| Message ID | 20230729131448.15531-1-yangyicong@huawei.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [-mm] arm64: tlbflush: Add some comments for TLB batched flushing | expand |
On Sat, Jul 29, 2023 at 09:14:48PM +0800, Yicong Yang wrote: > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h > index 3456866c6a1d..2bad230b95b4 100644 > --- a/arch/arm64/include/asm/tlbflush.h > +++ b/arch/arm64/include/asm/tlbflush.h > @@ -300,11 +300,26 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b > __flush_tlb_page_nosync(mm, uaddr); > } > > +/* > + * If mprotect/munmap/etc occurs during TLB batched flushing, we need to > + * synchronise all the TLBI issued by a DSB to avoid the race mentioned in Nitpick: s/by a DSB/with a DSB/ as it somehow reads that the DSB issued the TLBI. Since the rest of the series went in via the mm tree, I assume Andrew will pick this up as well. Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> Thanks.
Yicong Yang <yangyicong@huawei.com> writes: Thanks! I was reading this code the other day and it took me a while to figure out what was going on. These comments would have been very helpful and match my understanding, so: Reviewed-by: Alistair Popple <apopple@nvidia.com> > From: Yicong Yang <yangyicong@hisilicon.com> > > Add comments for arch_flush_tlb_batched_pending() and > arch_tlbbatch_flush() to illustrate why only a DSB is > needed. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> > --- > arch/arm64/include/asm/tlbflush.h | 15 +++++++++++++++ > 1 file changed, 15 insertions(+) > > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h > index 3456866c6a1d..2bad230b95b4 100644 > --- a/arch/arm64/include/asm/tlbflush.h > +++ b/arch/arm64/include/asm/tlbflush.h > @@ -300,11 +300,26 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b > __flush_tlb_page_nosync(mm, uaddr); > } > > +/* > + * If mprotect/munmap/etc occurs during TLB batched flushing, we need to > + * synchronise all the TLBI issued by a DSB to avoid the race mentioned in > + * flush_tlb_batched_pending(). > + */ > static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm) > { > dsb(ish); > } > > +/* > + * To support TLB batched flush for multiple pages unmapping, we only send > + * the TLBI for each page in arch_tlbbatch_add_pending() and wait for the > + * completion at the end in arch_tlbbatch_flush(). Since we've already issued > + * TLBI for each page so only a DSB is needed to synchronise its effect on the > + * other CPUs. > + * > + * This will save the time waiting on DSB comparing issuing a TLBI;DSB sequence > + * for each page. > + */ > static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) > { > dsb(ish);
diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h index 3456866c6a1d..2bad230b95b4 100644 --- a/arch/arm64/include/asm/tlbflush.h +++ b/arch/arm64/include/asm/tlbflush.h @@ -300,11 +300,26 @@ static inline void arch_tlbbatch_add_pending(struct arch_tlbflush_unmap_batch *b __flush_tlb_page_nosync(mm, uaddr); } +/* + * If mprotect/munmap/etc occurs during TLB batched flushing, we need to + * synchronise all the TLBI issued by a DSB to avoid the race mentioned in + * flush_tlb_batched_pending(). + */ static inline void arch_flush_tlb_batched_pending(struct mm_struct *mm) { dsb(ish); } +/* + * To support TLB batched flush for multiple pages unmapping, we only send + * the TLBI for each page in arch_tlbbatch_add_pending() and wait for the + * completion at the end in arch_tlbbatch_flush(). Since we've already issued + * TLBI for each page so only a DSB is needed to synchronise its effect on the + * other CPUs. + * + * This will save the time waiting on DSB comparing issuing a TLBI;DSB sequence + * for each page. + */ static inline void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) { dsb(ish);