Re: [PATCH 1/2] mm/mprotect: use mmu_gather

Nadav Amit
2021-10-04T19:24:21Z

> On Oct 3, 2021, at 5:10 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sat, Sep 25, 2021 at 01:54:22PM -0700, Nadav Amit wrote:
>
>> @@ -338,25 +344,25 @@ static unsigned long change_protection_range(struct vm_area_struct *vma,
>> struct mm_struct *mm = vma->vm_mm;
>> pgd_t *pgd;
>> unsigned long next;
>> - unsigned long start = addr;
>> unsigned long pages = 0;
>> + struct mmu_gather tlb;
>>
>> BUG_ON(addr >= end);
>> pgd = pgd_offset(mm, addr);
>> flush_cache_range(vma, addr, end);
>> inc_tlb_flush_pending(mm);
>
> That seems unbalanced...

Bad rebase. Thanks for catching it!

>
>> + tlb_gather_mmu(&tlb, mm);
>> + tlb_start_vma(&tlb, vma);
>> do {
>> next = pgd_addr_end(addr, end);
>> if (pgd_none_or_clear_bad(pgd))
>> continue;
>> - pages += change_p4d_range(vma, pgd, addr, next, newprot,
>> + pages += change_p4d_range(&tlb, vma, pgd, addr, next, newprot,
>> cp_flags);
>> } while (pgd++, addr = next, addr != end);
>>
>> - /* Only flush the TLB if we actually modified any entries: */
>> - if (pages)
>> - flush_tlb_range(vma, start, end);
>> - dec_tlb_flush_pending(mm);
>
> ... seeing you do remove the extra decrement.

Is it really needed? We do not put this comment elsewhere for
tlb_finish_mmu(). But no problem, I’ll keep it.