From: Catalin Marinas <catalin.marinas@arm.com>
To: Steve Capper <steve.capper@arm.com>
Cc: David Hildenbrand <david@redhat.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
anshuman.khandual@arm.com, Will Deacon <will@kernel.org>,
"Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
nd@arm.com
Subject: Re: VM_BUG_ON(!tlb->end) on munmap() with CONT hugetlb pages
Date: Wed, 23 Mar 2022 16:21:38 +0000 [thread overview]
Message-ID: <YjtJEjP9HJVEBq4w@arm.com> (raw)
In-Reply-To: <d05c6c9c-4d04-1ab0-0af7-4e79d416753d@arm.com>
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.
--
Catalin
next prev parent reply other threads:[~2022-03-23 16:21 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 [this message]
2022-03-23 16:34 ` Steve Capper
2022-03-23 17:21 ` Mike Kravetz
2022-05-06 12:49 ` Will Deacon
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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