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

    ae6012d72fa6 ("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>
Cc: Aruna Ramakrishna <aruna.ramakrishna@oracle.com>
Cc: Tony W Wang-oc <TonyWWang-oc@zhaoxin.com>
---
Changes from the last posting:
https://lore.kernel.org/lkml/20250214010607.7067-3-chang.seok.bae@intel.com/
* Massage the changelog

Additional Context:
  Previously, the concern was raised about environments where XGETBV1 is
  unavailable — such as in some virtual machines:

    https://lore.kernel.org/lkml/20250102075419.2559-1-TonyWWang-oc@zhaoxin.com

  That patch tried to sidestep the problem by skipping PKRU updates
  entirely when XGETBV1 is inaccessible. However, this assumed the
  dependency was necessary, which isn’t the case.
---
 arch/x86/kernel/fpu/xstate.h | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index aadf02aed071..a6d987c16293 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/arch/x86/kernel/fpu/xstate.h
@@ -84,18 +84,15 @@ 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;
 
@@ -319,7 +316,7 @@ 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;
 }
-- 
2.45.2

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     d1e420772cd1eb0afe5858619c73ce36f3e781a1
Gitweb:        https://git.kernel.org/tip/d1e420772cd1eb0afe5858619c73ce36f3e781a1
Author:        Chang S. Bae <chang.seok.bae@intel.com>
AuthorDate:    Tue, 15 Apr 2025 19:16:58 -07:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 16 Apr 2025 10:01:03 +02:00

x86/pkeys: Simplify PKRU update in signal frame

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

    ae6012d72fa6 ("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
---
 arch/x86/kernel/fpu/xstate.h |  9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.h b/arch/x86/kernel/fpu/xstate.h
index 4231e44..a0256ef 100644
--- a/arch/x86/kernel/fpu/xstate.h
+++ b/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;
 }