Re: [PATCH V10] mm/debug: Add tests validating architecture page table helpers

[Anshuman Khandual]

On 11/20/2019 11:01 AM, Anshuman Khandual wrote:
> This adds tests which will validate architecture page table helpers and
> other accessors in their compliance with expected generic MM semantics.
> This will help various architectures in validating changes to existing
> page table helpers or addition of new ones.
> 
> This test covers basic page table entry transformations including but not
> limited to old, young, dirty, clean, write, write protect etc at various
> level along with populating intermediate entries with next page table page
> and validating them.
> 
> Test page table pages are allocated from system memory with required size
> and alignments. The mapped pfns at page table levels are derived from a
> real pfn representing a valid kernel text symbol. This test gets called
> right after page_alloc_init_late().
> 
> This gets build and run when CONFIG_DEBUG_VM_PGTABLE is selected along with
> CONFIG_VM_DEBUG. Architectures willing to subscribe this test also need to
> select CONFIG_ARCH_HAS_DEBUG_VM_PGTABLE which for now is limited to x86 and
> arm64. Going forward, other architectures too can enable this after fixing
> build or runtime problems (if any) with their page table helpers.
> 
> Folks interested in making sure that a given platform's page table helpers
> conform to expected generic MM semantics should enable the above config
> which will just trigger this test during boot. Any non conformity here will
> be reported as an warning which would need to be fixed. This test will help
> catch any changes to the agreed upon semantics expected from generic MM and
> enable platforms to accommodate it thereafter.
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
> Cc: Jason Gunthorpe <jgg@xxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Mark Brown <broonie@xxxxxxxxxx>
> Cc: Steven Price <Steven.Price@xxxxxxx>
> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> Cc: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Sri Krishna chowdary <schowdary@xxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Russell King - ARM Linux <linux@xxxxxxxxxxxxxxx>
> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
> Cc: Paul Mackerras <paulus@xxxxxxxxx>
> Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
> Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
> Cc: James Hogan <jhogan@xxxxxxxxxx>
> Cc: Paul Burton <paul.burton@xxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill@xxxxxxxxxxxxx>
> Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: linux-snps-arc@xxxxxxxxxxxxxxxxxxx
> Cc: linux-mips@xxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-ia64@xxxxxxxxxxxxxxx
> Cc: linuxppc-dev@xxxxxxxxxxxxxxxx
> Cc: linux-s390@xxxxxxxxxxxxxxx
> Cc: linux-sh@xxxxxxxxxxxxxxx
> Cc: sparclinux@xxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> 
> Tested-by: Christophe Leroy <christophe.leroy@xxxxxx>		#PPC32
> Reviewed-by: Ingo Molnar <mingo@xxxxxxxxxx>
> Suggested-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxx>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
> This adds a test validation for architecture exported page table helpers.
> Patch adds basic transformation tests at various levels of the page table.
> 
> This test was originally suggested by Catalin during arm64 THP migration
> RFC discussion earlier. Going forward it can include more specific tests
> with respect to various generic MM functions like THP, HugeTLB etc and
> platform specific tests.
> 
> https://lore.kernel.org/linux-mm/20190628102003.GA56463@xxxxxxxxxxxxxxxxxxxx/
> 
> Needs to be applied on linux-next (next-20191108).
> 
> Changes in V10:
> 
> - Always enable DEBUG_VM_PGTABLE when DEBUG_VM is enabled per Ingo
> - Added tags from Ingo

Hello Andrew,

There has not been any further comments on the previous version (V9) or this version
(V10) of the patch which accommodated a comment from Ingo Molnar regarding making
DEBUG_VM_PGTABLE always enabled when DEBUG_VM is selected. If this version looks okay,
then would you please consider merging ? But if there is anything which still needs
to be improved, please do let me know. I will try to incorporate that. Thank you.

- Anshuman