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* [PATCH] x86: clear incorrectly forced X86_FEATURE_LAHF_LM flag
@ 2009-08-08 11:53 Kevin Winchester
  2009-08-08 15:20 ` Borislav Petkov
  0 siblings, 1 reply; 80+ messages in thread
From: Kevin Winchester @ 2009-08-08 11:53 UTC (permalink / raw)
  To: Ingo Molnar, H. Peter Anvin, Thomas Gleixner
  Cc: Yinghai Lu, Andreas Herrmann, LKML

Due to an erratum with certain AMD Athlon 64 processors, the BIOS may
need to force enable the LAHF_LM capability.  Unfortunately, in at
least one case, the BIOS does this even for processors that do not
support the functionality.

Add a specific check that will clear the feature bit for processors
known not to support the LAHF/SAHF instructions.

Signed-off-by: Kevin Winchester <kjwinchester@gmail.com>
---

While making this change, I noticed the clause above my code:

    if((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)

It does not seem concerned with the possibility that some of the
upper 16 bits of level will be non-zero.  Is this intentional, or
should the upper 16 bits be masked off before the comparisons?

 arch/x86/kernel/cpu/amd.c |    8 ++++++++
 1 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index e2485b0..a2f0fe4 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -400,6 +400,14 @@ static void __cpuinit init_amd(struct cpuinfo_x86 *c)
 		level = cpuid_eax(1);
 		if((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
 			set_cpu_cap(c, X86_FEATURE_REP_GOOD);
+
+		/*
+		 * Some BIOSes incorrectly set this feature, but only
+		 * Revision E (with Extended Model = 2) actually supports
+		 * it.
+		 */
+		if (!(level & 0x00020000))
+			clear_cpu_cap(c, X86_FEATURE_LAHF_LM);
 	}
 	if (c->x86 == 0x10 || c->x86 == 0x11)
 		set_cpu_cap(c, X86_FEATURE_REP_GOOD);
-- 
1.6.4



^ permalink raw reply related	[flat|nested] 80+ messages in thread

end of thread, other threads:[~2009-09-06  4:42 UTC | newest]

Thread overview: 80+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2009-08-08 11:53 [PATCH] x86: clear incorrectly forced X86_FEATURE_LAHF_LM flag Kevin Winchester
2009-08-08 15:20 ` Borislav Petkov
2009-08-08 15:42   ` Ingo Molnar
2009-08-08 16:15   ` Ingo Molnar
2009-08-08 22:06   ` Kevin Winchester
2009-08-08 23:17   ` [PATCH v2] " Kevin Winchester
2009-08-10 13:12     ` Borislav Petkov
2009-08-10 22:56       ` [PATCH v3] " Kevin Winchester
2009-08-11  9:44         ` Borislav Petkov
2009-08-11 11:36         ` [tip:x86/urgent] x86: Clear " tip-bot for Kevin Winchester
2009-08-11 14:37         ` [PATCH v3] x86: clear " Mikael Pettersson
2009-08-11 14:56           ` Kevin Winchester
2009-08-11 15:51           ` Borislav Petkov
2009-08-11 15:55             ` Kevin Winchester
2009-08-11 16:01               ` Borislav Petkov
2009-08-12  0:15                 ` Kevin Winchester
2009-08-12 11:40                   ` Borislav Petkov
2009-08-12 23:02                     ` Kevin Winchester
2009-08-13 12:23                       ` Borislav Petkov
2009-08-13 12:31                         ` [PATCH 1/2] x86, msr: Add an AMD wrmsr with exception handling Borislav Petkov
2009-08-13 12:31                         ` [PATCH 2/2] x86: Clear incorrectly forced X86_FEATURE_LAHF_LM flag Borislav Petkov
2009-08-13 14:21                           ` Brian Gerst
2009-08-13 14:54                             ` Kevin Winchester
2009-08-13 15:55                               ` Brian Gerst
2009-08-13 16:18                                 ` Borislav Petkov
2009-08-13 22:45                                 ` Kevin Winchester
2009-08-13 15:54                             ` Borislav Petkov
2009-08-13 14:57                         ` [PATCH v3] x86: clear " Kevin Winchester
2009-08-13 23:24                         ` Kevin Winchester
2009-08-14 12:00                           ` Borislav Petkov
2009-08-14 12:06                             ` [PATCH 1/2] x86, msr: Add a AMD wrmsr with exception handling Borislav Petkov
2009-08-15 17:06                               ` [tip:x86/urgent] " tip-bot for Borislav Petkov
2009-08-14 12:06                             ` [PATCH 2/2] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-15 17:06                               ` [tip:x86/urgent] " tip-bot for Borislav Petkov
2009-08-16  6:41                                 ` Ingo Molnar
2009-08-16 20:10                                   ` Kevin Winchester
2009-08-16 20:51                                     ` Ingo Molnar
2009-08-16 21:49                                   ` Borislav Petkov
2009-08-21 17:40                                     ` H. Peter Anvin
2009-08-22 16:37                                       ` Borislav Petkov
2009-08-24 20:34                                         ` H. Peter Anvin
2009-08-25  5:52                                           ` Borislav Petkov
2009-08-25  6:44                                             ` H. Peter Anvin
2009-08-30 11:43                                               ` Borislav Petkov
2009-08-30 11:50                                                 ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Borislav Petkov
2009-08-30 11:50                                                 ` [PATCH 2/3] x86, msr: rewrite AMD rd/wrmsr variants Borislav Petkov
2009-08-30 20:03                                                   ` H. Peter Anvin
2009-08-30 20:46                                                     ` Borislav Petkov
2009-08-30 20:04                                                   ` H. Peter Anvin
2009-08-30 11:50                                                 ` [PATCH 3/3] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-30 19:22                                                   ` H. Peter Anvin
2009-08-30 19:30                                                     ` Borislav Petkov
2009-08-30 20:02                                                       ` H. Peter Anvin
2009-08-30 20:29                                                         ` Borislav Petkov
2009-08-30 20:48                                                           ` H. Peter Anvin
2009-08-31  7:34                                                             ` Borislav Petkov
2009-08-31  7:50                                                               ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Borislav Petkov
2009-08-31 23:37                                                                 ` [tip:x86/cpu] x86, msr: Add " tip-bot for Borislav Petkov
2009-09-01 11:05                                                                   ` Ingo Molnar
2009-09-01 13:06                                                                     ` Borislav Petkov
2009-09-04 14:08                                                                   ` Ingo Molnar
2009-09-04 16:26                                                                     ` H. Peter Anvin
2009-09-04 17:06                                                                     ` [tip:x86/cpu] x86, msr: change msr-reg.o to obj-y, and export its symbols tip-bot for H. Peter Anvin
2009-09-05  9:57                                                                       ` Borislav Petkov
2009-09-06  4:41                                                                         ` H. Peter Anvin
2009-08-31 23:38                                                                 ` [tip:x86/cpu] x86, msr: CFI annotations, cleanups for msr-reg.S tip-bot for H. Peter Anvin
2009-09-03 22:55                                                                 ` [PATCH 1/3] x86, msr: add rd/wrmsr interfaces with preset registers Andrew Morton
2009-09-03 22:57                                                                   ` H. Peter Anvin
2009-09-03 23:14                                                                     ` Andrew Morton
2009-09-03 23:22                                                                       ` H. Peter Anvin
2009-09-04  6:39                                                                       ` Ingo Molnar
2009-09-04  8:27                                                                         ` Borislav Petkov
2009-08-31  7:50                                                               ` [PATCH 2/3] x86, msr: rewrite AMD rd/wrmsr variants Borislav Petkov
2009-08-31 23:37                                                                 ` [tip:x86/cpu] x86, msr: Rewrite " tip-bot for Borislav Petkov
2009-08-31  7:50                                                               ` [PATCH 3/3] x86, AMD: Disable wrongly set X86_FEATURE_LAHF_LM CPUID bit Borislav Petkov
2009-08-31 23:37                                                                 ` [tip:x86/cpu] " tip-bot for Borislav Petkov
2009-08-31  8:14                                                             ` [PATCH 3/3] " Borislav Petkov
2009-08-31 18:03                                                               ` H. Peter Anvin
2009-08-30 17:07                                                 ` [tip:x86/urgent] " H. Peter Anvin
2009-08-30 19:17                                                   ` Borislav Petkov

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