x86/pkeys: Simplify PKRU update in signal frame

commit d1e4207 upstream.

The signal delivery logic was modified to always set the PKRU bit in
xregs_state->header->xfeatures by this commit:

    ae6012d ("x86/pkeys: Ensure updated PKRU value is XRSTOR'd")

However, the change derives the bitmask value using XGETBV(1), rather
than simply updating the buffer that already holds the value. Thus, this
approach induces an unnecessary dependency on XGETBV1 for PKRU handling.

Eliminate the dependency by using the established helper function.
Subsequently, remove the now-unused 'mask' argument.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20250416021720.12305-9-chang.seok.bae@intel.com
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ChangSeokBae

arch/x86/kernel/fpu/xstate.h

@@ -85,18 +85,15 @@ static inline int set_xfeature_in_sigframe(struct xregs_state __user *xbuf, u64
 /*
  * Update the value of PKRU register that was already pushed onto the signal frame.
  */
-static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u64 mask, u32 pkru)
+static inline int update_pkru_in_sigframe(struct xregs_state __user *buf, u32 pkru)
 {
-	u64 xstate_bv;
 	int err;
 
 	if (unlikely(!cpu_feature_enabled(X86_FEATURE_OSPKE)))
 		return 0;
 
 	/* Mark PKRU as in-use so that it is restored correctly. */
-	xstate_bv = (mask & xfeatures_in_use()) | XFEATURE_MASK_PKRU;
-
-	err =  __put_user(xstate_bv, &buf->header.xfeatures);
+	err = set_xfeature_in_sigframe(buf, XFEATURE_MASK_PKRU);
 	if (err)
 		return err;
 
@@ -320,7 +317,7 @@ static inline int xsave_to_user_sigframe(struct xregs_state __user *buf, u32 pkr
 	clac();
 
 	if (!err)
-		err = update_pkru_in_sigframe(buf, mask, pkru);
+		err = update_pkru_in_sigframe(buf, pkru);
 
 	return err;
 }