Commit-ID: 22c4bd9fa921c2b1b3f2420d7b9dabbe982f3059 Gitweb: http://git.kernel.org/tip/22c4bd9fa921c2b1b3f2420d7b9dabbe982f3059 Author: Andy Lutomirski <luto@xxxxxxxxxxxxxx> AuthorDate: Fri, 24 Oct 2014 15:58:09 -0700 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Wed, 4 Feb 2015 12:10:43 +0100 x86: Add a comment clarifying LDT context switching The code is correct, but only for a rather subtle reason. This confused me for quite a while when I read switch_mm, so clarify the code to avoid confusing other people, too. TBH, I wouldn't be surprised if this code was only correct by accident. Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Reviewed-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Vince Weaver <vince@xxxxxxxxxx> Cc: "hillf.zj" <hillf.zj@xxxxxxxxxxxxxxx> Cc: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Link: http://lkml.kernel.org/r/0db86397f968996fb772c443c251415b0b430ddd.1414190806.git.luto@xxxxxxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/include/asm/mmu_context.h | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h index 4b75d59..52c1835 100644 --- a/arch/x86/include/asm/mmu_context.h +++ b/arch/x86/include/asm/mmu_context.h @@ -55,12 +55,14 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, /* * Load the LDT, if the LDT is different. * - * It's possible leave_mm(prev) has been called. If so, - * then prev->context.ldt could be out of sync with the - * LDT descriptor or the LDT register. This can only happen - * if prev->context.ldt is non-null, since we never free - * an LDT. But LDTs can't be shared across mms, so - * prev->context.ldt won't be equal to next->context.ldt. + * It's possible that prev->context.ldt doesn't match + * the LDT register. This can happen if leave_mm(prev) + * was called and then modify_ldt changed + * prev->context.ldt but suppressed an IPI to this CPU. + * In this case, prev->context.ldt != NULL, because we + * never free an LDT while the mm still exists. That + * means that next->context.ldt != prev->context.ldt, + * because mms never share an LDT. */ if (unlikely(prev->context.ldt != next->context.ldt)) load_LDT_nolock(&next->context); -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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