On Thu, Oct 10, 2024 at 09:59:23AM +0100, Fuad Tabba wrote: > Add support for mmap() and fault() for guest_memfd in the host. > The ability to fault in a guest page is contingent on that page > being shared with the host. > > The guest_memfd PRIVATE memory attribute is not used for two > reasons. First because it reflects the userspace expectation for > that memory location, and therefore can be toggled by userspace. > The second is, although each guest_memfd file has a 1:1 binding > with a KVM instance, the plan is to allow multiple files per > inode, e.g. to allow intra-host migration to a new KVM instance, > without destroying guest_memfd. > > The mapping is restricted to only memory explicitly shared with > the host. KVM checks that the host doesn't have any mappings for > private memory via the folio's refcount. To avoid races between > paths that check mappability and paths that check whether the > host has any mappings (via the refcount), the folio lock is held > in while either check is being performed. > > This new feature is gated with a new configuration option, > CONFIG_KVM_GMEM_MAPPABLE. > > Co-developed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx> > Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx> > Co-developed-by: Elliot Berman <quic_eberman@xxxxxxxxxxx> > Signed-off-by: Elliot Berman <quic_eberman@xxxxxxxxxxx> > Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx> > > --- > > Note that the functions kvm_gmem_is_mapped(), > kvm_gmem_set_mappable(), and int kvm_gmem_clear_mappable() are > not used in this patch series. They are intended to be used in > future patches [*], which check and toggle mapability when the > guest shares/unshares pages with the host. > > [*] https://android-kvm.googlesource.com/linux/+/refs/heads/tabba/guestmem-6.12-v3-pkvm > > --- > include/linux/kvm_host.h | 52 +++++++++++ > virt/kvm/Kconfig | 4 + > virt/kvm/guest_memfd.c | 185 +++++++++++++++++++++++++++++++++++++++ > virt/kvm/kvm_main.c | 138 +++++++++++++++++++++++++++++ > 4 files changed, 379 insertions(+) > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index acf85995b582..bda7fda9945e 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -2527,4 +2527,56 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, > struct kvm_pre_fault_memory *range); > #endif > > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > +bool kvm_gmem_is_mappable(struct kvm *kvm, gfn_t gfn, gfn_t end); > +bool kvm_gmem_is_mapped(struct kvm *kvm, gfn_t start, gfn_t end); > +int kvm_gmem_set_mappable(struct kvm *kvm, gfn_t start, gfn_t end); > +int kvm_gmem_clear_mappable(struct kvm *kvm, gfn_t start, gfn_t end); > +int kvm_slot_gmem_set_mappable(struct kvm_memory_slot *slot, gfn_t start, > + gfn_t end); > +int kvm_slot_gmem_clear_mappable(struct kvm_memory_slot *slot, gfn_t start, > + gfn_t end); > +bool kvm_slot_gmem_is_mappable(struct kvm_memory_slot *slot, gfn_t gfn); > +#else > +static inline bool kvm_gmem_is_mappable(struct kvm *kvm, gfn_t gfn, gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return false; > +} > +static inline bool kvm_gmem_is_mapped(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return false; > +} > +static inline int kvm_gmem_set_mappable(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return -EINVAL; > +} > +static inline int kvm_gmem_clear_mappable(struct kvm *kvm, gfn_t start, > + gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return -EINVAL; > +} > +static inline int kvm_slot_gmem_set_mappable(struct kvm_memory_slot *slot, > + gfn_t start, gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return -EINVAL; > +} > +static inline int kvm_slot_gmem_clear_mappable(struct kvm_memory_slot *slot, > + gfn_t start, gfn_t end) > +{ > + WARN_ON_ONCE(1); > + return -EINVAL; > +} > +static inline bool kvm_slot_gmem_is_mappable(struct kvm_memory_slot *slot, > + gfn_t gfn) > +{ > + WARN_ON_ONCE(1); > + return false; > +} > +#endif /* CONFIG_KVM_GMEM_MAPPABLE */ > + > #endif > diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig > index fd6a3010afa8..2cfcb0848e37 100644 > --- a/virt/kvm/Kconfig > +++ b/virt/kvm/Kconfig > @@ -120,3 +120,7 @@ config HAVE_KVM_ARCH_GMEM_PREPARE > config HAVE_KVM_ARCH_GMEM_INVALIDATE > bool > depends on KVM_PRIVATE_MEM > + > +config KVM_GMEM_MAPPABLE > + select KVM_PRIVATE_MEM > + bool > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index f414646c475b..df3a6f05a16e 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -370,7 +370,184 @@ static void kvm_gmem_init_mount(void) > kvm_gmem_mnt->mnt_flags |= MNT_NOEXEC; > } > > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > +static struct folio * > +__kvm_gmem_get_pfn(struct file *file, struct kvm_memory_slot *slot, > + gfn_t gfn, kvm_pfn_t *pfn, bool *is_prepared, > + int *max_order); > + > +static int gmem_set_mappable(struct inode *inode, pgoff_t start, pgoff_t end) > +{ > + struct xarray *mappable_offsets = &kvm_gmem_private(inode)->mappable_offsets; > + void *xval = xa_mk_value(true); > + pgoff_t i; > + bool r; > + > + filemap_invalidate_lock(inode->i_mapping); > + for (i = start; i < end; i++) { > + r = xa_err(xa_store(mappable_offsets, i, xval, GFP_KERNEL)); I think it might not be strictly necessary, > + if (r) > + break; > + } > + filemap_invalidate_unlock(inode->i_mapping); > + > + return r; > +} > + > +static int gmem_clear_mappable(struct inode *inode, pgoff_t start, pgoff_t end) > +{ > + struct xarray *mappable_offsets = &kvm_gmem_private(inode)->mappable_offsets; > + pgoff_t i; > + int r = 0; > + > + filemap_invalidate_lock(inode->i_mapping); > + for (i = start; i < end; i++) { > + struct folio *folio; > + > + /* > + * Holds the folio lock until after checking its refcount, > + * to avoid races with paths that fault in the folio. > + */ > + folio = kvm_gmem_get_folio(inode, i); We don't need to allocate the folio here. I think we can use folio = filemap_lock_folio(inode, i); if (!folio || WARN_ON_ONCE(IS_ERR(folio))) continue; > + if (WARN_ON_ONCE(IS_ERR(folio))) > + continue; > + > + /* > + * Check that the host doesn't have any mappings on clearing > + * the mappable flag, because clearing the flag implies that the > + * memory will be unshared from the host. Therefore, to maintain > + * the invariant that the host cannot access private memory, we > + * need to check that it doesn't have any mappings to that > + * memory before making it private. > + * > + * Two references are expected because of kvm_gmem_get_folio(). > + */ > + if (folio_ref_count(folio) > 2) If we'd like to be prepared for large folios, it should be folio_nr_pages(folio) + 1. > + r = -EPERM; > + else > + xa_erase(mappable_offsets, i); > + > + folio_put(folio); > + folio_unlock(folio); > + > + if (r) > + break; > + } > + filemap_invalidate_unlock(inode->i_mapping); > + > + return r; > +} > + > +static bool gmem_is_mappable(struct inode *inode, pgoff_t pgoff) > +{ > + struct xarray *mappable_offsets = &kvm_gmem_private(inode)->mappable_offsets; > + bool r; > + > + filemap_invalidate_lock_shared(inode->i_mapping); > + r = xa_find(mappable_offsets, &pgoff, pgoff, XA_PRESENT); > + filemap_invalidate_unlock_shared(inode->i_mapping); > + > + return r; > +} > + > +int kvm_slot_gmem_set_mappable(struct kvm_memory_slot *slot, gfn_t start, gfn_t end) > +{ > + struct inode *inode = file_inode(slot->gmem.file); > + pgoff_t start_off = slot->gmem.pgoff + start - slot->base_gfn; > + pgoff_t end_off = start_off + end - start; > + > + return gmem_set_mappable(inode, start_off, end_off); > +} > + > +int kvm_slot_gmem_clear_mappable(struct kvm_memory_slot *slot, gfn_t start, gfn_t end) > +{ > + struct inode *inode = file_inode(slot->gmem.file); > + pgoff_t start_off = slot->gmem.pgoff + start - slot->base_gfn; > + pgoff_t end_off = start_off + end - start; > + > + return gmem_clear_mappable(inode, start_off, end_off); > +} > + > +bool kvm_slot_gmem_is_mappable(struct kvm_memory_slot *slot, gfn_t gfn) > +{ > + struct inode *inode = file_inode(slot->gmem.file); > + unsigned long pgoff = slot->gmem.pgoff + gfn - slot->base_gfn; > + > + return gmem_is_mappable(inode, pgoff); > +} > + > +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; > + > + /* > + * Holds the folio lock until after checking whether it can be faulted > + * in, to avoid races with paths that change a folio's mappability. > + */ > + folio = kvm_gmem_get_folio(inode, vmf->pgoff); > + if (!folio) > + return VM_FAULT_SIGBUS; > + > + if (folio_test_hwpoison(folio)) { > + ret = VM_FAULT_HWPOISON; > + goto out; > + } > + > + if (!gmem_is_mappable(inode, vmf->pgoff)) { > + ret = VM_FAULT_SIGBUS; > + goto out; > + } > + > + if (!folio_test_uptodate(folio)) { > + unsigned long nr_pages = folio_nr_pages(folio); > + unsigned long i; > + > + for (i = 0; i < nr_pages; i++) > + clear_highpage(folio_page(folio, i)); > + > + folio_mark_uptodate(folio); > + } > + > + vmf->page = folio_file_page(folio, vmf->pgoff); > +out: > + if (ret != VM_FAULT_LOCKED) { > + folio_put(folio); > + folio_unlock(folio); > + } > + > + 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) > +{ > + 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 > +static int gmem_set_mappable(struct inode *inode, pgoff_t start, pgoff_t end) > +{ > + WARN_ON_ONCE(1); > + return -EINVAL; > +} > +#define kvm_gmem_mmap NULL > +#endif /* CONFIG_KVM_GMEM_MAPPABLE */ > + > static struct file_operations kvm_gmem_fops = { > + .mmap = kvm_gmem_mmap, > .open = generic_file_open, > .release = kvm_gmem_release, > .fallocate = kvm_gmem_fallocate, > @@ -557,6 +734,14 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) > goto err_gmem; > } > > + if (IS_ENABLED(CONFIG_KVM_GMEM_MAPPABLE)) { > + err = gmem_set_mappable(file_inode(file), 0, size >> PAGE_SHIFT); > + if (err) { > + fput(file); > + goto err_gmem; > + } > + } > + > kvm_get_kvm(kvm); > gmem->kvm = kvm; > xa_init(&gmem->bindings); > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 05cbb2548d99..aed9cf2f1685 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3263,6 +3263,144 @@ static int next_segment(unsigned long len, int offset) > return len; > } > > +#ifdef CONFIG_KVM_GMEM_MAPPABLE > +static bool __kvm_gmem_is_mappable(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + struct kvm_memslot_iter iter; > + > + lockdep_assert_held(&kvm->slots_lock); > + > + kvm_for_each_memslot_in_gfn_range(&iter, kvm_memslots(kvm), start, end) { > + struct kvm_memory_slot *memslot = iter.slot; > + gfn_t gfn_start, gfn_end, i; > + > + gfn_start = max(start, memslot->base_gfn); > + gfn_end = min(end, memslot->base_gfn + memslot->npages); > + if (WARN_ON_ONCE(gfn_start >= gfn_end)) > + continue; > + > + for (i = gfn_start; i < gfn_end; i++) { > + if (!kvm_slot_gmem_is_mappable(memslot, i)) > + return false; > + } > + } > + > + return true; > +} > + > +bool kvm_gmem_is_mappable(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + bool r; > + > + mutex_lock(&kvm->slots_lock); > + r = __kvm_gmem_is_mappable(kvm, start, end); > + mutex_unlock(&kvm->slots_lock); > + > + return r; > +} > + > +static bool kvm_gmem_is_pfn_mapped(struct kvm *kvm, struct kvm_memory_slot *memslot, gfn_t gfn_idx) > +{ > + struct page *page; > + bool is_mapped; > + kvm_pfn_t pfn; > + > + /* > + * Holds the folio lock until after checking its refcount, > + * to avoid races with paths that fault in the folio. > + */ > + if (WARN_ON_ONCE(kvm_gmem_get_pfn_locked(kvm, memslot, gfn_idx, &pfn, NULL))) > + return false; > + > + page = pfn_to_page(pfn); > + > + /* Two references are expected because of kvm_gmem_get_pfn_locked(). */ > + is_mapped = page_ref_count(page) > 2; > + > + put_page(page); > + unlock_page(page); > + > + return is_mapped; > +} > + > +static bool __kvm_gmem_is_mapped(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + struct kvm_memslot_iter iter; > + > + lockdep_assert_held(&kvm->slots_lock); > + > + kvm_for_each_memslot_in_gfn_range(&iter, kvm_memslots(kvm), start, end) { > + struct kvm_memory_slot *memslot = iter.slot; > + gfn_t gfn_start, gfn_end, i; > + > + gfn_start = max(start, memslot->base_gfn); > + gfn_end = min(end, memslot->base_gfn + memslot->npages); > + if (WARN_ON_ONCE(gfn_start >= gfn_end)) > + continue; > + > + for (i = gfn_start; i < gfn_end; i++) { > + if (kvm_gmem_is_pfn_mapped(kvm, memslot, i)) > + return true; > + } > + } > + > + return false; > +} > + > +bool kvm_gmem_is_mapped(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + bool r; > + > + mutex_lock(&kvm->slots_lock); > + r = __kvm_gmem_is_mapped(kvm, start, end); > + mutex_unlock(&kvm->slots_lock); > + > + return r; > +} > + > +static int kvm_gmem_toggle_mappable(struct kvm *kvm, gfn_t start, gfn_t end, > + bool is_mappable) > +{ > + struct kvm_memslot_iter iter; > + int r = 0; > + > + mutex_lock(&kvm->slots_lock); > + > + kvm_for_each_memslot_in_gfn_range(&iter, kvm_memslots(kvm), start, end) { > + struct kvm_memory_slot *memslot = iter.slot; > + gfn_t gfn_start, gfn_end; > + > + gfn_start = max(start, memslot->base_gfn); > + gfn_end = min(end, memslot->base_gfn + memslot->npages); > + if (WARN_ON_ONCE(start >= end)) > + continue; > + > + if (is_mappable) > + r = kvm_slot_gmem_set_mappable(memslot, gfn_start, gfn_end); > + else > + r = kvm_slot_gmem_clear_mappable(memslot, gfn_start, gfn_end); > + > + if (WARN_ON_ONCE(r)) > + break; > + } > + > + mutex_unlock(&kvm->slots_lock); > + > + return r; > +} > + > +int kvm_gmem_set_mappable(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + return kvm_gmem_toggle_mappable(kvm, start, end, true); > +} > + > +int kvm_gmem_clear_mappable(struct kvm *kvm, gfn_t start, gfn_t end) > +{ > + return kvm_gmem_toggle_mappable(kvm, start, end, false); > +} > + > +#endif /* CONFIG_KVM_GMEM_MAPPABLE */ > + > /* Copy @len bytes from guest memory at '(@gfn * PAGE_SIZE) + @offset' to @data */ > static int __kvm_read_guest_page(struct kvm_memory_slot *slot, gfn_t gfn, > void *data, int offset, int len) > -- > 2.47.0.rc0.187.ge670bccf7e-goog >
