linux-kernel - [PATCH v12 12/12] KVM: guest_memfd: Add gmem_inode.flags field instead of using i

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Message-ID: <20251007221420.344669-13-seanjc@google.com>
Date: Tue,  7 Oct 2025 15:14:20 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>, 
	Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	David Hildenbrand <david@...hat.com>, Fuad Tabba <tabba@...gle.com>, 
	Ackerley Tng <ackerleytng@...gle.com>, Shivank Garg <shivankg@....com>, 
	Ashish Kalra <ashish.kalra@....com>, Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH v12 12/12] KVM: guest_memfd: Add gmem_inode.flags field
 instead of using i_private

Track a guest_memfd instance's flags in gmem_inode instead of burying them
in i_private.  Burning an extra 8 bytes per inode is well worth the added
clarity provided by explicit tracking.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 virt/kvm/guest_memfd.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 95267c92983b..10df35a9ffd4 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -30,6 +30,8 @@ struct gmem_file {
 struct gmem_inode {
 	struct shared_policy policy;
 	struct inode vfs_inode;
+
+	u64 flags;
 };
 
 static __always_inline struct gmem_inode *GMEM_I(struct inode *inode)
@@ -162,7 +164,7 @@ static struct folio *kvm_gmem_get_folio(struct inode *inode, pgoff_t index)
 
 static enum kvm_gfn_range_filter kvm_gmem_get_invalidate_filter(struct inode *inode)
 {
-	if ((u64)inode->i_private & GUEST_MEMFD_FLAG_INIT_SHARED)
+	if (GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED)
 		return KVM_FILTER_SHARED;
 
 	return KVM_FILTER_PRIVATE;
@@ -398,9 +400,7 @@ static pgoff_t kvm_gmem_get_index(struct kvm_memory_slot *slot, gfn_t gfn)
 
 static bool kvm_gmem_supports_mmap(struct inode *inode)
 {
-	const u64 flags = (u64)inode->i_private;
-
-	return flags & GUEST_MEMFD_FLAG_MMAP;
+	return GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_MMAP;
 }
 
 static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)
@@ -412,7 +412,7 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf)
 	if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
 		return VM_FAULT_SIGBUS;
 
-	if (!((u64)inode->i_private & GUEST_MEMFD_FLAG_INIT_SHARED))
+	if (!(GMEM_I(inode)->flags & GUEST_MEMFD_FLAG_INIT_SHARED))
 		return VM_FAULT_SIGBUS;
 
 	folio = kvm_gmem_get_folio(inode, vmf->pgoff);
@@ -601,7 +601,6 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 		goto err_fops;
 	}
 
-	inode->i_private = (void *)(unsigned long)flags;
 	inode->i_op = &kvm_gmem_iops;
 	inode->i_mapping->a_ops = &kvm_gmem_aops;
 	inode->i_mode |= S_IFREG;
@@ -611,6 +610,8 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
 	/* Unmovable mappings are supposed to be marked unevictable as well. */
 	WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
 
+	GMEM_I(inode)->flags = flags;
+
 	file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops);
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);
@@ -931,6 +932,8 @@ static struct inode *kvm_gmem_alloc_inode(struct super_block *sb)
 		return NULL;
 
 	mpol_shared_policy_init(&gi->policy, NULL);
+
+	gi->flags = 0;
 	return &gi->vfs_inode;
 }
 
-- 
2.51.0.710.ga91ca5db03-goog