fix(vmm): Support kernel >= 5.16 and < 5.17 for xfeature enabling

The Linux kernel introduced some arch_prctl() APIs (ARCH_GET_XCOMP_SUPP,
ARCH_GET_XCOMP_PERM and ARCH_REQ_XCOMP_PERM) to support dynamic XSTATE
feature enabling for "userspace applications" in 5.16 [1]. To support
that for "KVM guest", v5.17 introduced additional arch_prctl() APIs
(ARCH_GET_XCOMP_GUEST_PERM and ARCH_REQ_XCOMP_GUEST_PERM) [2]. Note that
ARCH_XCOMP_GUEST_SUPP does not exist, so regardless of userspace
application or KVM guest, ARCH_GET_XCOMP_SUPP is used to retrieve
supported features. As a result, kernel versions >= 5.16 and < 5.17
report supported features via ARCH_GET_XCOMP_SUPP but
ARCH_REQ_XCOMP_GUEST_PERM fail with EINVAL.

[1]: torvalds/linux@db8268d
[2]: torvalds/linux@980fe2f
Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

src/vmm/src/arch/x86_64/xstate.rs

@@ -86,14 +86,23 @@ fn get_supported_xfeatures() -> Result<Option<u64>, std::io::Error> {
 fn request_xfeature_permission(xfeature: u32) -> Result<(), std::io::Error> {
     // SAFETY: Safe because the third input (`addr`) is a valid `c_ulong` value.
     // https://man7.org/linux/man-pages/man2/arch_prctl.2.html
-    SyscallReturnCode(unsafe {
+    match SyscallReturnCode(unsafe {
         libc::syscall(
             libc::SYS_arch_prctl,
             arch_prctl::ARCH_REQ_XCOMP_GUEST_PERM as libc::c_ulong,
             xfeature as libc::c_ulong,
         )
     })
     .into_empty_result()
+    {
+        Ok(()) => Ok(()),
+        // EINVAL is returned if the dynamic XSTATE feature enabling for "guest" is not supported
+        // although that for "userspace application" is supported (e.g. kernel versions >= 5.16 and
+        // < 5.17).
+        // https://github.com/torvalds/linux/commit/980fe2fddcff21937c93532b4597c8ea450346c1
+        Err(err) if err.raw_os_error() == Some(libc::EINVAL) => Ok(()),
+        Err(err) => Err(err),
+    }
 }
 
 #[cfg(test)]