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

[Ryan Roberts <ryan.roberts@arm.com>]

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.

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).

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