On 18/10/25 07:11, Ackerley Tng wrote:
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);
I am trying to make it work with TEE-IO where fd of VFIO MMIO is a dmabuf fd
while the rest (guest RAM) is gmemfd. The above suggests that if there is
gmemfd - then the memory attributes are handled by gmemfd which is... expected?
The problem at hand is that kvm_mmu_faultin_pfn() fails at "if (fault->is_private !=
kvm_mem_is_private(kvm, fault->gfn))" and marking MMIO as private using
kvm_vm_ioctl_set_mem_attributes() does not work as kvm_gmem_get_memory_attributes() fails on
dmabuf fds.
I worked around this like below but wonder what is the proper way? Thanks,
@@ -768,13 +768,13 @@ unsigned long kvm_gmem_get_memory_attributes(struct kvm
*kvm, gfn_t gfn)
*/
if (!slot)
return 0;
CLASS(gmem_get_file, file)(slot);
if (!file)
- return false;
+ return kvm_get_vm_memory_attributes(kvm, gfn);
/*
* 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.
--
Alexey
