[RFC PATCH 28/39] KVM: guest_memfd: Use vm_type to determine default faultability

Ackerley Tng
2024-09-10T23:45:22Z

Memory of a KVM_X86_SW_PROTECTED_VM defaults to faultable to align
with the default in kvm->mem_attr_array.

For this RFC, determine default faultability when associating a range
with a memslot.

Another option is to determine default faultability at guest_memfd
creation time. guest_memfd is created for a specific VM, hence we can
set default faultability based on the VM type.

In future, if different struct kvms are bound to the same guest_memfd
inode, all the struct kvms must be of the same vm_type.

TODO: Perhaps faultability should be based on kvm->mem_attr_array?

Signed-off-by: Ackerley Tng <ackerleytng@google.com>

---
virt/kvm/guest_memfd.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index fc2483e35876..1d4dfe0660ad 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -1256,6 +1256,23 @@ static struct file *kvm_gmem_inode_create_getfile(void *priv, loff_t size,
return file;
}

+static void kvm_gmem_set_default_faultability_by_vm_type(struct inode *inode,
+ u8 vm_type,
+ loff_t start, loff_t end)
+{
+ bool faultable;
+
+ switch (vm_type) {
+ case KVM_X86_SW_PROTECTED_VM:
+ faultable = true;
+ break;
+ default:
+ faultable = false;
+ }
+
+ WARN_ON(kvm_gmem_set_faultable(inode, start, end, faultable));
+}
+
static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags)
{
struct kvm_gmem *gmem;
@@ -1378,6 +1395,11 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
slot->gmem.pgoff = start;

xa_store_range(&gmem->bindings, start, end - 1, slot, GFP_KERNEL);
+
+ kvm_gmem_set_default_faultability_by_vm_type(file_inode(file),
+ kvm->arch.vm_type,
+ start, end);
+
filemap_invalidate_unlock(inode->i_mapping);

/*
--
2.46.0.598.g6f2099f65c-goog