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Mon, 09 Jun 2025 00:04:50 -0700 (PDT) MIME-Version: 1.0 References: <20250605153800.557144-1-tabba@google.com> <20250605153800.557144-15-tabba@google.com> <3d9a15ff-fbb2-4e9a-b97b-c0e40eb23043@redhat.com> In-Reply-To: <3d9a15ff-fbb2-4e9a-b97b-c0e40eb23043@redhat.com> From: Fuad Tabba Date: Mon, 9 Jun 2025 08:04:14 +0100 X-Gm-Features: AX0GCFsczmm-1bXIlO1Jg10AW7DfDInPlMUvClXpf3ptG11SFLUaa_qGeD9GUQs Message-ID: Subject: Re: [PATCH v11 14/18] KVM: arm64: Handle guest_memfd-backed guest page faults To: Gavin Shan 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 Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 46961C000E X-Stat-Signature: tmzxdgf9ph73bzqewq7ya4tb85s7ht1m X-Rspam-User: X-HE-Tag: 1749452692-573240 X-HE-Meta: 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 tf2phb0s 0V6tP7jJSZbJKV0AHIFPgTqw5Ra1fxozMcRq9xOtGwzRVyiEx0pa1LQYtHQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Gavin, On Mon, 9 Jun 2025 at 05:08, Gavin Shan wrote: > > 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()? :-) 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! /fuad > 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: >