From: Sean Christopherson <[email protected]> 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 <[email protected]> Co-developed-by: Ackerley Tng <[email protected]> Signed-off-by: Ackerley Tng <[email protected]> --- include/linux/kvm_host.h | 2 ++ virt/kvm/guest_memfd.c | 29 +++++++++++++++++++++++++++++ virt/kvm/kvm_main.c | 3 +++ 3 files changed, 34 insertions(+) diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index 512febf47c265..b8418cc5851f1 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2543,6 +2543,8 @@ 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 26cec833766c3..f62facc3ab776 100644 --- a/virt/kvm/guest_memfd.c +++ b/virt/kvm/guest_memfd.c @@ -518,6 +518,35 @@ 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); + + /* + * 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 false; + + /* + * Don't take the filemap invalidation lock, as temporarily acquiring + * that lock wouldn't provide any meaningful protection. The caller + * _must_ protect consumption of private vs. shared by checking + * mmu_invalidate_retry_gfn() under mmu_lock. + */ + guard(rcu)(); + + return kvm_gmem_get_attributes(file_inode(file), + kvm_gmem_get_index(slot, gfn)); +} +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 6c29770dfa7c8..c73ebdb73070e 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -2660,6 +2660,9 @@ 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); -- 2.51.0.858.gf9c4a03a3a-goog
