[PATCH RFC 3/3] KVM: guest_memfd: Enforce NUMA mempolicy if available

[Shivank Garg <shivankg@amd.com>]

From: Shivansh Dhiman <shivansh.dhiman@amd.com>

Enforce memory policy on guest-memfd to provide proper NUMA support.
Previously, guest-memfd allocations were following local NUMA node id in
absence of process mempolicy, resulting in random memory allocation.
Moreover, it cannot use mbind() since memory isn't mapped to userspace.

To support NUMA policies, retrieve the mempolicy struct from
i_private_data part of memfd's inode. Use filemap_grab_folio_mpol() to
ensure that allocations follow the specified memory policy.

Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
Signed-off-by: Shivank Garg <shivankg@amd.com>
---
 virt/kvm/guest_memfd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 8f1877be4976..8553d7069ba8 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -130,12 +130,15 @@ static struct folio *__kvm_gmem_get_folio(struct inode *inode, pgoff_t index,
 					  bool allow_huge)
 {
 	struct folio *folio = NULL;
+	struct mempolicy *mpol;
 
 	if (gmem_2m_enabled && allow_huge)
 		folio = kvm_gmem_get_huge_folio(inode, index, PMD_ORDER);
 
-	if (!folio)
-		folio = filemap_grab_folio(inode->i_mapping, index);
+	if (!folio) {
+		mpol = (struct mempolicy *)(inode->i_mapping->i_private_data);
+		folio = filemap_grab_folio_mpol(inode->i_mapping, index, mpol);
+	}
 
 	pr_debug("%s: allocate folio with PFN %lx order %d\n",
 		 __func__, folio_pfn(folio), folio_order(folio));
-- 
2.34.1