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Wed, 9 Apr 2025 09:08:27 +0800 Message-ID: Date: Wed, 9 Apr 2025 09:08:27 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird CC: , , , , , , , , , , , , , , Subject: Re: [PATCH] arm64: dax: add devmap check for pmd_trans_huge To: References: <20250408085914.1946183-1-mawupeng1@huawei.com> From: mawupeng In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.114] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemg100017.china.huawei.com (7.202.181.58) X-Rspamd-Queue-Id: C5E442000F X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: p4saq7g1csjetmak78b7csuq8mgsgyrx X-HE-Tag: 1744160913-655045 X-HE-Meta: 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 cVOmPd7K seG1y+bJZZfZcQ+WyTeqrJd30Fvy3Pf/1tJxBwzzY8BAYS4xZC8TubvLTTf9FPW87IEENn9jFQpUCo76vYW7d/FcryWRjxs8JDBvOgrmabQESA046jG/k9kPAgvWd/5O1d7yL2CeBUt573+JuvtbYev02zEuTsqH7UfBtjuCmcARxcYWseoSKezkzf7JWEFi78gC1EzSzIS7QsM5m8Z+mWdz/rItAvWcxaoGeMGuMAZb+3okDiOShJwBiDw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/4/9 7:05, Alistair Popple wrote: > On Tue, Apr 08, 2025 at 04:59:14PM +0800, Wupeng Ma wrote: >> During our test in ext4 dax linux-v5.10 on arm64. A BUG_ON is trigger in >> follow_invalidate_pte as follow since this pmd is seem as pmd_trans_huge. >> However this page is really a dax-pmds rather than a pmd trans huge. >> >> Call trace is shown as follow: >> >> ------------[ cut here ]------------ >> kernel BUG at mm/memory.c:5185! >> CPU: 0 PID: 150 Comm: kworker/u8:10 Not tainted 5.10.0-01678-g1e62aad66bbc-dirty #36 > > This is an old kernel, and I couldn't correlate the line number of the BUG_ON() > probably because you have patches applied. But I assume this is the VM_BUG_ON() > in follow_invalidate_pte()? Does this issue reproduce on more recent kernel Yes. > versions (eg. v6.13)? Or some other upstream kernel version? Since Commit 06083a0921fd ("dax: fix missing writeprotect the pte entry"), the same issue can not be trigger in the same call trace. However the same issue may still exist in current kernel. > >> pc : follow_invalidate_pte+0xdc/0x5e0 >> lr : follow_invalidate_pte+0xc4/0x5e0 >> sp : ffffa00012997110 >> Call trace: >> follow_invalidate_pte+0xdc/0x5e0 >> dax_entry_mkclean+0x250/0x870 >> dax_writeback_one+0xac/0x380 >> dax_writeback_mapping_range+0x22c/0x704 >> ext4_dax_writepages+0x234/0x6e4 >> do_writepages+0xc8/0x1c0 >> __writeback_single_inode+0xb8/0x560 >> writeback_sb_inodes+0x344/0x7a0 >> wb_writeback+0x1f8/0x6b0 >> wb_do_writeback+0x194/0x3cc >> wb_workfn+0x14c/0x590 >> process_one_work+0x470/0xa30 >> worker_thread+0xac/0x510 >> kthread+0x1e0/0x220 >> ret_from_fork+0x10/0x18 >> ---[ end trace 0f479050bd4b1818 ]--- >> Kernel panic - not syncing: Oops - BUG: Fatal exception >> ---[ end Kernel panic - not syncing: Oops - BUG: Fatal exception ]--- >> >> Commit 5c7fb56e5e3f ("mm, dax: dax-pmd vs thp-pmd vs hugetlbfs-pmd") and >> commit 36b78402d97a ("powerpc/hash64/devmap: Use H_PAGE_THP_HUGE when >> setting up huge devmap PTE entries") already check pmd_devmap during >> checking pmd_trans_huge. Since pmd_devmap() is used to distinguish dax-pmds, >> add the same check for arm64 to fix this problem. > > That seems correct to me. In practice most callers of pmd_trans_huge() that can > see a dax-pmd already check for it explicitly with vma_is_dax(), but there are a > few cases that don't. > >> Add PTE_DEVMAP in pte_modify as commit 4628a64591e6 ("mm: Preserve >> _PAGE_DEVMAP across mprotect() calls") does to avoid the same issue in >> mprotect. >> >> Fixes: 73b20c84d42d ("arm64: mm: implement pte_devmap support") >> Signed-off-by: Wupeng Ma >> --- >> arch/arm64/include/asm/pgtable.h | 5 +++-- >> 1 file changed, 3 insertions(+), 2 deletions(-) >> >> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h >> index d3b538be1500b..b9a618127c01b 100644 >> --- a/arch/arm64/include/asm/pgtable.h >> +++ b/arch/arm64/include/asm/pgtable.h >> @@ -740,7 +740,7 @@ static inline int pmd_trans_huge(pmd_t pmd) >> * as a table, so force the valid bit for the comparison. >> */ >> return pmd_val(pmd) && pmd_present(pmd) && >> - !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID)); >> + !pmd_table(__pmd(pmd_val(pmd) | PTE_VALID)) && !pmd_devmap(pmd); >> } >> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */ >> >> @@ -1186,7 +1186,8 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot) >> */ >> const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY | >> PTE_PRESENT_INVALID | PTE_VALID | PTE_WRITE | >> - PTE_GP | PTE_ATTRINDX_MASK | PTE_PO_IDX_MASK; >> + PTE_GP | PTE_ATTRINDX_MASK | PTE_PO_IDX_MASK | >> + PTE_DEVMAP; >> >> /* preserve the hardware dirty information */ >> if (pte_hw_dirty(pte)) >> -- >> 2.43.0 >> >>