Hi Andy, 2016-01-09 7:15 GMT+08:00 Andy Lutomirski <luto@xxxxxxxxxx>: > When switch_mm activates a new pgd, it also sets a bit that tells > other CPUs that the pgd is in use so that tlb flush IPIs will be > sent. In order for that to work correctly, the bit needs to be > visible prior to loading the pgd and therefore starting to fill the > local TLB. > > Document all the barriers that make this work correctly and add a > couple that were missing. > > Cc: stable@xxxxxxxxxxxxxxx > Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx> > --- > arch/x86/include/asm/mmu_context.h | 33 ++++++++++++++++++++++++++++++++- > arch/x86/mm/tlb.c | 29 ++++++++++++++++++++++++++--- > 2 files changed, 58 insertions(+), 4 deletions(-) > > diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h > index 379cd3658799..1edc9cd198b8 100644 > --- a/arch/x86/include/asm/mmu_context.h > +++ b/arch/x86/include/asm/mmu_context.h > @@ -116,8 +116,34 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, > #endif > cpumask_set_cpu(cpu, mm_cpumask(next)); > > - /* Re-load page tables */ > + /* > + * Re-load page tables. > + * > + * This logic has an ordering constraint: > + * > + * CPU 0: Write to a PTE for 'next' > + * CPU 0: load bit 1 in mm_cpumask. if nonzero, send IPI. > + * CPU 1: set bit 1 in next's mm_cpumask > + * CPU 1: load from the PTE that CPU 0 writes (implicit) > + * > + * We need to prevent an outcome in which CPU 1 observes > + * the new PTE value and CPU 0 observes bit 1 clear in > + * mm_cpumask. (If that occurs, then the IPI will never > + * be sent, and CPU 0's TLB will contain a stale entry.) I misunderstand this comments, CPU0 write to a PTE for 'next', and CPU0 observes bit 1 clear in mm_cpumask, so CPU0 won't kick IPI to CPU1, why CPU0's TLB will contain a stale entry instead of CPU1? Regards, Wanpeng Li -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>