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

Christophe Leroy
2023-09-22T08:11:10Z

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 ?

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
>