[PATCH V5 1/4] mm/debug_vm_pgtable: Add tests validating arch helpers for core MM features

[Anshuman Khandual]

On 07/16/2020 07:44 PM, Steven Price wrote:
> On 13/07/2020 04:23, Anshuman Khandual wrote:
>> This adds new tests validating arch page table helpers for these following
>> core memory features. These tests create and test specific mapping types at
>> various page table levels.
>>
>> 1. SPECIAL mapping
>> 2. PROTNONE mapping
>> 3. DEVMAP mapping
>> 4. SOFTDIRTY mapping
>> 5. SWAP mapping
>> 6. MIGRATION mapping
>> 7. HUGETLB mapping
>> 8. THP mapping
>>
>> Cc: Andrew Morton <akpm at linux-foundation.org>
>> Cc: Gerald Schaefer <gerald.schaefer at de.ibm.com>
>> Cc: Christophe Leroy <christophe.leroy at c-s.fr>
>> Cc: Mike Rapoport <rppt at linux.ibm.com>
>> Cc: Vineet Gupta <vgupta at synopsys.com>
>> Cc: Catalin Marinas <catalin.marinas at arm.com>
>> Cc: Will Deacon <will at kernel.org>
>> Cc: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>> Cc: Paul Mackerras <paulus at samba.org>
>> Cc: Michael Ellerman <mpe at ellerman.id.au>
>> Cc: Heiko Carstens <heiko.carstens at de.ibm.com>
>> Cc: Vasily Gorbik <gor at linux.ibm.com>
>> Cc: Christian Borntraeger <borntraeger at de.ibm.com>
>> Cc: Thomas Gleixner <tglx at linutronix.de>
>> Cc: Ingo Molnar <mingo at redhat.com>
>> Cc: Borislav Petkov <bp at alien8.de>
>> Cc: "H. Peter Anvin" <hpa at zytor.com>
>> Cc: Kirill A. Shutemov <kirill at shutemov.name>
>> Cc: Paul Walmsley <paul.walmsley at sifive.com>
>> Cc: Palmer Dabbelt <palmer at dabbelt.com>
>> Cc: linux-snps-arc at lists.infradead.org
>> Cc: linux-arm-kernel at lists.infradead.org
>> Cc: linuxppc-dev at lists.ozlabs.org
>> Cc: linux-s390 at vger.kernel.org
>> Cc: linux-riscv at lists.infradead.org
>> Cc: x86 at kernel.org
>> Cc: linux-mm at kvack.org
>> Cc: linux-arch at vger.kernel.org
>> Cc: linux-kernel at vger.kernel.org
>> Tested-by: Vineet Gupta <vgupta at synopsys.com>    #arc
>> Reviewed-by: Zi Yan <ziy at nvidia.com>
>> Suggested-by: Catalin Marinas <catalin.marinas at arm.com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
>> ---
>>   mm/debug_vm_pgtable.c | 302 +++++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 301 insertions(+), 1 deletion(-)
>>
>> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
>> index 61ab16fb2e36..2fac47db3eb7 100644
>> --- a/mm/debug_vm_pgtable.c
>> +++ b/mm/debug_vm_pgtable.c
> [...]
>> +
>> +static void __init pte_swap_tests(unsigned long pfn, pgprot_t prot)
>> +{
>> +    swp_entry_t swp;
>> +    pte_t pte;
>> +
>> +    pte = pfn_pte(pfn, prot);
>> +    swp = __pte_to_swp_entry(pte);
> 
> Minor issue: this doesn't look necessarily valid - there's no reason a normal PTE can be turned into a swp_entry. In practise this is likely to work on all architectures because there's no reason not to use (at least) all the PFN bits for the swap entry, but it doesn't exactly seem correct.

Agreed, that it is a simple test but nonetheless a valid one which
makes sure that PFN value remained unchanged during pte <---> swp
conversion.

> 
> Can we start with a swp_entry_t (from __swp_entry()) and check the round trip of that?
> 
> It would also seem sensible to have a check that is_swap_pte(__swp_entry_to_pte(__swp_entry(x,y))) is true.

>From past experiences, getting any these new tests involving platform
helpers, working on all existing enabled archs is neither trivial nor
going to be quick. Existing tests here are known to succeed in enabled
platforms. Nonetheless, proposed tests as in the above suggestions do
make sense but will try to accommodate them in a later patch.