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Date: Wed, 21 Jul 2021 22:03:39 +1000 From: Gavin Shan <gshan@...hat.com> To: Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org Cc: linux-kernel@...r.kernel.org, catalin.marinas@....com, will@...nel.org, akpm@...ux-foundation.org, chuhu@...hat.com, shan.gavin@...il.com Subject: Re: [PATCH v3 12/12] mm/debug_vm_pgtable: Fix corrupted page flag Hi Anshuman, On 7/21/21 8:18 PM, Anshuman Khandual wrote: > On 7/19/21 6:36 PM, Gavin Shan wrote: >> In page table entry modifying tests, set_xxx_at() are used to populate >> the page table entries. On ARM64, PG_arch_1 is set to the target page >> flag if execution permission is given. The page flag is kept when the >> page is free'd to buddy's free area list. However, it will trigger page >> checking failure when it's pulled from the buddy's free area list, as >> the following warning messages indicate. >> >> BUG: Bad page state in process memhog pfn:08000 >> page:0000000015c0a628 refcount:0 mapcount:0 \ >> mapping:0000000000000000 index:0x1 pfn:0x8000 >> flags: 0x7ffff8000000800(arch_1|node=0|zone=0|lastcpupid=0xfffff) >> raw: 07ffff8000000800 dead000000000100 dead000000000122 0000000000000000 >> raw: 0000000000000001 0000000000000000 00000000ffffffff 0000000000000000 >> page dumped because: PAGE_FLAGS_CHECK_AT_PREP flag(s) set >> >> This fixes the issue by clearing PG_arch_1 through flush_dcache_page() >> after set_xxx_at() is called. > > Could you please add comments before each flush_dcache_page() instance > explaining why this is needed for arm64 platforms with relevant PG_arch_1 > context and how this does not have any adverse effect on other platforms ? > It should be easy for some one looking at this code after a while to figure > out from where flush_dcache_page() came from. > Good point. I will improve chage log to include the commit ID in v4 where the page flag (PG_arch_1) is used and explain how. In that case, it's much clearer to understand the reason why we need flush_dcache_page() after set_xxx_at() on ARM64. Thanks, Gavin
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