From: Peter Zijlstra <peterz@infradead.org>
To: Nadav Amit <nadav.amit@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>, Peter Xu <peterx@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>, Yu Zhao <yuzhao@google.com>,
Nick Piggin <npiggin@gmail.com>,
x86@kernel.org
Subject: Re: [PATCH 1/2] mm/mprotect: use mmu_gather
Date: Tue, 5 Oct 2021 08:53:35 +0200 [thread overview]
Message-ID: <20211005065335.GG4323@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <620B1A38-1457-4F77-8666-E73A318392B6@gmail.com>
On Mon, Oct 04, 2021 at 12:24:14PM -0700, Nadav Amit wrote:
>
>
> > 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.
-ENOPARSE, did you read decrement as comment? In any case, I don't
particularly care about the comment, and tlb_*_mmu() imply the inc/dec
thingies.
All I tried to do is point out that removing the dec but leaving the inc
is somewhat inconsistent :-)
next prev parent reply other threads:[~2021-10-05 6:55 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-25 20:54 [PATCH 0/2] mm/mprotect: avoid unnecessary TLB flushes Nadav Amit
2021-09-25 20:54 ` [PATCH 1/2] mm/mprotect: use mmu_gather Nadav Amit
2021-10-03 12:10 ` Peter Zijlstra
2021-10-04 19:24 ` Nadav Amit
2021-10-05 6:53 ` Peter Zijlstra [this message]
2021-10-05 16:34 ` Nadav Amit
2021-10-11 3:45 ` Nadav Amit
2021-10-12 10:16 ` Peter Xu
2021-10-12 17:31 ` Nadav Amit
2021-10-12 23:20 ` Peter Xu
2021-10-13 15:59 ` Nadav Amit
2021-09-25 20:54 ` [PATCH 2/2] mm/mprotect: do not flush on permission promotion Nadav Amit
2021-10-07 12:13 ` David Hildenbrand
2021-10-07 16:16 ` Nadav Amit
2021-10-07 17:07 ` David Hildenbrand
2021-10-08 6:06 ` Nadav Amit
2021-10-08 7:35 ` David Hildenbrand
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