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From: Anshuman Khandual <anshuman.khandual@arm.com>
Subject: Re: [PATCH 16/16] debug_vm_pgtable/ppc64: Add a variant of pfn_pte/pmd
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>, linux-mm@kvack.org,
 akpm@linux-foundation.org
References: <20200812063358.369514-1-aneesh.kumar@linux.ibm.com>
 <20200812063358.369514-16-aneesh.kumar@linux.ibm.com>
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Date: Thu, 13 Aug 2020 11:00:56 +0530
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On 08/12/2020 12:03 PM, Aneesh Kumar K.V wrote:
> The tests do expect _PAGE_PTE bit set by different page table accessors.
> This is not true for the kernel. Within the kernel, _PAGE_PTE bits are
> usually set by set_pte_at(). To make the below tests work correctly add test
> specific pfn_pte/pmd helpers that set _PAGE_PTE bit.
> 
> pte_t pte = pfn_pte(pfn, prot);
> WARN_ON(!pte_devmap(pte_mkdevmap(pte)));
> WARN_ON(!pte_savedwrite(pte_mk_savedwrite(pte_clear_savedwrite(pte))));
> 
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  mm/debug_vm_pgtable.c | 65 +++++++++++++++++++++++++++----------------
>  1 file changed, 41 insertions(+), 24 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index eea62d5e503b..153c925b5273 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -31,6 +31,23 @@
>  #include <asm/pgalloc.h>
>  #include <asm/tlbflush.h>
>  
> +#ifdef CONFIG_PPC_BOOK3S_64
> +static inline pte_t debug_vm_pfn_pte(unsigned long pfn, pgprot_t pgprot)
> +{
> +	pte_t pte = pfn_pte(pfn, pgprot);
> +	return __pte(pte_val(pte) | _PAGE_PTE);
> +
> +}
> +static inline pmd_t debug_vm_pfn_pmd(unsigned long pfn, pgprot_t pgprot)
> +{
> +	pmd_t pmd = pfn_pmd(pfn, pgprot);
> +	return __pmd(pmd_val(pmd) | _PAGE_PTE);
> +}
> +#else
> +#define debug_vm_pfn_pte(pfn, pgprot) pfn_pte(pfn, pgprot)
> +#define debug_vm_pfn_pmd(pfn, pgprot) pfn_pmd(pfn, pgprot)
> +#endif

Again, no platform specific constructs please. This defeats the whole purpose of
this test. If __PAGE_PTE is required for the helpers, then pfn_pmd/pte() could
be modified to accommodate that. We dont see similar issues on other platforms,
hence could you please explain why ppc64 is different here.