Re: [PATCH] mm/debug_vm_pgtable: Ensure THP availability via has_transparent_hugepage()

[Christophe Leroy <christophe.leroy@xxxxxxxxxx>]

Le 18/05/2021 à 10:13, Anshuman Khandual a écrit :
> On certain platforms, THP support could not just be validated via the build
> option CONFIG_TRANSPARENT_HUGEPAGE. Instead has_transparent_hugepage() also
> needs to be called upon to verify THP runtime support. Otherwise the debug
> test might just run into unusable THP helpers like in the case of a 4K hash

s/might/will/

> config on powerpc platform [1]. This just moves all pfn_pmd() and pfn_pud()
> after THP runtime validation with has_transparent_hugepage() which prevents
> the mentioned problem.
>
> [1] https://bugzilla.kernel.org/show_bug.cgi?id=213069
>
> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>

There should be a Fixes:  tag

> ---
> This applies on v5.13-rc2 after the following patches.
>
> [1] https://lore.kernel.org/linux-mm/20210419071820.750217-1-liushixin2@xxxxxxxxxx/
> [2] https://lore.kernel.org/linux-mm/20210419071820.750217-2-liushixin2@xxxxxxxxxx/

I can't see any fixes: tag in those patches, and their subject line even targets them to -next. Are 
they meant to go to 5.13 and stable ?

If not, how do you coordinate between your patch that must go in 5.13 and in stable, and those two 
patches ? Shouldn't your patch go first and those other patches be rebased on top ?

>   mm/debug_vm_pgtable.c | 58 +++++++++++++++++++++++++++++++++++--------
>   1 file changed, 48 insertions(+), 10 deletions(-)
>
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index e2f35db8ba69..6ff92c8b0a00 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -146,13 +146,14 @@ static void __init pte_savedwrite_tests(unsigned long pfn, pgprot_t prot)
>   static void __init pmd_basic_tests(unsigned long pfn, int idx)
>   {
>   	pgprot_t prot = protection_map[idx];
> -	pmd_t pmd = pfn_pmd(pfn, prot);
>   	unsigned long val = idx, *ptr = &val;
> +	pmd_t pmd;
>   
>   	if (!has_transparent_hugepage())
>   		return;
>   
>   	pr_debug("Validating PMD basic (%pGv)\n", ptr);
> +	pmd = pfn_pmd(pfn, prot);
>   
>   	/*
>   	 * This test needs to be executed after the given page table entry
> @@ -232,9 +233,14 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
>   
>   static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pfn_pmd(pfn, prot);
> +	pmd_t pmd;
> +
> +	if (!has_transparent_hugepage())
> +		return;
>   
>   	pr_debug("Validating PMD leaf\n");
> +	pmd = pfn_pmd(pfn, prot);
> +
>   	/*
>   	 * PMD based THP is a leaf entry.
>   	 */
> @@ -244,12 +250,16 @@ static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)
>   
>   static void __init pmd_savedwrite_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pfn_pmd(pfn, prot);
> +	pmd_t pmd;
>   
>   	if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
>   		return;
>   
> +	if (!has_transparent_hugepage())
> +		return;
> +
>   	pr_debug("Validating PMD saved write\n");
> +	pmd = pfn_pmd(pfn, prot);
>   	WARN_ON(!pmd_savedwrite(pmd_mk_savedwrite(pmd_clear_savedwrite(pmd))));
>   	WARN_ON(pmd_savedwrite(pmd_clear_savedwrite(pmd_mk_savedwrite(pmd))));
>   }
> @@ -258,13 +268,14 @@ static void __init pmd_savedwrite_tests(unsigned long pfn, pgprot_t prot)
>   static void __init pud_basic_tests(struct mm_struct *mm, unsigned long pfn, int idx)
>   {
>   	pgprot_t prot = protection_map[idx];
> -	pud_t pud = pfn_pud(pfn, prot);
>   	unsigned long val = idx, *ptr = &val;
> +	pud_t pud;
>   
>   	if (!has_transparent_hugepage())
>   		return;
>   
>   	pr_debug("Validating PUD basic (%pGv)\n", ptr);
> +	pud = pfn_pud(pfn, prot);
>   
>   	/*
>   	 * This test needs to be executed after the given page table entry
> @@ -348,9 +359,13 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
>   
>   static void __init pud_leaf_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pud_t pud = pfn_pud(pfn, prot);
> +	pud_t pud;
> +
> +	if (!has_transparent_hugepage())
> +		return;
>   
>   	pr_debug("Validating PUD leaf\n");
> +	pud = pfn_pud(pfn, prot);
>   	/*
>   	 * PUD based THP is a leaf entry.
>   	 */
> @@ -642,12 +657,16 @@ static void __init pte_protnone_tests(unsigned long pfn, pgprot_t prot)
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   static void __init pmd_protnone_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
> +	pmd_t pmd;
>   
>   	if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
>   		return;
>   
> +	if (!has_transparent_hugepage())
> +		return;
> +
>   	pr_debug("Validating PMD protnone\n");
> +	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
>   	WARN_ON(!pmd_protnone(pmd));
>   	WARN_ON(!pmd_present(pmd));
>   }
> @@ -667,18 +686,26 @@ static void __init pte_devmap_tests(unsigned long pfn, pgprot_t prot)
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   static void __init pmd_devmap_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pfn_pmd(pfn, prot);
> +	pmd_t pmd;
> +
> +	if (!has_transparent_hugepage())
> +		return;
>   
>   	pr_debug("Validating PMD devmap\n");
> +	pmd = pfn_pmd(pfn, prot);
>   	WARN_ON(!pmd_devmap(pmd_mkdevmap(pmd)));
>   }
>   
>   #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
>   static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pud_t pud = pfn_pud(pfn, prot);
> +	pud_t pud;
> +
> +	if (!has_transparent_hugepage())
> +		return;
>   
>   	pr_debug("Validating PUD devmap\n");
> +	pud = pfn_pud(pfn, prot);
>   	WARN_ON(!pud_devmap(pud_mkdevmap(pud)));
>   }
>   #else  /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
> @@ -721,25 +748,33 @@ static void __init pte_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>   static void __init pmd_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pfn_pmd(pfn, prot);
> +	pmd_t pmd;
>   
>   	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
>   		return;
>   
> +	if (!has_transparent_hugepage())
> +		return;
> +
>   	pr_debug("Validating PMD soft dirty\n");
> +	pmd = pfn_pmd(pfn, prot);
>   	WARN_ON(!pmd_soft_dirty(pmd_mksoft_dirty(pmd)));
>   	WARN_ON(pmd_soft_dirty(pmd_clear_soft_dirty(pmd)));
>   }
>   
>   static void __init pmd_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
>   {
> -	pmd_t pmd = pfn_pmd(pfn, prot);
> +	pmd_t pmd;
>   
>   	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) ||
>   		!IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
>   		return;
>   
> +	if (!has_transparent_hugepage())
> +		return;
> +
>   	pr_debug("Validating PMD swap soft dirty\n");
> +	pmd = pfn_pmd(pfn, prot);
>   	WARN_ON(!pmd_swp_soft_dirty(pmd_swp_mksoft_dirty(pmd)));
>   	WARN_ON(pmd_swp_soft_dirty(pmd_swp_clear_soft_dirty(pmd)));
>   }
> @@ -768,6 +803,9 @@ static void __init pmd_swap_tests(unsigned long pfn, pgprot_t prot)
>   	swp_entry_t swp;
>   	pmd_t pmd;
>   
> +	if (!has_transparent_hugepage())
> +		return;
> +
>   	pr_debug("Validating PMD swap\n");
>   	pmd = pfn_pmd(pfn, prot);
>   	swp = __pmd_to_swp_entry(pmd);