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From: Andi Kleen <andi@firstfloor.org>
To: x86@kernel.org
Cc: luto@amacapital.net, linux-kernel@vger.kernel.org,
	Andi Kleen <ak@linux.intel.com>
Subject: [PATCH 3/9] x86: Make old K8 swapgs workaround conditional
Date: Mon, 21 Mar 2016 09:16:03 -0700	[thread overview]
Message-ID: <1458576969-13309-4-git-send-email-andi@firstfloor.org> (raw)
In-Reply-To: <1458576969-13309-1-git-send-email-andi@firstfloor.org>

From: Andi Kleen <ak@linux.intel.com>

Every gs selector/index reload always paid an extra MFENCE
between the two SWAPGS. This was to work around an old
bug in early K8 steppings.  All other CPUs don't need the extra
mfence. Patch the extra MFENCE only in for K8.

v2: Use set_cpu_bug()
v3: Use ALTERNATIVE directly
Signed-off-by: Andi Kleen <ak@linux.intel.com>
---
 arch/x86/entry/entry_64.S          | 2 +-
 arch/x86/include/asm/cpufeatures.h | 1 +
 arch/x86/kernel/cpu/amd.c          | 3 +++
 3 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index c605710..252bce4 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -786,7 +786,7 @@ ENTRY(native_load_gs_index)
 	SWAPGS
 gs_change:
 	movl	%edi, %gs
-2:	mfence					/* workaround */
+2:	ALTERNATIVE "", "mfence", X86_BUG_SWAPGS_MFENCE
 	SWAPGS
 	popfq
 	ret
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 074b760..f3b3ff8 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -288,6 +288,7 @@
 #define X86_BUG_FXSAVE_LEAK	X86_BUG(6) /* FXSAVE leaks FOP/FIP/FOP */
 #define X86_BUG_CLFLUSH_MONITOR	X86_BUG(7) /* AAI65, CLFLUSH required before MONITOR */
 #define X86_BUG_SYSRET_SS_ATTRS	X86_BUG(8) /* SYSRET doesn't fix up SS attrs */
+#define X86_BUG_SWAPGS_MFENCE	X86_BUG(9) /* SWAPGS may need MFENCE */
 
 #ifdef CONFIG_X86_32
 /*
diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 97c59fd..9cd932b 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -589,6 +589,9 @@ static void init_amd_k8(struct cpuinfo_x86 *c)
 	if ((level >= 0x0f48 && level < 0x0f50) || level >= 0x0f58)
 		set_cpu_cap(c, X86_FEATURE_REP_GOOD);
 
+	/* Early steppings needed a mfence on swapgs. */
+	set_cpu_bug(c, X86_BUG_SWAPGS_MFENCE);
+
 	/*
 	 * Some BIOSes incorrectly force this feature, but only K8 revision D
 	 * (model = 0x14) and later actually support it.
-- 
2.5.5

  parent reply	other threads:[~2016-03-21 16:16 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-21 16:16 Updated version of RD/WR FS/GS BASE patchkit Andi Kleen
2016-03-21 16:16 ` [PATCH 1/9] x86: Add intrinsics/macros for new rd/wr fs/gs base instructions Andi Kleen
2016-03-21 18:14   ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 2/9] x86: Add support for rd/wr fs/gs base Andi Kleen
2016-03-21 18:13   ` Andy Lutomirski
2016-03-21 19:05     ` Andi Kleen
2016-03-21 19:22       ` Andy Lutomirski
2016-03-21 22:05     ` Andi Kleen
2016-03-21 22:08       ` Andy Lutomirski
2016-03-21 22:15         ` Andi Kleen
2016-03-22  8:36           ` Thomas Gleixner
2016-03-22 14:40           ` Brian Gerst
2016-04-15  0:06   ` Andy Lutomirski
2016-03-21 16:16 ` Andi Kleen [this message]
2016-03-21 16:16 ` [PATCH 4/9] x86: Enumerate kernel FSGS capability in AT_HWCAP2 Andi Kleen
2016-03-21 18:49   ` Brian Gerst
2016-03-21 18:54     ` Andi Kleen
2016-03-21 19:32       ` Brian Gerst
2016-03-21 19:43         ` Andi Kleen
2016-03-21 22:10           ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 5/9] x86: Add documentation for rd/wr fs/gs base Andi Kleen
2016-03-23 19:14   ` Valdis.Kletnieks
2016-03-21 16:16 ` [PATCH 6/9] x86: Use rd/wr fs/gs base in arch_prctl Andi Kleen
2016-03-21 18:17   ` Andy Lutomirski
2016-03-21 16:16 ` [PATCH 7/9] x86: Add self test code for fsgsbase Andi Kleen
2016-03-21 16:16 ` [PATCH 8/9] x86: Support arbitrary fs/gs base in getregs Andi Kleen
2016-03-21 16:16 ` [PATCH 9/9] x86: Save FS/GS base in core dump Andi Kleen
2016-03-21 18:39 ` Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski
2016-03-21 19:03   ` Andi Kleen
2016-03-21 19:23     ` Andy Lutomirski
2016-03-21 19:40       ` Andi Kleen
2016-03-21 22:05         ` Andy Lutomirski
2016-03-21 22:11           ` Andi Kleen
2016-03-21 22:27             ` Andy Lutomirski
2016-03-21 22:41               ` Andi Kleen
2016-03-21 22:47                 ` Andy Lutomirski
2016-03-21 22:52                   ` Andi Kleen
2016-03-21 22:57                     ` Andy Lutomirski
2016-03-21 23:02                       ` Andi Kleen

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