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.

Reviewed-by: Shivank Garg <shivankg@amd.com>
Tested-by: Shivank Garg <shivankg@amd.com>
Link: https://lore.kernel.org/r/20251016172853.52451-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 4463643bd0a29862ea6e2a1ffbfca2c2de554248..20f6e7fab58d9c1d431e338b4e4787fd7c090c98 100644 (file)
--- 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)
@@ -154,7 +156,7 @@ 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;
@@ -385,9 +387,7 @@ static inline struct file *kvm_gmem_get_file(struct kvm_memory_slot *slot)
 
 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)
@@ -399,7 +399,7 @@ 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);
@@ -588,7 +588,6 @@ 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;
@@ -598,6 +597,8 @@ 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);
@@ -917,6 +918,8 @@ 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;
 }