On Mon, Mar 28, 2022 at 09:56:33PM +0000, Sean Christopherson wrote:

On Thu, Mar 10, 2022, Chao Peng wrote:

quoted

Extend the memslot definition to provide fd-based private memory support
by adding two new fields (private_fd/private_offset). The memslot then
can maintain memory for both shared pages and private pages in a single
memslot. Shared pages are provided by existing userspace_addr(hva) field
and private pages are provided through the new private_fd/private_offset
fields.

Since there is no 'hva' concept anymore for private memory so we cannot
rely on get_user_pages() to get a pfn, instead we use the newly added
memfile_notifier to complete the same job.

This new extension is indicated by a new flag KVM_MEM_PRIVATE.

Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>
---
 Documentation/virt/kvm/api.rst | 37 +++++++++++++++++++++++++++-------
 include/linux/kvm_host.h       |  7 +++++++
 include/uapi/linux/kvm.h       |  8 ++++++++
 3 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 3acbf4d263a5..f76ac598606c 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst

@@ -1307,7 +1307,7 @@ yet and must be cleared on entry.
 :Capability: KVM_CAP_USER_MEMORY
 :Architectures: all
 :Type: vm ioctl
-:Parameters: struct kvm_userspace_memory_region (in)
+:Parameters: struct kvm_userspace_memory_region(_ext) (in)
 :Returns: 0 on success, -1 on error
 
 ::

@@ -1320,9 +1320,17 @@ yet and must be cleared on entry.
 	__u64 userspace_addr; /* start of the userspace allocated memory */
   };
 
+  struct kvm_userspace_memory_region_ext {
+	struct kvm_userspace_memory_region region;

Peeking ahead, the partial switch to the _ext variant is rather gross.  I would
prefer that KVM use an entirely different, but binary compatible, struct internally.
And once the kernel supports C11[*], I'm pretty sure we can make the "region" in
_ext an anonymous struct, and make KVM's internal struct a #define of _ext.  That
should minimize the churn (no need to get the embedded "region" field), reduce
line lengths, and avoid confusion due to some flows taking the _ext but others
dealing with only the "base" struct.

Will try that.

Maybe kvm_user_memory_region or kvm_user_mem_region?  Though it's tempting to be
evil and usurp the old kvm_memory_region :-)

E.g. pre-C11 do

struct kvm_userspace_memory_region_ext {
	struct kvm_userspace_memory_region region;
	__u64 private_offset;
	__u32 private_fd;
	__u32 padding[5];
};

#ifdef __KERNEL__
struct kvm_user_mem_region {
	__u32 slot;
	__u32 flags;
	__u64 guest_phys_addr;
	__u64 memory_size; /* bytes */
	__u64 userspace_addr; /* start of the userspace allocated memory */
	__u64 private_offset;
	__u32 private_fd;
	__u32 padding[5];
};
#endif

and then post-C11 do

struct kvm_userspace_memory_region_ext {
#ifdef __KERNEL__

Is this #ifndef? As I think anonymous struct is only for kernel?

Thanks,
Chao

	struct kvm_userspace_memory_region region;
#else
	struct kvm_userspace_memory_region;
#endif
	__u64 private_offset;
	__u32 private_fd;
	__u32 padding[5];
};

#ifdef __KERNEL__
#define kvm_user_mem_region kvm_userspace_memory_region_ext
#endif

[*] https://lore.kernel.org/all/20220301145233.3689119-1-arnd@kernel.org (local)

quoted

+	__u64 private_offset;
+	__u32 private_fd;
+	__u32 padding[5];
+};