[tip: x86/core] x86/cpu/intel: Fix the MOVSL alignment preference for extended Families

[tip-bot2 for Sohil Mehta]

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

Commit-ID:     7e67f3617228318da655dc87bc705f9c5f7bb101
Gitweb:        https://git.kernel.org/tip/7e67f3617228318da655dc87bc705f9c5f7bb101
Author:        Sohil Mehta <sohil.mehta@xxxxxxxxx>
AuthorDate:    Wed, 19 Feb 2025 18:41:20 
Committer:     Ingo Molnar <mingo@xxxxxxxxxx>
CommitterDate: Wed, 19 Mar 2025 11:19:31 +01:00

x86/cpu/intel: Fix the MOVSL alignment preference for extended Families

The alignment preference for 32-bit MOVSL based bulk memory move has
been 8-byte for a long time. However this preference is only set for
Family 6 and 15 processors.

Use the same preference for upcoming Family numbers 18 and 19. Also, use
a simpler VFM based check instead of switching based on Family numbers.
Refresh the comment to reflect the new check.

Signed-off-by: Sohil Mehta <sohil.mehta@xxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Acked-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20250219184133.816753-3-sohil.mehta@xxxxxxxxx
---
 arch/x86/kernel/cpu/intel.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 291c828..99b4c40 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -440,23 +440,16 @@ static void intel_workarounds(struct cpuinfo_x86 *c)
 	    (c->x86_stepping < 0x6 || c->x86_stepping == 0xb))
 		set_cpu_bug(c, X86_BUG_11AP);
 
-
 #ifdef CONFIG_X86_INTEL_USERCOPY
 	/*
-	 * Set up the preferred alignment for movsl bulk memory moves
+	 * MOVSL bulk memory moves can be slow when source and dest are not
+	 * both 8-byte aligned. PII/PIII only like MOVSL with 8-byte alignment.
+	 *
+	 * Set the preferred alignment for Pentium Pro and newer processors, as
+	 * it has only been tested on these.
 	 */
-	switch (c->x86) {
-	case 4:		/* 486: untested */
-		break;
-	case 5:		/* Old Pentia: untested */
-		break;
-	case 6:		/* PII/PIII only like movsl with 8-byte alignment */
+	if (c->x86_vfm >= INTEL_PENTIUM_PRO)
 		movsl_mask.mask = 7;
-		break;
-	case 15:	/* P4 is OK down to 8-byte alignment */
-		movsl_mask.mask = 7;
-		break;
-	}
 #endif
 
 	intel_smp_check(c);