On Tue, Oct 14, 2014 at 03:57:37PM -0700, Andy Lutomirski wrote: > 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 <l...@amacapital.net> > --- > arch/x86/include/asm/mmu_context.h | 11 ++++++++++- > 1 file changed, 10 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/include/asm/mmu_context.h > b/arch/x86/include/asm/mmu_context.h > index 166af2a8e865..04478103df37 100644 > --- a/arch/x86/include/asm/mmu_context.h > +++ b/arch/x86/include/asm/mmu_context.h > @@ -53,7 +53,16 @@ static inline void switch_mm(struct mm_struct *prev, > struct mm_struct *next, > /* Stop flush ipis for the previous mm */ > cpumask_clear_cpu(cpu, mm_cpumask(prev)); > > - /* Load the LDT, if the LDT is different: */ > + /* > + * 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
I'm staring at the code and trying to figure out where on the leave_mm() path this could happen. Got any code pointers? :-) > + * 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. > + */ > if (unlikely(prev->context.ldt != next->context.ldt)) > load_LDT_nolock(&next->context); > } > -- > 1.9.3 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- Regards/Gruss, Boris. -- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
