Hi Anshuman,

On 7/22/21 1:51 PM, Anshuman Khandual wrote:

Small nit:

s/Fix corrupted page flag/Fix page flag corruption on arm64/

Sure, The replacement will be applied in v4, thanks!

On 7/21/21 5:33 PM, Gavin Shan wrote:

quoted

Hi Anshuman,

On 7/21/21 8:18 PM, Anshuman Khandual wrote:

quoted

On 7/19/21 6:36 PM, Gavin Shan wrote:

quoted

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.

But also some in code comments where flush_dcache_page() is being called.

Yes, I will add some comments where flush_dcache_page() is called in v4.

Thanks,
Gavin