On Thu, Dec 10, 2020 at 12:11:07PM +0000, Will Deacon wrote:
> Passing the range '0, -1' to tlb_gather_mmu() sets the 'fullmm' flag,
> which indicates that the mm_struct being operated on is going away. In
> this case, some architectures (such as arm64) can elide TLB invalidation
> by ensuring that the TLB tag (ASID) associated with this mm is not
> immediately reclaimed. Although this behaviour is documented in
> asm-generic/tlb.h, it's subtle and easily missed.
>
> Introduce tlb_gather_mmu_fullmm() to make it clearer that this is for the
> entire mm and WARN() if tlb_gather_mmu() is called with the 'fullmm'
> address range.
>
> Signed-off-by: Will Deacon <will@xxxxxxxxxx>
> ---
> include/asm-generic/tlb.h | 6 ++++--
> include/linux/mm_types.h | 1 +
> mm/mmap.c | 2 +-
> mm/mmu_gather.c | 16 ++++++++++++++--
> 4 files changed, 20 insertions(+), 5 deletions(-)
>
> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> index 6661ee1cff47..2c68a545ffa7 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -46,7 +46,9 @@
> *
> * The mmu_gather API consists of:
> *
> - * - tlb_gather_mmu() / tlb_finish_mmu(); start and finish a mmu_gather
> + * - tlb_gather_mmu() / tlb_gather_mmu_fullmm() / tlb_finish_mmu()
> + *
> + * start and finish a mmu_gather
> *
> * Finish in particular will issue a (final) TLB invalidate and free
> * all (remaining) queued pages.
> @@ -91,7 +93,7 @@
> *
> * - mmu_gather::fullmm
> *
> - * A flag set by tlb_gather_mmu() to indicate we're going to free
> + * A flag set by tlb_gather_mmu_fullmm() to indicate we're going to free
> * the entire mm; this allows a number of optimizations.
> *
> * - We can ignore tlb_{start,end}_vma(); because we don't
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index 7b90058a62be..42231729affe 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -585,6 +585,7 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
> struct mmu_gather;
> extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> unsigned long start, unsigned long end);
> +extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
> extern void tlb_finish_mmu(struct mmu_gather *tlb);
>
> static inline void init_tlb_flush_pending(struct mm_struct *mm)
> diff --git a/mm/mmap.c b/mm/mmap.c
> index a3e5854cd01e..cdd3dae6547c 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -3214,7 +3214,7 @@ void exit_mmap(struct mm_struct *mm)
>
> lru_add_drain();
> flush_cache_mm(mm);
> - tlb_gather_mmu(&tlb, mm, 0, -1);
> + tlb_gather_mmu_fullmm(&tlb, mm);
> /* update_hiwater_rss(mm) here? but nobody should be looking */
> /* Use -1 here to ensure all VMAs in the mm are unmapped */
> unmap_vmas(&tlb, vma, 0, -1);
> diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c
> index b0be5a7aa08f..5f5e45d9eb50 100644
> --- a/mm/mmu_gather.c
> +++ b/mm/mmu_gather.c
> @@ -261,8 +261,8 @@ void tlb_flush_mmu(struct mmu_gather *tlb)
> * respectively when @mm is without users and we're going to destroy
> * the full address space (exit/execve).
> */
> -void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> - unsigned long start, unsigned long end)
> +static void __tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> + unsigned long start, unsigned long end)
> {
> tlb->mm = mm;
>
> @@ -287,6 +287,18 @@ void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> inc_tlb_flush_pending(tlb->mm);
> }
>
> +void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm,
> + unsigned long start, unsigned long end)
> +{
> + WARN_ON(!(start | (end + 1))); /* Use _fullmm() instead */
> + __tlb_gather_mmu(tlb, mm, start, end);
> +}
> +
> +void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm)
> +{
> + __tlb_gather_mmu(tlb, mm, 0, -1);
> +}
> +
IMO, there is no point adding the wrappers given you will remove
the WARN_ON in the next patch.
But if you prefer, they should be at least moved to the header for
inlining.
Consider this whole series
Reviewed-by: Yu Zhao <yuzhao@xxxxxxxxxx>
