_mmu_memcache(vcpu, !is_perm, &memcache); >>> + if (ret) >>> + return ret; >>> + >>> + if (nested) >>> + gfn = kvm_s2_trans_output(nested) >> PAGE_SHIFT; >>> + else >>> + gfn = fault_ipa >> PAGE_SHIFT; >>> + >>> + logging = memslot_is_logging(memslot); >>> + write_fault = kvm_is_write_fault(vcpu); >>> + exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu); >>> + >>> + if (write_fault && exec_fault) { >>> + kvm_err("Simultaneous write and execution fault\n"); >>> + return -EFAULT; >>> + } >>> + >>> + if (is_perm && !write_fault && !exec_fault) { >>> + kvm_err("Unexpected L2 read permission error\n"); >>> + return -EFAULT; >>> + } >>> + >>> + ret = kvm_gmem_get_pfn(kvm, memslot, gfn, &pfn, &page, NULL); >>> + if (ret) { >>> + kvm_prepare_memory_fault_exit(vcpu, fault_ipa, PAGE_SIZE, >>> + write_fault, exec_fault, false); >>> + return ret; >>> + } >>> + >> >> -EFAULT or -EHWPOISON shall be returned, as documented in virt/kvm/api.rst. Besides, >> kvm_send_hwpoison_signal() should be executed when -EHWPOISON is returned from >> kvm_gmem_get_pfn()? :-) > > This is a bit different since we don't have a VMA. Refer to the discussion here: > > https://lore.kernel.org/all/20250514212653.1011484-1-jthoughton@google.com/ > Thanks for the pointer. You're right that we don't have VMA here. To return the 'ret' to userspace seems the practical way to have here. Thanks, Gavin >> >>> + writable = !(memslot->flags & KVM_MEM_READONLY) && >>> + (!logging || write_fault); >>> + >>> + if (nested) >>> + adjust_nested_fault_perms(nested, &prot, &writable); >>> + >>> + if (writable) >>> + prot |= KVM_PGTABLE_PROT_W; >>> + >>> + if (exec_fault || >>> + (cpus_have_final_cap(ARM64_HAS_CACHE_DIC) && >>> + (!nested || kvm_s2_trans_executable(nested)))) >>> + prot |= KVM_PGTABLE_PROT_X; >>> + >>> + kvm_fault_lock(kvm); >>> + if (is_perm) { >>> + /* >>> + * Drop the SW bits in favour of those stored in the >>> + * PTE, which will be preserved. >>> + */ >>> + prot &= ~KVM_NV_GUEST_MAP_SZ; >>> + ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, fault_ipa, prot, flags); >>> + } else { >>> + ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault_ipa, PAGE_SIZE, >>> + __pfn_to_phys(pfn), prot, >>> + memcache, flags); >>> + } >>> + kvm_release_faultin_page(kvm, page, !!ret, writable); >>> + kvm_fault_unlock(kvm); >>> + >>> + if (writable && !ret) >>> + mark_page_dirty_in_slot(kvm, memslot, gfn); >>> + >>> + return ret != -EAGAIN ? ret : 0; >>> +} >>> + >>> static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>> struct kvm_s2_trans *nested, >>> struct kvm_memory_slot *memslot, unsigned long hva, >>> @@ -1532,7 +1615,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, >>> enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R; >>> struct kvm_pgtable *pgt; >>> struct page *page; >>> - enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_HANDLE_FAULT | KVM_PGTABLE_WALK_SHARED; >>> + enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_MEMABORT_FLAGS; >>> >>> if (fault_is_perm) >>> fault_granule = kvm_vcpu_trap_get_perm_fault_granule(vcpu); >>> @@ -1959,8 +2042,12 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu) >>> goto out_unlock; >>> } >>> >>> - ret = user_mem_abort(vcpu, fault_ipa, nested, memslot, hva, >>> - esr_fsc_is_permission_fault(esr)); >>> + if (kvm_slot_has_gmem(memslot)) >>> + ret = gmem_abort(vcpu, fault_ipa, nested, memslot, >>> + esr_fsc_is_permission_fault(esr)); >>> + else >>> + ret = user_mem_abort(vcpu, fault_ipa, nested, memslot, hva, >>> + esr_fsc_is_permission_fault(esr)); >>> if (ret == 0) >>> ret = 1; >>> out: >> >