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AJvYcCXdKFxcyMtnWzWsJI6jRIfkyYXMhBiPJKnFM9MyRDycEcePSaL6bZSMpsrF2UcMfDs406MRVu7FqA==@kvack.org X-Gm-Message-State: AOJu0YwNswI83NbZHk054VjJm2rKLdzfxPhpHmOeZc0/wTMt9xHvGAs4 0P5GNEtO3mpoA8Hm8PAyef8Y9NsyUKkmpaantHiu/ERlRpVXcbOyLcVnUFYGL9jxUm3NE6RXWjU PD6s7wKAGE75ep2x5U+0tJw== X-Google-Smtp-Source: AGHT+IHh48dnUNnPj0jVGNHdz5yY1x34jSSkfzq+soIDIBQwcVrmJ1EYujTkYpGapSQ59E8CIvectH0AL1mRigl+MA== X-Received: from pjtq3.prod.google.com ([2002:a17:90a:c103:b0:2ff:8471:8e53]) (user=ackerleytng job=prod-delivery.src-stubby-dispatcher) by 2002:a17:90b:5590:b0:2ea:7cd5:4ad6 with SMTP id 98e67ed59e1d1-30e2e633695mr794444a91.32.1747161469403; Tue, 13 May 2025 11:37:49 -0700 (PDT) Date: Tue, 13 May 2025 11:37:48 -0700 In-Reply-To: <20250513163438.3942405-8-tabba@google.com> (message from Fuad Tabba on Tue, 13 May 2025 17:34:28 +0100) Mime-Version: 1.0 Message-ID: Subject: Re: [PATCH v9 07/17] KVM: guest_memfd: Allow host to map guest_memfd() pages From: Ackerley Tng To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, 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, 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, tabba@google.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: c9mzbs9fh1srm7xdzs4dyii3tf7g1ssr X-Rspam-User: X-Rspamd-Queue-Id: D347BA0002 X-Rspamd-Server: rspam06 X-HE-Tag: 1747161470-782583 X-HE-Meta: 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 szghgOlR 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 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: Fuad Tabba writes: > This patch enables support for shared memory in guest_memfd, including > mapping that memory at the host userspace. This support is gated by the > configuration option KVM_GMEM_SHARED_MEM, and toggled by the guest_memfd > flag GUEST_MEMFD_FLAG_SUPPORT_SHARED, which can be set when creating a > guest_memfd instance. > > Co-developed-by: Ackerley Tng > Signed-off-by: Ackerley Tng > Signed-off-by: Fuad Tabba > --- > arch/x86/include/asm/kvm_host.h | 10 ++++ > include/linux/kvm_host.h | 13 +++++ > include/uapi/linux/kvm.h | 1 + > virt/kvm/Kconfig | 5 ++ > virt/kvm/guest_memfd.c | 88 +++++++++++++++++++++++++++++++++ > 5 files changed, 117 insertions(+) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index 709cc2a7ba66..f72722949cae 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -2255,8 +2255,18 @@ void kvm_configure_mmu(bool enable_tdp, int tdp_forced_root_level, > > #ifdef CONFIG_KVM_GMEM > #define kvm_arch_supports_gmem(kvm) ((kvm)->arch.supports_gmem) > + > +/* > + * CoCo VMs with hardware support that use guest_memfd only for backing private > + * memory, e.g., TDX, cannot use guest_memfd with userspace mapping enabled. > + */ > +#define kvm_arch_vm_supports_gmem_shared_mem(kvm) \ > + (IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM) && \ > + ((kvm)->arch.vm_type == KVM_X86_SW_PROTECTED_VM || \ > + (kvm)->arch.vm_type == KVM_X86_DEFAULT_VM)) > #else > #define kvm_arch_supports_gmem(kvm) false > +#define kvm_arch_vm_supports_gmem_shared_mem(kvm) false > #endif > > #define kvm_arch_has_readonly_mem(kvm) (!(kvm)->arch.has_protected_state) > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index ae70e4e19700..2ec89c214978 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -729,6 +729,19 @@ static inline bool kvm_arch_supports_gmem(struct kvm *kvm) > } > #endif > > +/* > + * Returns true if this VM supports shared mem in guest_memfd. > + * > + * Arch code must define kvm_arch_vm_supports_gmem_shared_mem if support for > + * guest_memfd is enabled. > + */ > +#if !defined(kvm_arch_vm_supports_gmem_shared_mem) && !IS_ENABLED(CONFIG_KVM_GMEM) > +static inline bool kvm_arch_vm_supports_gmem_shared_mem(struct kvm *kvm) > +{ > + return false; > +} > +#endif > + > #ifndef kvm_arch_has_readonly_mem > static inline bool kvm_arch_has_readonly_mem(struct kvm *kvm) > { > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h > index b6ae8ad8934b..9857022a0f0c 100644 > --- a/include/uapi/linux/kvm.h > +++ b/include/uapi/linux/kvm.h > @@ -1566,6 +1566,7 @@ struct kvm_memory_attributes { > #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3) > > #define KVM_CREATE_GUEST_MEMFD _IOWR(KVMIO, 0xd4, struct kvm_create_guest_memfd) > +#define GUEST_MEMFD_FLAG_SUPPORT_SHARED (1UL << 0) > > struct kvm_create_guest_memfd { > __u64 size; > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index 559c93ad90be..f4e469a62a60 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -128,3 +128,8 @@ config HAVE_KVM_ARCH_GMEM_PREPARE > config HAVE_KVM_ARCH_GMEM_INVALIDATE > bool > depends on KVM_GMEM > + > +config KVM_GMEM_SHARED_MEM > + select KVM_GMEM > + bool > + prompt "Enables in-place shared memory for guest_memfd" > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 6db515833f61..8e6d1866b55e 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -312,7 +312,88 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn) > return gfn - slot->base_gfn + slot->gmem.pgoff; > } > > +#ifdef CONFIG_KVM_GMEM_SHARED_MEM > + > +static bool kvm_gmem_supports_shared(struct inode *inode) > +{ > + uint64_t flags = (uint64_t)inode->i_private; > + > + return flags & GUEST_MEMFD_FLAG_SUPPORT_SHARED; > +} > + > +static vm_fault_t kvm_gmem_fault_shared(struct vm_fault *vmf) > +{ > + struct inode *inode = file_inode(vmf->vma->vm_file); > + struct folio *folio; > + vm_fault_t ret = VM_FAULT_LOCKED; > + > + filemap_invalidate_lock_shared(inode->i_mapping); > + > + folio = kvm_gmem_get_folio(inode, vmf->pgoff); > + if (IS_ERR(folio)) { > + int err = PTR_ERR(folio); > + > + if (err == -EAGAIN) > + ret = VM_FAULT_RETRY; > + else > + ret = vmf_error(err); > + > + goto out_filemap; > + } > + > + if (folio_test_hwpoison(folio)) { > + ret = VM_FAULT_HWPOISON; > + goto out_folio; > + } > + > + if (WARN_ON_ONCE(folio_test_large(folio))) { > + ret = VM_FAULT_SIGBUS; > + goto out_folio; > + } > + > + if (!folio_test_uptodate(folio)) { > + clear_highpage(folio_page(folio, 0)); > + kvm_gmem_mark_prepared(folio); > + } > + > + vmf->page = folio_file_page(folio, vmf->pgoff); > + > +out_folio: > + if (ret != VM_FAULT_LOCKED) { > + folio_unlock(folio); > + folio_put(folio); > + } > + > +out_filemap: > + filemap_invalidate_unlock_shared(inode->i_mapping); Do we need to hold the filemap_invalidate_lock while zeroing? Would holding the folio lock be enough? > + > + return ret; > +} > + > +static const struct vm_operations_struct kvm_gmem_vm_ops = { > + .fault = kvm_gmem_fault_shared, > +}; > + > +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) > +{ > + if (!kvm_gmem_supports_shared(file_inode(file))) > + return -ENODEV; > + > + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) != > + (VM_SHARED | VM_MAYSHARE)) { > + return -EINVAL; > + } > + > + vma->vm_ops = &kvm_gmem_vm_ops; > + > + return 0; > +} > +#else > +#define kvm_gmem_mmap NULL > +#endif /* CONFIG_KVM_GMEM_SHARED_MEM */ > + > static struct file_operations kvm_gmem_fops = { > + .mmap = kvm_gmem_mmap, > .open = generic_file_open, > .release = kvm_gmem_release, > .fallocate = kvm_gmem_fallocate, > @@ -463,6 +544,9 @@ int kvm_gmem_create(struct kvm *kvm, struct kvm_create_guest_memfd *args) > u64 flags = args->flags; > u64 valid_flags = 0; > > + if (kvm_arch_vm_supports_gmem_shared_mem(kvm)) > + valid_flags |= GUEST_MEMFD_FLAG_SUPPORT_SHARED; > + > if (flags & ~valid_flags) > return -EINVAL; > > @@ -501,6 +585,10 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot, > offset + size > i_size_read(inode)) > goto err; > > + if (kvm_gmem_supports_shared(inode) && > + !kvm_arch_vm_supports_gmem_shared_mem(kvm)) > + goto err; > + > filemap_invalidate_lock(inode->i_mapping); > > start = offset >> PAGE_SHIFT;