Re: [PATCH 2/5] arm64/mm: Replace PXD_TABLE_BIT with PXD_TYPE_[MASK|SECT]

[Ryan Roberts]

On 05/10/2024 13:38, Anshuman Khandual wrote:
> This modifies existing block mapping related helpers e.g [pmd|pud]_mkhuge()
> , mk_[pmd|pud]_sect_prot() and pmd_trans_huge() to use PXD_TYPE_[MASK|SECT]
> instead of corresponding PXD_TABLE_BIT. This also moves pmd_sect() earlier
> for the symbol's availability preventing a build warning.
> 
> While here this also drops pmd_val() check from pmd_trans_huge() helper, as
> pmd_present() returning true already ensures that pmd_val() cannot be false
> 
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Cc: Ryan Roberts <ryan.roberts@xxxxxxx>
> Cc: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---
>  arch/arm64/include/asm/pgtable.h | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index fa4c32a9f572..45c49c5ace80 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -484,12 +484,12 @@ static inline pmd_t pte_pmd(pte_t pte)
>  
>  static inline pgprot_t mk_pud_sect_prot(pgprot_t prot)
>  {
> -	return __pgprot((pgprot_val(prot) & ~PUD_TABLE_BIT) | PUD_TYPE_SECT);
> +	return __pgprot((pgprot_val(prot) & ~PUD_TYPE_MASK) | PUD_TYPE_SECT);
>  }
>  
>  static inline pgprot_t mk_pmd_sect_prot(pgprot_t prot)
>  {
> -	return __pgprot((pgprot_val(prot) & ~PMD_TABLE_BIT) | PMD_TYPE_SECT);
> +	return __pgprot((pgprot_val(prot) & ~PMD_TYPE_MASK) | PMD_TYPE_SECT);
>  }
>  
>  static inline pte_t pte_swp_mkexclusive(pte_t pte)
> @@ -554,10 +554,13 @@ static inline int pmd_protnone(pmd_t pmd)
>   * THP definitions.
>   */
>  
> +#define pmd_sect(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
> +				 PMD_TYPE_SECT)
> +
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  static inline int pmd_trans_huge(pmd_t pmd)
>  {
> -	return pmd_val(pmd) && pmd_present(pmd) && !(pmd_val(pmd) & PMD_TABLE_BIT);
> +	return pmd_present(pmd) && pmd_sect(pmd);

Bug? Prevously we would have returned true for a "present-invalid" PMD block
mapping - that's one which is formatted as a PMD block mapping except the
PTE_VALID bit is clear and PTE_PRESENT_INVALID is set. But now, due to
pmd_sect() testing VALID is set (via PMD_TYPE_SECT), we no longer return true in
this case.

>  }
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>  
> @@ -586,7 +589,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
>  
>  #define pmd_write(pmd)		pte_write(pmd_pte(pmd))
>  
> -#define pmd_mkhuge(pmd)		(__pmd(pmd_val(pmd) & ~PMD_TABLE_BIT))
> +#define pmd_mkhuge(pmd)		(__pmd((pmd_val(pmd) & ~PMD_TYPE_MASK) | PMD_TYPE_SECT))

I'm not sure if this also suffers from a similar problem? Is it possible that a
present-invalid pmd would be passed to pmd_mkhuge()? If so, then we are now
incorrectly setting the PTE_VALID bit.

>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  #define pmd_devmap(pmd)		pte_devmap(pmd_pte(pmd))
> @@ -614,7 +617,7 @@ static inline pmd_t pmd_mkspecial(pmd_t pmd)
>  #define pud_mkyoung(pud)	pte_pud(pte_mkyoung(pud_pte(pud)))
>  #define pud_write(pud)		pte_write(pud_pte(pud))
>  
> -#define pud_mkhuge(pud)		(__pud(pud_val(pud) & ~PUD_TABLE_BIT))
> +#define pud_mkhuge(pud)		(__pud((pud_val(pud) & ~PUD_TYPE_MASK) | PUD_TYPE_SECT))
>  
>  #define __pud_to_phys(pud)	__pte_to_phys(pud_pte(pud))
>  #define __phys_to_pud_val(phys)	__phys_to_pte_val(phys)
> @@ -712,8 +715,6 @@ extern pgprot_t phys_mem_access_prot(struct file *file, unsigned long pfn,
>  
>  #define pmd_table(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
>  				 PMD_TYPE_TABLE)
> -#define pmd_sect(pmd)		((pmd_val(pmd) & PMD_TYPE_MASK) == \
> -				 PMD_TYPE_SECT)
>  #define pmd_leaf(pmd)		(pmd_present(pmd) && !pmd_table(pmd))
>  #define pmd_bad(pmd)		(!pmd_table(pmd))
>