From: Andrew Morton <akpm@linux-foundation.org>
To: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: mike.kravetz@oracle.com, catalin.marinas@arm.com,
will@kernel.org, songmuchun@bytedance.com,
tsbogend@alpha.franken.de, James.Bottomley@HansenPartnership.com,
deller@gmx.de, mpe@ellerman.id.au, benh@kernel.crashing.org,
paulus@samba.org, hca@linux.ibm.com, gor@linux.ibm.com,
agordeev@linux.ibm.com, borntraeger@linux.ibm.com,
svens@linux.ibm.com, ysato@users.osdn.me, dalias@libc.org,
davem@davemloft.net, arnd@arndb.de,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-ia64@vger.kernel.org,
linux-mips@vger.kernel.org, linux-parisc@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-arch@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v3 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration
Date: Tue, 10 May 2022 16:17:39 -0700 [thread overview]
Message-ID: <20220510161739.fdea4d78dde8471033aab22b@linux-foundation.org> (raw)
In-Reply-To: <ea5abf529f0997b5430961012bfda6166c1efc8c.1652147571.git.baolin.wang@linux.alibaba.com>
On Tue, 10 May 2022 11:45:59 +0800 Baolin Wang <baolin.wang@linux.alibaba.com> wrote:
> On some architectures (like ARM64), it can support CONT-PTE/PMD size
> hugetlb, which means it can support not only PMD/PUD size hugetlb:
> 2M and 1G, but also CONT-PTE/PMD size: 64K and 32M if a 4K page
> size specified.
>
> When migrating a hugetlb page, we will get the relevant page table
> entry by huge_pte_offset() only once to nuke it and remap it with
> a migration pte entry. This is correct for PMD or PUD size hugetlb,
> since they always contain only one pmd entry or pud entry in the
> page table.
>
> However this is incorrect for CONT-PTE and CONT-PMD size hugetlb,
> since they can contain several continuous pte or pmd entry with
> same page table attributes. So we will nuke or remap only one pte
> or pmd entry for this CONT-PTE/PMD size hugetlb page, which is
> not expected for hugetlb migration. The problem is we can still
> continue to modify the subpages' data of a hugetlb page during
> migrating a hugetlb page, which can cause a serious data consistent
> issue, since we did not nuke the page table entry and set a
> migration pte for the subpages of a hugetlb page.
>
> To fix this issue, we should change to use huge_ptep_clear_flush()
> to nuke a hugetlb page table, and remap it with set_huge_pte_at()
> and set_huge_swap_pte_at() when migrating a hugetlb page, which
> already considered the CONT-PTE or CONT-PMD size hugetlb.
>
> ...
>
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -1093,6 +1093,17 @@ static inline void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr
> pte_t *ptep, pte_t pte, unsigned long sz)
> {
> }
> +
> +static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep)
> +{
> + return ptep_get(ptep);
> +}
> +
> +static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, pte_t pte)
> +{
> +}
> #endif /* CONFIG_HUGETLB_PAGE */
>
This blows up nommu (arm allnoconfig):
In file included from fs/io_uring.c:71:
./include/linux/hugetlb.h: In function 'huge_ptep_clear_flush':
./include/linux/hugetlb.h:1100:16: error: implicit declaration of function 'ptep_get' [-Werror=implicit-function-declaration]
1100 | return ptep_get(ptep);
| ^~~~~~~~
huge_ptep_clear_flush() is only used in CONFIG_NOMMU=n files, so I simply
zapped this change.
--- a/include/linux/hugetlb.h~mm-rmap-fix-cont-pte-pmd-size-hugetlb-issue-when-migration-fix
+++ a/include/linux/hugetlb.h
@@ -1093,17 +1093,6 @@ static inline void set_huge_swap_pte_at(
pte_t *ptep, pte_t pte, unsigned long sz)
{
}
-
-static inline pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
- unsigned long addr, pte_t *ptep)
-{
- return ptep_get(ptep);
-}
-
-static inline void set_huge_pte_at(struct mm_struct *mm, unsigned long addr,
- pte_t *ptep, pte_t pte)
-{
-}
#endif /* CONFIG_HUGETLB_PAGE */
static inline spinlock_t *huge_pte_lock(struct hstate *h,
_
next prev parent reply other threads:[~2022-05-10 23:17 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-10 3:45 [PATCH v3 0/3] Fix CONT-PTE/PMD size hugetlb issue when unmapping or migrating Baolin Wang
2022-05-10 3:45 ` [PATCH v3 1/3] mm: change huge_ptep_clear_flush() to return the original pte Baolin Wang
2022-05-10 3:45 ` [PATCH v3 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration Baolin Wang
2022-05-10 23:17 ` Andrew Morton [this message]
2022-05-10 23:28 ` Andrew Morton
2022-05-11 3:59 ` Baolin Wang
2022-05-11 1:19 ` kernel test robot
2022-05-11 2:04 ` Andrew Morton
2022-05-10 3:46 ` [PATCH v3 3/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when unmapping Baolin Wang
2022-05-10 4:04 ` [PATCH v3 0/3] Fix CONT-PTE/PMD size hugetlb issue when unmapping or migrating Andrew Morton
2022-05-10 4:26 ` Baolin Wang
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