diff mbox series

x86/lib/memmove: Decouple ERMS from FSRM

Message ID Y/yK0dyzI0MMdTie@zn.tnic
State New
Headers
Series x86/lib/memmove: Decouple ERMS from FSRM |

Commit Message

Borislav Petkov Feb. 27, 2023, 10:49 a.m. UTC 
  On Wed, Feb 08, 2023 at 06:10:50PM +0100, Peter Zijlstra wrote:
> Hi,
> 
> This version is fully tested and includes a few NOP twiddles inspired by the
> objtool patches I'll post separately.
> 
> Also available at:
> 
>   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git/log/?h=x86/core

Ontop of the first two:

From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Sun, 26 Feb 2023 21:04:26 +0100
Subject: [PATCH] x86/lib/memmove: Decouple ERMS from FSRM

Up until now it was perceived that FSRM is an improvement to ERMS and
thus it was made dependent on latter.

However, there are AMD BIOSes out there which allow for disabling of
either features and this preventing kernels from booting due to the CMP
disappearing and thus breaking the logic in the memmove() function.

Similar observation happens on some VM migration scenarios.

Patch the proper sequences depending on which feature is enabled.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reported-by: Daniel Verkamp <dverkamp@chromium.org>
Reported-by: Jiri Slaby <jirislaby@kernel.org>
---
 arch/x86/lib/memmove_64.S | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

Comments

Yahu Gao April 27, 2023, 9:22 a.m. UTC | #1 
Tested-by: Yahu Gao gaoyh12@lenove.com

Now [PATCH V3 2/4] has a conflict with commit
5d1dd961e74334a2178264193ea813d44ce5e725

Except the conflict it fixed the issue disabling ERMS in AMD BIOSes.
diff mbox series

Patch

diff --git a/arch/x86/lib/memmove_64.S b/arch/x86/lib/memmove_64.S
index 02661861e5dd..0559b206fb11 100644
--- a/arch/x86/lib/memmove_64.S
+++ b/arch/x86/lib/memmove_64.S
@@ -38,10 +38,12 @@  SYM_FUNC_START(__memmove)
 	cmp %rdi, %r8
 	jg 2f
 
-	/* FSRM implies ERMS => no length checks, do the copy directly */
+#define CHECK_LEN	cmp $0x20, %rdx; jb 1f
+#define MEMMOVE_BYTES	movq %rdx, %rcx; rep movsb; RET
 .Lmemmove_begin_forward:
-	ALTERNATIVE "cmp $0x20, %rdx; jb 1f", "", X86_FEATURE_FSRM
-	ALTERNATIVE "", "jmp .Lmemmove_erms", X86_FEATURE_ERMS
+	ALTERNATIVE_2 __stringify(CHECK_LEN), \
+		      __stringify(CHECK_LEN; MEMMOVE_BYTES), X86_FEATURE_ERMS, \
+		      __stringify(MEMMOVE_BYTES), X86_FEATURE_FSRM
 
 	/*
 	 * movsq instruction have many startup latency
@@ -207,11 +209,6 @@  SYM_FUNC_START(__memmove)
 	movb %r11b, (%rdi)
 13:
 	RET
-
-.Lmemmove_erms:
-	movq %rdx, %rcx
-	rep movsb
-	RET
 SYM_FUNC_END(__memmove)
 EXPORT_SYMBOL(__memmove)