On 7/29/2026 8:35 AM, Ackerley Tng via B4 Relay wrote:
From: Sean Christopherson<[email protected]>
Start plumbing in guest_memfd support for in-place private<=>shared
conversions by tracking attributes via a maple tree. KVM currently tracks
private vs. shared attributes on a per-VM basis, which made sense when a
guest_memfd_only_ supported private memory, but tracking per-VM simply
can't work for in-place conversions as the shared/private status of a given
page needs to be per-gmem_inode, not per-VM.
Use the filemap invalidation lock to protect the maple tree, as taking the
lock for read when faulting in memory (for userspace or the guest) isn't
expected to result in meaningful contention, and using a separate lock
would add significant complexity (avoiding deadlock is quite difficult).
Co-developed-by: Vishal Annapurve<[email protected]>
Signed-off-by: Vishal Annapurve<[email protected]>
Co-developed-by: Fuad Tabba<[email protected]>
Signed-off-by: Fuad Tabba<[email protected]>
Signed-off-by: Sean Christopherson<[email protected]>
Tested-by: Shivank Garg<[email protected]>
Co-developed-by: Ackerley Tng<[email protected]>
Signed-off-by: Ackerley Tng<[email protected]>
Reviewed-by: Xiaoyao Li <[email protected]>
<...>
static __always_inline struct gmem_inode *GMEM_I(struct inode *inode)
@@ -60,9 +68,25 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot
*slot, gfn_t gfn)
return gfn - slot->base_gfn + slot->gmem.pgoff;
}
+static u64 kvm_gmem_interpret_entry(struct inode *inode, void *entry)
Ummm, I'm not sure on the name. It doesn't look like KVM's style?
Maybe, just kvm_gmem_get_attributes()?
+{
+ if (WARN_ON_ONCE(!entry)) {
+ bool initially_shared = GMEM_I(inode)->flags &
+ GUEST_MEMFD_FLAG_INIT_SHARED;
+
+ return initially_shared ? 0 : KVM_MEMORY_ATTRIBUTE_PRIVATE;
+ }
+
+ return xa_to_value(entry);
+}
