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Date: Sun, 12 May 2013 22:14:51 -0700
From: Joe Damato <ice799@...il.com>
To: x86@...nel.org, linux-kernel@...r.kernel.org
Cc: mingo@...hat.com, hpa@...or.com, akpm@...ux-foundation.org,
Joe Damato <ice799@...il.com>
Subject: [PATCH] x86: Reduce duplicated code in the x86_64 context switch path.
Signed-off-by: Joe Damato <ice799@...il.com>
---
arch/x86/include/asm/switch_to.h | 30 ++++++++++++++++++++++++++++++
arch/x86/kernel/process_64.c | 29 ++---------------------------
2 files changed, 32 insertions(+), 27 deletions(-)
diff --git a/arch/x86/include/asm/switch_to.h b/arch/x86/include/asm/switch_to.h
index 4ec45b3..a322cc6 100644
--- a/arch/x86/include/asm/switch_to.h
+++ b/arch/x86/include/asm/switch_to.h
@@ -124,6 +124,36 @@ do { \
__switch_canary_iparam \
: "memory", "cc" __EXTRA_CLOBBER)
+#define loadsegment_fs(fs, index) \
+ loadsegment(fs, index)
+
+#define loadsegment_gs(gs, index) \
+ load_gs_index(index)
+
+#define switch_segment(prev, next, index, seg, msr) \
+ do { \
+ /* \
+ * Segment register != 0 always requires a reload. Also \
+ * reload when it has changed. When prev process used 64bit \
+ * base always reload to avoid an information leak. \
+ */ \
+ if (unlikely(index | next->index | prev->seg)) { \
+ loadsegment_##seg(seg, next->index); \
+ /* \
+ * Check if the user used a selector != 0; if yes \
+ * clear 64bit base, since overloaded base is always \
+ * mapped to the Null selector \
+ */ \
+ if (index) \
+ prev->seg = 0; \
+ } \
+ \
+ /* when next process has a 64bit base use it */ \
+ if (next->seg) \
+ wrmsrl(msr, next->seg); \
+ prev->index = index; \
+ } while (0)
+
#endif /* CONFIG_X86_32 */
#endif /* _ASM_X86_SWITCH_TO_H */
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 355ae06..f41d026 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -318,34 +318,9 @@ __switch_to(struct task_struct *prev_p, struct task_struct *next_p)
/*
* Switch FS and GS.
- *
- * Segment register != 0 always requires a reload. Also
- * reload when it has changed. When prev process used 64bit
- * base always reload to avoid an information leak.
*/
- if (unlikely(fsindex | next->fsindex | prev->fs)) {
- loadsegment(fs, next->fsindex);
- /*
- * Check if the user used a selector != 0; if yes
- * clear 64bit base, since overloaded base is always
- * mapped to the Null selector
- */
- if (fsindex)
- prev->fs = 0;
- }
- /* when next process has a 64bit base use it */
- if (next->fs)
- wrmsrl(MSR_FS_BASE, next->fs);
- prev->fsindex = fsindex;
-
- if (unlikely(gsindex | next->gsindex | prev->gs)) {
- load_gs_index(next->gsindex);
- if (gsindex)
- prev->gs = 0;
- }
- if (next->gs)
- wrmsrl(MSR_KERNEL_GS_BASE, next->gs);
- prev->gsindex = gsindex;
+ switch_segment(prev, next, fsindex, fs, MSR_FS_BASE);
+ switch_segment(prev, next, gsindex, gs, MSR_KERNEL_GS_BASE);
switch_fpu_finish(next_p, fpu);
--
1.7.9.5
--
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