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

Commit-ID:     1ae899e413105aa81068d0282ab6e22974891d74
Gitweb:        https://git.kernel.org/tip/1ae899e413105aa81068d0282ab6e22974891d74
Author:        Uros Bizjak <ubizjak@gmail.com>
AuthorDate:    Wed, 02 Apr 2025 20:08:05 +02:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Wed, 02 Apr 2025 22:26:17 +02:00

x86/idle: Standardize argument types for MONITOR{,X} and MWAIT{,X} instruction wrappers on 'u32'

MONITOR and MONITORX expect 32-bit unsigned integer arguments in the %ecx
and %edx registers. MWAIT and MWAITX expect 32-bit usigned int
argument in %eax and %ecx registers.

Some of the helpers around these instructions in <asm/mwait.h> are using
too wide types (long), standardize on u32 instead that makes it clear that
this is a hardware ABI.

[ mingo: Cleaned up the changelog. ]

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250402180827.3762-1-ubizjak@gmail.com
---
 arch/x86/include/asm/mwait.h | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/arch/x86/include/asm/mwait.h b/arch/x86/include/asm/mwait.h
index 54dc313..3377869 100644
--- a/arch/x86/include/asm/mwait.h
+++ b/arch/x86/include/asm/mwait.h
@@ -25,23 +25,21 @@
 #define TPAUSE_C01_STATE		1
 #define TPAUSE_C02_STATE		0
 
-static __always_inline void __monitor(const void *eax, unsigned long ecx,
-			     unsigned long edx)
+static __always_inline void __monitor(const void *eax, u32 ecx, u32 edx)
 {
 	/* "monitor %eax, %ecx, %edx;" */
 	asm volatile(".byte 0x0f, 0x01, 0xc8;"
 		     :: "a" (eax), "c" (ecx), "d"(edx));
 }
 
-static __always_inline void __monitorx(const void *eax, unsigned long ecx,
-			      unsigned long edx)
+static __always_inline void __monitorx(const void *eax, u32 ecx, u32 edx)
 {
 	/* "monitorx %eax, %ecx, %edx;" */
 	asm volatile(".byte 0x0f, 0x01, 0xfa;"
 		     :: "a" (eax), "c" (ecx), "d"(edx));
 }
 
-static __always_inline void __mwait(unsigned long eax, unsigned long ecx)
+static __always_inline void __mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
 
@@ -76,8 +74,7 @@ static __always_inline void __mwait(unsigned long eax, unsigned long ecx)
  * EAX                     (logical) address to monitor
  * ECX                     #GP if not zero
  */
-static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx,
-				     unsigned long ecx)
+static __always_inline void __mwaitx(u32 eax, u32 ebx, u32 ecx)
 {
 	/* No MDS buffer clear as this is AMD/HYGON only */
 
@@ -95,7 +92,7 @@ static __always_inline void __mwaitx(unsigned long eax, unsigned long ebx,
  * executing mwait, it would otherwise go unnoticed and the next tick
  * would not be reprogrammed accordingly before mwait ever wakes up.
  */
-static __always_inline void __sti_mwait(unsigned long eax, unsigned long ecx)
+static __always_inline void __sti_mwait(u32 eax, u32 ecx)
 {
 	mds_idle_clear_cpu_buffers();
 	/* "mwait %eax, %ecx;" */

On 02/04/2025 9:43 pm, tip-bot2 for Uros Bizjak wrote:
> The following commit has been merged into the x86/mm branch of tip:
>
> Commit-ID:     1ae899e413105aa81068d0282ab6e22974891d74
> Gitweb:        https://git.kernel.org/tip/1ae899e413105aa81068d0282ab6e22974891d74
> Author:        Uros Bizjak <ubizjak@gmail.com>
> AuthorDate:    Wed, 02 Apr 2025 20:08:05 +02:00
> Committer:     Ingo Molnar <mingo@kernel.org>
> CommitterDate: Wed, 02 Apr 2025 22:26:17 +02:00
>
> x86/idle: Standardize argument types for MONITOR{,X} and MWAIT{,X} instruction wrappers on 'u32'
>
> MONITOR and MONITORX expect 32-bit unsigned integer arguments in the %ecx
> and %edx registers. MWAIT and MWAITX expect 32-bit usigned int
> argument in %eax and %ecx registers.
>
> Some of the helpers around these instructions in <asm/mwait.h> are using
> too wide types (long), standardize on u32 instead that makes it clear that
> this is a hardware ABI.
>
> [ mingo: Cleaned up the changelog. ]
>
> Signed-off-by: Uros Bizjak <ubizjak@gmail.com>

Something I noticed while looking over this is that you want to push the
u32's up into the callers too.

mwait_idle_with_hints() with have (marginally) better code gen by
swapping it's unsigned longs for u32's.

~Andrew