Re: [PATCH v10 11/12] powerpc: mm: Use set_pte_at_unchecked() for early-boot / internal usages

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 13/03/2024 à 05:21, Rohan McLure a écrit :
> In the new set_ptes() API, set_pte_at() (a special case of set_ptes())
> is intended to be instrumented by the page table check facility. There
> are however several other routines that constitute the API for setting
> page table entries, including set_pmd_at() among others. Such routines
> are themselves implemented in terms of set_ptes_at().
> 
> A future patch providing support for page table checking on powerpc
> must take care to avoid duplicate calls to
> page_table_check_p{te,md,ud}_set(). Allow for assignment of pte entries
> without instrumentation through the set_pte_at_unchecked() routine
> introduced in this patch.
> 
> Cause API-facing routines that call set_pte_at() to instead call
> set_pte_at_unchecked(), which will remain uninstrumented by page
> table check. set_ptes() is itself implemented by calls to
> __set_pte_at(), so this eliminates redundant code.
> 
> Also prefer set_pte_at_unchecked() in early-boot usages which should not be
> instrumented.
> 
> Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
> ---
> v9: New patch
> v10: don't reuse __set_pte_at(), as that will not apply filters. Instead
> use new set_pte_at_unchecked().

Are filters needed at all in those usecases ?

> ---
>   arch/powerpc/include/asm/pgtable.h       | 2 ++
>   arch/powerpc/mm/book3s64/hash_pgtable.c  | 2 +-
>   arch/powerpc/mm/book3s64/pgtable.c       | 6 +++---
>   arch/powerpc/mm/book3s64/radix_pgtable.c | 8 ++++----
>   arch/powerpc/mm/nohash/book3e_pgtable.c  | 2 +-
>   arch/powerpc/mm/pgtable.c                | 7 +++++++
>   arch/powerpc/mm/pgtable_32.c             | 2 +-
>   7 files changed, 19 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 3741a63fb82e..6ff1d8cfa216 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -44,6 +44,8 @@ struct mm_struct;
>   void set_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
>   		pte_t pte, unsigned int nr);
>   #define set_ptes set_ptes
> +void set_pte_at_unchecked(struct mm_struct *mm, unsigned long addr,
> +			  pte_t *ptep, pte_t pte);
>   #define update_mmu_cache(vma, addr, ptep) \
>   	update_mmu_cache_range(NULL, vma, addr, ptep, 1)
>   
> diff --git a/arch/powerpc/mm/book3s64/hash_pgtable.c b/arch/powerpc/mm/book3s64/hash_pgtable.c
> index 988948d69bc1..871472f99a01 100644
> --- a/arch/powerpc/mm/book3s64/hash_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/hash_pgtable.c
> @@ -165,7 +165,7 @@ int hash__map_kernel_page(unsigned long ea, unsigned long pa, pgprot_t prot)
>   		ptep = pte_alloc_kernel(pmdp, ea);
>   		if (!ptep)
>   			return -ENOMEM;
> -		set_pte_at(&init_mm, ea, ptep, pfn_pte(pa >> PAGE_SHIFT, prot));
> +		set_pte_at_unchecked(&init_mm, ea, ptep, pfn_pte(pa >> PAGE_SHIFT, prot));
>   	} else {
>   		/*
>   		 * If the mm subsystem is not fully up, we cannot create a
> diff --git a/arch/powerpc/mm/book3s64/pgtable.c b/arch/powerpc/mm/book3s64/pgtable.c
> index 3438ab72c346..25082ab6018b 100644
> --- a/arch/powerpc/mm/book3s64/pgtable.c
> +++ b/arch/powerpc/mm/book3s64/pgtable.c
> @@ -116,7 +116,7 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
>   	WARN_ON(!(pmd_large(pmd)));
>   #endif
>   	trace_hugepage_set_pmd(addr, pmd_val(pmd));
> -	return set_pte_at(mm, addr, pmdp_ptep(pmdp), pmd_pte(pmd));
> +	return set_pte_at_unchecked(mm, addr, pmdp_ptep(pmdp), pmd_pte(pmd));
>   }
>   
>   void set_pud_at(struct mm_struct *mm, unsigned long addr,
> @@ -133,7 +133,7 @@ void set_pud_at(struct mm_struct *mm, unsigned long addr,
>   	WARN_ON(!(pud_large(pud)));
>   #endif
>   	trace_hugepage_set_pud(addr, pud_val(pud));
> -	return set_pte_at(mm, addr, pudp_ptep(pudp), pud_pte(pud));
> +	return set_pte_at_unchecked(mm, addr, pudp_ptep(pudp), pud_pte(pud));
>   }
>   
>   static void do_serialize(void *arg)
> @@ -539,7 +539,7 @@ void ptep_modify_prot_commit(struct vm_area_struct *vma, unsigned long addr,
>   	if (radix_enabled())
>   		return radix__ptep_modify_prot_commit(vma, addr,
>   						      ptep, old_pte, pte);
> -	set_pte_at(vma->vm_mm, addr, ptep, pte);
> +	set_pte_at_unchecked(vma->vm_mm, addr, ptep, pte);
>   }
>   
>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index 46fa46ce6526..c661e42bb2f1 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -109,7 +109,7 @@ static int early_map_kernel_page(unsigned long ea, unsigned long pa,
>   	ptep = pte_offset_kernel(pmdp, ea);
>   
>   set_the_pte:
> -	set_pte_at(&init_mm, ea, ptep, pfn_pte(pfn, flags));
> +	set_pte_at_unchecked(&init_mm, ea, ptep, pfn_pte(pfn, flags));
>   	asm volatile("ptesync": : :"memory");
>   	return 0;
>   }
> @@ -1522,7 +1522,7 @@ void radix__ptep_modify_prot_commit(struct vm_area_struct *vma,
>   	    (atomic_read(&mm->context.copros) > 0))
>   		radix__flush_tlb_page(vma, addr);
>   
> -	set_pte_at(mm, addr, ptep, pte);
> +	set_pte_at_unchecked(mm, addr, ptep, pte);
>   }
>   
>   int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
> @@ -1533,7 +1533,7 @@ int pud_set_huge(pud_t *pud, phys_addr_t addr, pgprot_t prot)
>   	if (!radix_enabled())
>   		return 0;
>   
> -	set_pte_at(&init_mm, 0 /* radix unused */, ptep, new_pud);
> +	set_pte_at_unchecked(&init_mm, 0 /* radix unused */, ptep, new_pud);
>   
>   	return 1;
>   }
> @@ -1580,7 +1580,7 @@ int pmd_set_huge(pmd_t *pmd, phys_addr_t addr, pgprot_t prot)
>   	if (!radix_enabled())
>   		return 0;
>   
> -	set_pte_at(&init_mm, 0 /* radix unused */, ptep, new_pmd);
> +	set_pte_at_unchecked(&init_mm, 0 /* radix unused */, ptep, new_pmd);
>   
>   	return 1;
>   }
> diff --git a/arch/powerpc/mm/nohash/book3e_pgtable.c b/arch/powerpc/mm/nohash/book3e_pgtable.c
> index 1c5e4ecbebeb..10d487b2b991 100644
> --- a/arch/powerpc/mm/nohash/book3e_pgtable.c
> +++ b/arch/powerpc/mm/nohash/book3e_pgtable.c
> @@ -111,7 +111,7 @@ int __ref map_kernel_page(unsigned long ea, phys_addr_t pa, pgprot_t prot)
>   		}
>   		ptep = pte_offset_kernel(pmdp, ea);
>   	}
> -	set_pte_at(&init_mm, ea, ptep, pfn_pte(pa >> PAGE_SHIFT, prot));
> +	set_pte_at_unchecked(&init_mm, ea, ptep, pfn_pte(pa >> PAGE_SHIFT, prot));
>   
>   	smp_wmb();
>   	return 0;
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index e8e0289d7ab0..352679cf2684 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -227,6 +227,13 @@ void set_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
>   	}
>   }
>   
> +void set_pte_at_unchecked(struct mm_struct *mm, unsigned long addr,
> +			  pte_t *ptep, pte_t pte)
> +{

No need of the

VM_WARN_ON(pte_hw_valid(*ptep) && !pte_protnone(*ptep));

which is in set_ptes() ?

> +	pte = set_pte_filter(pte, addr);
> +	__set_pte_at(mm, addr, ptep, pte, 0);
> +}
> +
>   void unmap_kernel_page(unsigned long va)
>   {
>   	pmd_t *pmdp = pmd_off_k(va);
> diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> index 4be97b4a44f9..a5a26faf91ec 100644
> --- a/arch/powerpc/mm/pgtable_32.c
> +++ b/arch/powerpc/mm/pgtable_32.c
> @@ -89,7 +89,7 @@ int __ref map_kernel_page(unsigned long va, phys_addr_t pa, pgprot_t prot)
>   		 * hash table
>   		 */
>   		BUG_ON((pte_present(*pg) | pte_hashpte(*pg)) && pgprot_val(prot));
> -		set_pte_at(&init_mm, va, pg, pfn_pte(pa >> PAGE_SHIFT, prot));
> +		set_pte_at_unchecked(&init_mm, va, pg, pfn_pte(pa >> PAGE_SHIFT, prot));
>   	}
>   	smp_wmb();
>   	return err;