On Sun, May 12, 2013 at 11:03 PM, H. Peter Anvin <h...@zytor.com> wrote:
> This is a net addition in code, and send to only make it harder to understand
> what is happening. As such I don't think this is a good idea.
OK, I tweaked it slightly to break even on lines of code sent a v2. I
do think it would be nice to remove the duplicated code and (IMHO) it
makes __switch_to easier to read.
> Joe Damato <ice...@gmail.com> wrote:
>
>>Signed-off-by: Joe Damato <ice...@gmail.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);
>>
>
> --
> Sent from my mobile phone. Please excuse brevity and lack of formatting.
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