> On Oct 12, 2021, at 3:16 AM, Peter Xu <peterx@xxxxxxxxxx> 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); >> + tlb_gather_mmu(&tlb, mm); >> + tlb_start_vma(&tlb, vma); > > Pure question: > > I actually have no idea why tlb_start_vma() is needed here, as protection range > can be just a single page, but anyway.. I do see that tlb_start_vma() contains > a whole-vma flush_cache_range() when the arch needs it, then does it mean that > besides the inc_tlb_flush_pending() to be dropped, so as to the other call to > flush_cache_range() above? Good point. tlb_start_vma() and tlb_end_vma() are required since some archs do not batch TLB flushes across VMAs (e.g., ARM). I am not sure whether that’s the best behavior for all archs, but I do not want to change it. Anyhow, you make a valid point that the flush_cache_range() should be dropped as well. I will do so for next version. Regards, Nadav
