From: Sean Christopherson Implement kvm_gmem_get_memory_attributes() for guest_memfd to allow the KVM core and architecture code to query per-GFN memory attributes. kvm_gmem_get_memory_attributes() finds the memory slot for a given GFN and queries the guest_memfd file's to determine if the page is marked as private. If vm_memory_attributes is not enabled, there is no shared/private tracking at the VM level. Install the guest_memfd implementation as long as guest_memfd is enabled to give guest_memfd a chance to respond on attributes. guest_memfd should look up attributes regardless of whether this memslot is gmem-only since attributes are now tracked by gmem regardless of whether mmap() is enabled. Signed-off-by: Sean Christopherson Co-developed-by: Ackerley Tng Signed-off-by: Ackerley Tng --- include/linux/kvm_host.h | 2 ++ virt/kvm/guest_memfd.c | 37 +++++++++++++++++++++++++++++++++++++ virt/kvm/kvm_main.c | 3 +++ 3 files changed, 42 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 0e7920a0f957..c12ee89392d8 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2544,6 +2544,8 @@ bool kvm_arch_post_set_memory_attributes(struct kvm *kvm, struct kvm_gfn_range *range); #endif /* CONFIG_KVM_VM_MEMORY_ATTRIBUTES */ +unsigned long kvm_gmem_get_memory_attributes(struct kvm *kvm, gfn_t gfn); + #ifdef CONFIG_KVM_GUEST_MEMFD int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, gfn_t gfn, kvm_pfn_t *pfn, struct page **page, diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c index 7a970e5fab67..810fec394075 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -515,6 +515,43 @@ static int kvm_gmem_mmap(struct file *file, struct vm_area_struct *vma) return 0; } +unsigned long kvm_gmem_get_memory_attributes(struct kvm *kvm, gfn_t gfn) +{ + struct kvm_memory_slot *slot = gfn_to_memslot(kvm, gfn); + struct inode *inode; + unsigned long attrs; + + /* + * If this gfn has no associated memslot, there's no chance of the gfn + * being backed by private memory, since guest_memfd must be used for + * private memory, and guest_memfd must be associated with some memslot. + */ + if (!slot) + return 0; + + CLASS(gmem_get_file, file)(slot); + if (!file) + return 0; + + inode = file_inode(file); + + /* + * Acquire the filemap lock to ensure the mtree lookup gets a + * stable result. The caller _must_ still protect consumption + * of private vs. shared by checking + * mmu_invalidate_retry_gfn() under mmu_lock to serialize + * against ongoing attribute updates. Acquiring the filemap + * lock only ensures a stable _lookup_, the result can become + * stale as soon as the lock is dropped. + */ + filemap_invalidate_lock_shared(inode->i_mapping); + attrs = kvm_gmem_get_attributes(inode, kvm_gmem_get_index(slot, gfn)); + filemap_invalidate_unlock_shared(inode->i_mapping); + + return attrs; +} +EXPORT_SYMBOL_GPL(kvm_gmem_get_memory_attributes); + static struct file_operations kvm_gmem_fops = { .mmap = kvm_gmem_mmap, .open = generic_file_open, diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 4dc9fd941ecb..5d06e2c74ae7 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2676,6 +2676,9 @@ static void kvm_init_memory_attributes(void) if (vm_memory_attributes) static_call_update(__kvm_get_memory_attributes, kvm_get_vm_memory_attributes); + else if (IS_ENABLED(CONFIG_KVM_GUEST_MEMFD)) + static_call_update(__kvm_get_memory_attributes, + kvm_gmem_get_memory_attributes); else static_call_update(__kvm_get_memory_attributes, (void *)__static_call_return0); -- 2.53.0.rc1.225.gd81095ad13-goog