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Wed, 12 Mar 2025 10:58:33 -0700 (PDT) Date: Wed, 12 Mar 2025 17:58:17 +0000 In-Reply-To: <20250312175824.1809636-1-tabba@google.com> Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20250312175824.1809636-1-tabba@google.com> X-Mailer: git-send-email 2.49.0.rc0.332.g42c0ae87b1-goog Message-ID: <20250312175824.1809636-5-tabba@google.com> Subject: [PATCH v6 04/10] KVM: guest_memfd: Allow host to map guest_memfd() pages From: Fuad Tabba To: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org 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, tabba@google.com Add support for mmap() and fault() for guest_memfd backed memory in the host for VMs that support in-place conversion between shared and private. To that end, this patch adds the ability to check whether the VM type supports in-place conversion, and only allows mapping its memory if that's the case. Also add the KVM capability KVM_CAP_GMEM_SHARED_MEM, which indicates that the VM supports shared memory in guest_memfd, or that the host can create VMs that support shared memory. Supporting shared memory implies that memory can be mapped when shared with the host. This is controlled by the KVM_GMEM_SHARED_MEM configuration option. Signed-off-by: Fuad Tabba --- include/linux/kvm_host.h | 11 +++++ include/uapi/linux/kvm.h | 1 + virt/kvm/guest_memfd.c | 102 +++++++++++++++++++++++++++++++++++++++ virt/kvm/kvm_main.c | 4 ++ 4 files changed, 118 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 3ad0719bfc4f..601bbcaa5e41 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -728,6 +728,17 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) } #endif +/* + * Arch code must define kvm_arch_gmem_supports_shared_mem if support for + * private memory is enabled and it supports in-place shared/private conversion. + */ +#if !defined(kvm_arch_gmem_supports_shared_mem) && !IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM) +static inline bool kvm_arch_gmem_supports_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 45e6d8fca9b9..117937a895da 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -929,6 +929,7 @@ struct kvm_enable_cap { #define KVM_CAP_PRE_FAULT_MEMORY 236 #define KVM_CAP_X86_APIC_BUS_CYCLES_NS 237 #define KVM_CAP_X86_GUEST_MODE 238 +#define KVM_CAP_GMEM_SHARED_MEM 239 struct kvm_irq_routing_irqchip { __u32 irqchip; diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 5fc414becae5..eea44e003ed1 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -320,7 +320,109 @@ 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 folio_offset_is_shared(const struct folio *folio, struct file *file, pgoff_t index) +{ + struct kvm_gmem *gmem = file->private_data; + + VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio); + + /* For now, VMs that support shared memory share all their memory. */ + return kvm_arch_gmem_supports_shared_mem(gmem->kvm); +} + +static vm_fault_t kvm_gmem_fault(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 (!folio_offset_is_shared(folio, vmf->vma->vm_file, vmf->pgoff)) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + /* + * Shared folios would not be marked as "guestmem" so far, and we only + * expect shared folios at this point. + */ + if (WARN_ON_ONCE(folio_test_guestmem(folio))) { + ret = VM_FAULT_SIGBUS; + goto out_folio; + } + + /* No support for huge pages. */ + 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); + + return ret; +} + +static const struct vm_operations_struct kvm_gmem_vm_ops = { + .fault = kvm_gmem_fault, +}; + +static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) +{ + struct kvm_gmem *gmem = file->private_data; + + if (!kvm_arch_gmem_supports_shared_mem(gmem->kvm)) + return -ENODEV; + + if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) != + (VM_SHARED | VM_MAYSHARE)) { + return -EINVAL; + } + + file_accessed(file); + vm_flags_set(vma, VM_DONTDUMP); + 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, diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index ba0327e2d0d3..38f0f402ea46 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4830,6 +4830,10 @@ static int kvm_vm_ioctl_check_extension_generic(struct kvm *kvm, long arg) #ifdef CONFIG_KVM_PRIVATE_MEM case KVM_CAP_GUEST_MEMFD: return !kvm || kvm_arch_has_private_mem(kvm); +#endif +#ifdef CONFIG_KVM_GMEM_SHARED_MEM + case KVM_CAP_GMEM_SHARED_MEM: + return !kvm || kvm_arch_gmem_supports_shared_mem(kvm); #endif default: break;