On 5/27/2025 4:25 PM, Binbin Wu wrote:
On 5/15/2025 7:41 AM, Ackerley Tng wrote:
Track guest_memfd memory's shareability status within the inode as
opposed to the file, since it is property of the guest_memfd's memory
contents.
Shareability is a property of the memory and is indexed using the
page's index in the inode. Because shareability is the memory's
property, it is stored within guest_memfd instead of within KVM, like
in kvm->mem_attr_array.
KVM_MEMORY_ATTRIBUTE_PRIVATE in kvm->mem_attr_array must still be
retained to allow VMs to only use guest_memfd for private memory and
some other memory for shared memory.
Not all use cases require guest_memfd() to be shared with the host
when first created. Add a new flag, GUEST_MEMFD_FLAG_INIT_PRIVATE,
which when set on KVM_CREATE_GUEST_MEMFD, initializes the memory as
private to the guest, and therefore not mappable by the
host. Otherwise, memory is shared until explicitly converted to
private.
Signed-off-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>
Co-developed-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
Signed-off-by: Vishal Annapurve <vannapurve@xxxxxxxxxx>
Co-developed-by: Fuad Tabba <tabba@xxxxxxxxxx>
Signed-off-by: Fuad Tabba <tabba@xxxxxxxxxx>
Change-Id: If03609cbab3ad1564685c85bdba6dcbb6b240c0f
---
Documentation/virt/kvm/api.rst | 5 ++
include/uapi/linux/kvm.h | 2 +
virt/kvm/guest_memfd.c | 124 ++++++++++++++++++++++++++++++++-
3 files changed, 129 insertions(+), 2 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 86f74ce7f12a..f609337ae1c2 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6408,6 +6408,11 @@ belonging to the slot via its userspace_addr.
The use of GUEST_MEMFD_FLAG_SUPPORT_SHARED will not be allowed for CoCo VMs.
This is validated when the guest_memfd instance is bound to the VM.
+If the capability KVM_CAP_GMEM_CONVERSIONS is supported, then the 'flags' field
+supports GUEST_MEMFD_FLAG_INIT_PRIVATE.
It seems that the sentence is stale?
Didn't find the definition of KVM_CAP_GMEM_CONVERSIONS.
Aha! It's a typo, should be KVM_CAP_GMEM_CONVERSION.
Setting GUEST_MEMFD_FLAG_INIT_PRIVATE
+will initialize the memory for the guest_memfd as guest-only and not faultable
+by the host.
+
[...]
static int kvm_gmem_init_fs_context(struct fs_context *fc)
@@ -549,12 +645,26 @@ static const struct inode_operations kvm_gmem_iops = {
static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
loff_t size, u64 flags)
{
+ struct kvm_gmem_inode_private *private;
struct inode *inode;
+ int err;
inode = alloc_anon_secure_inode(kvm_gmem_mnt->mnt_sb, name);
if (IS_ERR(inode))
return inode;
+ err = -ENOMEM;
+ private = kzalloc(sizeof(*private), GFP_KERNEL);
+ if (!private)
+ goto out;
+
+ mt_init(&private->shareability);
shareability is defined only when CONFIG_KVM_GMEM_SHARED_MEM enabled, should be done within CONFIG_KVM_GMEM_SHARED_MEM .
+ inode->i_mapping->i_private_data = private;
+
+ err = kvm_gmem_shareability_setup(private, size, flags);
+ if (err)
+ goto out;
+
inode->i_private = (void *)(unsigned long)flags;
inode->i_op = &kvm_gmem_iops;
inode->i_mapping->a_ops = &kvm_gmem_aops;
@@ -566,6 +676,11 @@ static struct inode *kvm_gmem_inode_make_secure_inode(const char *name,
WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping));
return inode;
+
+out:
+ iput(inode);
+
+ return ERR_PTR(err);
}
[...]
