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[175.34.62.5]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7482af382fcsm4806740b3a.28.2025.06.08.21.08.32 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 08 Jun 2025 21:08:52 -0700 (PDT) Message-ID: <3d9a15ff-fbb2-4e9a-b97b-c0e40eb23043@redhat.com> Date: Mon, 9 Jun 2025 14:08:30 +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 , 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, 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> Content-Language: en-US From: Gavin Shan In-Reply-To: <20250605153800.557144-15-tabba@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Hi Fuad, 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()? :-) 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: