Re: [PATCH v1 2/8] powerpc: hugetlb: Convert set_huge_pte_at() to take vma

Ryan Roberts
2023-09-22T08:41:10Z

On 22/09/2023 09:10, Christophe Leroy wrote:
>
>
> Le 22/09/2023 à 09:33, Ryan Roberts a écrit :
>> On 22/09/2023 07:56, Christophe Leroy wrote:
>>>
>>>
>>> Le 21/09/2023 à 18:20, Ryan Roberts a écrit :
>>>> In order to fix a bug, arm64 needs access to the vma inside it's
>>>> implementation of set_huge_pte_at(). Provide for this by converting the
>>>> mm parameter to be a vma. Any implementations that require the mm can
>>>> access it via vma->vm_mm.
>>>>
>>>> This commit makes the required powerpc modifications. Separate commits
>>>> update the other arches and core code, before the actual bug is fixed in
>>>> arm64.
>>>>
>>>> No behavioral changes intended.
>>>>
>>>> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
>>>> ---
>>>> arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h | 3 ++-
>>>> arch/powerpc/mm/book3s64/hugetlbpage.c | 2 +-
>>>> arch/powerpc/mm/book3s64/radix_hugetlbpage.c | 2 +-
>>>> arch/powerpc/mm/nohash/8xx.c | 2 +-
>>>> arch/powerpc/mm/pgtable.c | 7 ++++++-
>>>> 5 files changed, 11 insertions(+), 5 deletions(-)
>>>>
>>>> diff --git a/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h b/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
>>>> index de092b04ee1a..fff8cd726bc7 100644
>>>> --- a/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
>>>> +++ b/arch/powerpc/include/asm/nohash/32/hugetlb-8xx.h
>>>> @@ -46,7 +46,8 @@ static inline int check_and_get_huge_psize(int shift)
>>>> }
>>>>
>>>> #define __HAVE_ARCH_HUGE_SET_HUGE_PTE_AT
>>>> -void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte);
>>>> +void set_huge_pte_at(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t pte);
>>>> +void __set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte);
>>>
>>> Don't add the burden of an additional function, see below
>>>
>>>>
>>>> #define __HAVE_ARCH_HUGE_PTE_CLEAR
>>>> static inline void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
>>>> diff --git a/arch/powerpc/mm/book3s64/hugetlbpage.c b/arch/powerpc/mm/book3s64/hugetlbpage.c
>>>> index 3bc0eb21b2a0..ae7fd7c90eb8 100644
>>>> --- a/arch/powerpc/mm/book3s64/hugetlbpage.c
>>>> +++ b/arch/powerpc/mm/book3s64/hugetlbpage.c
>>>> @@ -147,7 +147,7 @@ void huge_ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr
>>>> if (radix_enabled())
>>>> return radix__huge_ptep_modify_prot_commit(vma, addr, ptep,
>>>> old_pte, pte);
>>>> - set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
>>>> + set_huge_pte_at(vma, addr, ptep, pte);
>>>> }
>>>>
>>>> void __init hugetlbpage_init_defaultsize(void)
>>>> diff --git a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>>>> index 17075c78d4bc..7cd40a334c3a 100644
>>>> --- a/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>>>> +++ b/arch/powerpc/mm/book3s64/radix_hugetlbpage.c
>>>> @@ -58,5 +58,5 @@ void radix__huge_ptep_modify_prot_commit(struct vm_area_struct *vma,
>>>> atomic_read(&mm->context.copros) > 0)
>>>> radix__flush_hugetlb_page(vma, addr);
>>>>
>>>> - set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
>>>> + set_huge_pte_at(vma, addr, ptep, pte);
>>>> }
>>>> diff --git a/arch/powerpc/mm/nohash/8xx.c b/arch/powerpc/mm/nohash/8xx.c
>>>> index dbbfe897455d..650a7a8496b6 100644
>>>> --- a/arch/powerpc/mm/nohash/8xx.c
>>>> +++ b/arch/powerpc/mm/nohash/8xx.c
>>>> @@ -91,7 +91,7 @@ static int __ref __early_map_kernel_hugepage(unsigned long va, phys_addr_t pa,
>>>> if (new && WARN_ON(pte_present(*ptep) && pgprot_val(prot)))
>>>> return -EINVAL;
>>>>
>>>> - set_huge_pte_at(&init_mm, va, ptep, pte_mkhuge(pfn_pte(pa >> PAGE_SHIFT, prot)));
>>>> + __set_huge_pte_at(&init_mm, va, ptep, pte_mkhuge(pfn_pte(pa >> PAGE_SHIFT, prot)));
>>>
>>> Call set_huge_pte_at() with a NULL vma instead.
>>
>> I'm happy to take your proposed approach if that's your preference. Another
>> option is to use a dummy VMA, as I have done in the core code, for the one call
>> site that calls set_huge_pte_at() with init_mm:
>>
>> struct vm_area_struct vma = TLB_FLUSH_VMA(&init_mm, 0);
>>
>> This is an existing macro that creates a dummy vma with vma->vm_mm filled in.
>> Then I pass &vma to the function.
>
> I don't like that, I prefer the solution I proposed. We already have a
> couple places where powerpc do things based on whether vma is NULL or not.
>
>>
>> Or yet another option would be to keep the mm param as is in set_huge_pte_at(),
>> and add a size param to the function. But then all call sites have the burden of
>> figuring out the size of the huge pte (although I think most know already).
>
> Indeed.
>
> arch_make_huge_pte() used to take a vma until commit 79c1c594f49a
> ("mm/hugetlb: change parameters of arch_make_huge_pte()").
>
> Should we try and have the same approach ? Or is it irrelevant ?

See [1]; I'm going to rework to pass mm + size parameter since the current
approach will break riscv.

[1]
https://lore.kernel.org/linux-arm-kernel/fc85f58e-e8ed-4b24-a3e5-d6288156595e@arm.com/

>
> Christophe
>
>>
>> Thanks,
>> Ryan
>>
>>>
>>>>
>>>> return 0;
>>>> }
>>>> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
>>>> index 3f86fd217690..9cbcb561a4d8 100644
>>>> --- a/arch/powerpc/mm/pgtable.c
>>>> +++ b/arch/powerpc/mm/pgtable.c
>>>> @@ -288,7 +288,7 @@ int huge_ptep_set_access_flags(struct vm_area_struct *vma,
>>>> }
>>>>
>>>> #if defined(CONFIG_PPC_8xx)
>>>> -void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte)
>>>> +void __set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte)
>>>
>>> Keep it as set_huge_pte_at() with vma argument.
>>>
>>>> {
>>>> pmd_t *pmd = pmd_off(mm, addr);
>>>
>>> Change to:
>>>
>>> pmd_t *pmd = vma ? pmd_off(vma->vm_mm, addr) : pmd_off_k(addr);
>>>
>>>> pte_basic_t val;
>>>> @@ -310,6 +310,11 @@ void set_huge_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_
>>>> for (i = 0; i < num; i++, entry++, val += SZ_4K)
>>>> *entry = val;
>>>> }
>>>> +
>>>> +void set_huge_pte_at(struct vm_area_struct *vma, unsigned long addr, pte_t *ptep, pte_t pte)
>>>> +{
>>>> + __set_huge_pte_at(vma->vm_mm, addr, ptep, pte);
>>>> +}
>>>
>>> Remove this burden.
>>>
>>>> #endif
>>>> #endif /* CONFIG_HUGETLB_PAGE */
>>>>
>>>
>>>
>>> Christophe
>>