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b=WeLHgmXx0r97gR/zn1eWenIdriuOSpYVj9Enitmu+wk6hPYUCHXPbtDMke+K2iZ8CfIEli L2PPPUlUHtpcnh+fY+glHgeelj+WuvAribXpZM+k/8swY851tIbGWUVGWzbcfzmko35xvp bSykaR5ROyJfWZ7ZJwWd2TTVDWbPsEs= Date: Tue, 22 Jul 2025 20:31:34 +0800 MIME-Version: 1.0 Subject: Re: [PATCH v15 16/21] KVM: arm64: Handle guest_memfd-backed guest page faults Content-Language: en-US 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: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-17-tabba@google.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Kunwu Chan In-Reply-To: <20250717162731.446579-17-tabba@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: EFD53A0002 X-Stat-Signature: 6uc791ie4pz51zw7m39qan66ht41wggb X-HE-Tag: 1753187551-798053 X-HE-Meta: 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 SEB/fkqE 9R1lxhviD5AvKqW+Rpz7Bmham9GkTBMVqVNYKY/YmtdZRSJ9Qg35yaVZ6imHkM2ETb15O3YHKaF3pYvK9QlXjsCeGYK7l5GV3kRhLy1I74jpblDyscaEE1jizgzacadOjJsT90o7tXsKrkGEFhbz8aTFBKpfgTncuJ5ne86GZa22FgAPYAsTH4U2I9wgeE+WOJCXU8kbTEhkMUvONe++2RHNW2rqGx6wrElUy0RuOOsnyVczdg1CUtop3idqZXx6uWIwBXVHY18tfZIiP7JoKKMii602PpPJ/uswEyRCOqY8mVMu3AVKwyou/orGS6CT9pr+Jt90XqNMxhA64zOtif/OZ5krNMzSX/mLREs9bdSTAJQnQLkhKIc3KFRNE63QUszsh//Xx773n2145M18FenWBwLLgqBUBga7B 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: On 2025/7/18 00:27, Fuad Tabba wrote: > Add arm64 architecture support for handling guest page faults on memory > slots backed by guest_memfd. > > This change introduces a new function, gmem_abort(), which encapsulates > the fault handling logic specific to guest_memfd-backed memory. The > kvm_handle_guest_abort() entry point is updated to dispatch to > gmem_abort() when a fault occurs on a guest_memfd-backed memory slot (as > determined by kvm_slot_has_gmem()). > > Until guest_memfd gains support for huge pages, the fault granule for > these memory regions is restricted to PAGE_SIZE. Since huge pages are not currently supported, would it be more friendly to define  sth like "#define GMEM_PAGE_GRANULE PAGE_SIZE" at the top (rather than hardcoding PAGE_SIZE)  and make it easier to switch to huge page support later? > Reviewed-by: Gavin Shan > Reviewed-by: James Houghton > Signed-off-by: Fuad Tabba > --- > arch/arm64/kvm/mmu.c | 86 ++++++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 83 insertions(+), 3 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index b3eacb400fab..8c82df80a835 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1512,6 +1512,82 @@ 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 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; > + unsigned long mmu_seq; > + struct page *page; > + struct kvm *kvm = vcpu->kvm; > + void *memcache; > + kvm_pfn_t pfn; > + gfn_t gfn; > + int ret; > + > + ret = prepare_mmu_memcache(vcpu, true, &memcache); > + if (ret) > + return ret; > + > + if (nested) > + gfn = kvm_s2_trans_output(nested) >> PAGE_SHIFT; > + else > + gfn = fault_ipa >> PAGE_SHIFT; > + > + write_fault = kvm_is_write_fault(vcpu); > + exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu); > + > + VM_WARN_ON_ONCE(write_fault && exec_fault); > + > + mmu_seq = kvm->mmu_invalidate_seq; > + /* Pairs with the smp_wmb() in kvm_mmu_invalidate_end(). */ > + smp_rmb(); > + > + 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; > + } > + > + writable = !(memslot->flags & KVM_MEM_READONLY); > + > + 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 (mmu_invalidate_retry(kvm, mmu_seq)) { > + ret = -EAGAIN; > + goto out_unlock; > + } > + > + ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, fault_ipa, PAGE_SIZE, > + __pfn_to_phys(pfn), prot, > + memcache, flags); > + > +out_unlock: > + 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, > @@ -1536,7 +1612,7 @@ 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); > @@ -1961,8 +2037,12 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu) > VM_WARN_ON_ONCE(kvm_vcpu_trap_is_permission_fault(vcpu) && > !write_fault && !kvm_vcpu_trap_is_exec_fault(vcpu)); > > - 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: LGTM! -- Thanks, Kunwu.Chan(Tao.Chan)