[PATCH V8] mm/debug: Add tests validating architecture page table helpers

[Anshuman Khandual]

On 10/28/2019 10:59 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 at linux-foundation.org>
> Cc: Vlastimil Babka <vbabka at suse.cz>
> Cc: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Cc: Mike Rapoport <rppt at linux.vnet.ibm.com>
> Cc: Jason Gunthorpe <jgg at ziepe.ca>
> Cc: Dan Williams <dan.j.williams at intel.com>
> Cc: Peter Zijlstra <peterz at infradead.org>
> Cc: Michal Hocko <mhocko at kernel.org>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Mark Brown <broonie at kernel.org>
> Cc: Steven Price <Steven.Price at arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Cc: Masahiro Yamada <yamada.masahiro at socionext.com>
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Tetsuo Handa <penguin-kernel at i-love.sakura.ne.jp>
> Cc: Matthew Wilcox <willy at infradead.org>
> Cc: Sri Krishna chowdary <schowdary at nvidia.com>
> Cc: Dave Hansen <dave.hansen at intel.com>
> Cc: Russell King - ARM Linux <linux at armlinux.org.uk>
> Cc: Michael Ellerman <mpe at ellerman.id.au>
> Cc: Paul Mackerras <paulus at samba.org>
> Cc: Martin Schwidefsky <schwidefsky at de.ibm.com>
> Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
> Cc: "David S. Miller" <davem at davemloft.net>
> Cc: Vineet Gupta <vgupta at synopsys.com>
> Cc: James Hogan <jhogan at kernel.org>
> Cc: Paul Burton <paul.burton at mips.com>
> Cc: Ralf Baechle <ralf at linux-mips.org>
> Cc: Kirill A. Shutemov <kirill at shutemov.name>
> Cc: Gerald Schaefer <gerald.schaefer at de.ibm.com>
> Cc: Christophe Leroy <christophe.leroy at c-s.fr>
> Cc: Ingo Molnar <mingo at kernel.org>
> Cc: linux-snps-arc at lists.infradead.org
> Cc: linux-mips at vger.kernel.org
> Cc: linux-arm-kernel at lists.infradead.org
> Cc: linux-ia64 at vger.kernel.org
> Cc: linuxppc-dev at lists.ozlabs.org
> Cc: linux-s390 at vger.kernel.org
> Cc: linux-sh at vger.kernel.org
> Cc: sparclinux at vger.kernel.org
> Cc: x86 at kernel.org
> Cc: linux-kernel at vger.kernel.org
> 
> Tested-by: Christophe Leroy <christophe.leroy at c-s.fr>		#PPC32
> Suggested-by: Catalin Marinas <catalin.marinas at arm.com>
> Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
> Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>
> Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
> ---
> 
> 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@arrakis.emea.arm.com/
> 
> Needs to be applied on linux-next (next-20191025).
> 
> Changes in V8:
> 
> - Enabled ARCH_HAS_DEBUG_VM_PGTABLE on PPC32 platform per Christophe
> - Updated feature documentation as DEBUG_VM_PGTABLE is now enabled on PPC32 platform
> - Moved ARCH_HAS_DEBUG_VM_PGTABLE earlier to indent it with DEBUG_VM per Christophe
> - Added an information message in debug_vm_pgtable() per Christophe
> - Dropped random_vaddr boundary condition checks per Christophe and Qian
> - Replaced virt_addr_valid() check with pfn_valid() check in debug_vm_pgtable()
> - Slightly changed pr_fmt(fmt) information
Hello Andrew,

Just wondering if this version looks okay or is there anything else which still
needs to be accommodated here first, before this test can be considered for merging ?
Thank you.

- Anshuman