From: Will Deacon <firstname.lastname@example.org>
To: Steve Capper <email@example.com>
Cc: Catalin Marinas <firstname.lastname@example.org>,
David Hildenbrand <email@example.com>,
Mike Kravetz <firstname.lastname@example.org>,
"Aneesh Kumar K . V" <email@example.com>,
Peter Zijlstra <firstname.lastname@example.org>,
Subject: Re: VM_BUG_ON(!tlb->end) on munmap() with CONT hugetlb pages
Date: Fri, 6 May 2022 13:49:11 +0100 [thread overview]
Message-ID: <20220506124909.GA22892@willie-the-truck> (raw)
On Wed, Mar 23, 2022 at 04:34:26PM +0000, Steve Capper wrote:
> On 23/03/2022 16:21, Catalin Marinas wrote:
> > On Wed, Mar 23, 2022 at 11:51:25AM +0000, Steve Capper wrote:
> > > On 22/03/2022 17:56, Catalin Marinas wrote:
> > > > At a quick look, we wouldn't have a problem with missing TLB flushing
> > > > since huge_ptep_get_and_clear() does this for contiguous PTEs. Not sure
> > > > why it needs this though, Steve added it in commit d8bdcff28764. I think
> > > > we can defer this flushing to tlb_remove_page_size().
> > >
> > > The TLB flush in huge_ptep_get_and_clear() was added because it was called
> > > by hugetlb_change_protection() without any flushing. The concern was that,
> > > without the flush, it would be possible to get to different views of the
> > > same contiguous huge page. (Being contiguous they were not changed en masse
> > > atomically).
> > Maybe the code paths have been changed since but looking at
> > hugetlb_change_protection(), we have huge_ptep_modify_prot_start()
> > calling huge_ptep_get_and_clear() which AFAICT only needs to clear the
> > ptes. huge_ptep_modify_prot_commit() calls set_huge_pte_at() which does
> > another pte clearing + TLBI (clear_flush()) before setting the new ptes.
> > So we do the pte clearing and TLBI twice already.
> Thanks, yeah indeed the code has changed and the flush should be removed
> from the arm64 huge_ptep_get_and_clear.
Did anybody send a patch for this?
next prev parent reply other threads:[~2022-05-06 12:49 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-28 15:39 VM_BUG_ON(!tlb->end) on munmap() with CONT hugetlb pages David Hildenbrand
2022-03-01 0:26 ` Mike Kravetz
2022-03-07 23:06 ` Mike Kravetz
2022-03-21 16:34 ` David Hildenbrand
2022-03-22 17:56 ` Catalin Marinas
2022-03-23 11:51 ` Steve Capper
2022-03-23 16:21 ` Catalin Marinas
2022-03-23 16:34 ` Steve Capper
2022-03-23 17:21 ` Mike Kravetz
2022-05-06 12:49 ` Will Deacon [this message]
2022-05-09 11:19 ` Anshuman Khandual
2022-05-09 12:11 ` Catalin Marinas
2022-05-11 3:42 ` Anshuman Khandual
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