Re: [PATCH v2 1/3] arm64/mm: Refactor PMD_PRESENT_INVALID and PTE_PROT_NONE bits

Catalin Marinas
2024-04-29T16:20:34Z

On Mon, Apr 29, 2024 at 03:02:05PM +0100, Ryan Roberts wrote:
> diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
> index dd9ee67d1d87..de62e6881154 100644
> --- a/arch/arm64/include/asm/pgtable-prot.h
> +++ b/arch/arm64/include/asm/pgtable-prot.h
> @@ -18,14 +18,7 @@
> #define PTE_DIRTY (_AT(pteval_t, 1) << 55)
> #define PTE_SPECIAL (_AT(pteval_t, 1) << 56)
> #define PTE_DEVMAP (_AT(pteval_t, 1) << 57)
> -#define PTE_PROT_NONE (_AT(pteval_t, 1) << 58) /* only when !PTE_VALID */
> -
> -/*
> - * This bit indicates that the entry is present i.e. pmd_page()
> - * still points to a valid huge page in memory even if the pmd
> - * has been invalidated.
> - */
> -#define PMD_PRESENT_INVALID (_AT(pteval_t, 1) << 59) /* only when !PMD_SECT_VALID */
> +#define PTE_INVALID (_AT(pteval_t, 1) << 59) /* only when !PTE_VALID */

Nitpick - I prefer the PTE_PRESENT_INVALID name as it makes it clearer
it's a present pte. We already have PTE_VALID, calling it PTE_INVALID
looks like a negation only.

> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index afdd56d26ad7..8dd4637d6b56 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -105,7 +105,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
> /*
> * The following only work if pte_present(). Undefined behaviour otherwise.
> */
> -#define pte_present(pte) (!!(pte_val(pte) & (PTE_VALID | PTE_PROT_NONE)))
> +#define pte_present(pte) (pte_valid(pte) || pte_invalid(pte))
> #define pte_young(pte) (!!(pte_val(pte) & PTE_AF))
> #define pte_special(pte) (!!(pte_val(pte) & PTE_SPECIAL))
> #define pte_write(pte) (!!(pte_val(pte) & PTE_WRITE))
> @@ -132,6 +132,7 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
> #define pte_dirty(pte) (pte_sw_dirty(pte) || pte_hw_dirty(pte))
>
> #define pte_valid(pte) (!!(pte_val(pte) & PTE_VALID))
> +#define pte_invalid(pte) ((pte_val(pte) & (PTE_VALID | PTE_INVALID)) == PTE_INVALID)

Same argument as above, pte_invalid() looks confusing to me, better (to
me) as pte_present_invalid().

I think it's sufficient to check PTE_PRESENT_INVALID only. We'd never
have both bits set, so no need for mask and compare.

> /*
> * Execute-only user mappings do not have the PTE_USER bit set. All valid
> * kernel mappings have the PTE_UXN bit set.
> @@ -261,6 +262,13 @@ static inline pte_t pte_mkpresent(pte_t pte)
> return set_pte_bit(pte, __pgprot(PTE_VALID));
> }
>
> +static inline pte_t pte_mkinvalid(pte_t pte)
> +{
> + pte = set_pte_bit(pte, __pgprot(PTE_INVALID));
> + pte = clear_pte_bit(pte, __pgprot(PTE_VALID));
> + return pte;
> +}

I wonder whether we need to define this. I guess it makes sense than
having the pmd_mkinvalid() use the PTE_* definitions directly, though it
won't be something we need to do on a pte.

> +
> static inline pmd_t pmd_mkcont(pmd_t pmd)
> {
> return __pmd(pmd_val(pmd) | PMD_SECT_CONT);
> @@ -469,7 +477,7 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
> */
> static inline int pte_protnone(pte_t pte)
> {
> - return (pte_val(pte) & (PTE_VALID | PTE_PROT_NONE)) == PTE_PROT_NONE;
> + return pte_invalid(pte) && !pte_user(pte) && !pte_user_exec(pte);
> }
>
> static inline int pmd_protnone(pmd_t pmd)
> @@ -478,12 +486,7 @@ static inline int pmd_protnone(pmd_t pmd)
> }
> #endif
>
> -#define pmd_present_invalid(pmd) (!!(pmd_val(pmd) & PMD_PRESENT_INVALID))
> -
> -static inline int pmd_present(pmd_t pmd)
> -{
> - return pte_present(pmd_pte(pmd)) || pmd_present_invalid(pmd);
> -}
> +#define pmd_present(pmd) pte_present(pmd_pte(pmd))
>
> /*
> * THP definitions.
> @@ -508,14 +511,7 @@ static inline int pmd_trans_huge(pmd_t pmd)
> #define pmd_mkclean(pmd) pte_pmd(pte_mkclean(pmd_pte(pmd)))
> #define pmd_mkdirty(pmd) pte_pmd(pte_mkdirty(pmd_pte(pmd)))
> #define pmd_mkyoung(pmd) pte_pmd(pte_mkyoung(pmd_pte(pmd)))
> -
> -static inline pmd_t pmd_mkinvalid(pmd_t pmd)
> -{
> - pmd = set_pmd_bit(pmd, __pgprot(PMD_PRESENT_INVALID));
> - pmd = clear_pmd_bit(pmd, __pgprot(PMD_SECT_VALID));
> -
> - return pmd;
> -}
> +#define pmd_mkinvalid(pmd) pte_pmd(pte_mkinvalid(pmd_pte(pmd)))
>
> #define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd))
>
> @@ -1027,7 +1023,7 @@ static inline pte_t pte_modify(pte_t pte, pgprot_t newprot)
> * in MAIR_EL1. The mask below has to include PTE_ATTRINDX_MASK.
> */
> const pteval_t mask = PTE_USER | PTE_PXN | PTE_UXN | PTE_RDONLY |
> - PTE_PROT_NONE | PTE_VALID | PTE_WRITE | PTE_GP |
> + PTE_INVALID | PTE_VALID | PTE_WRITE | PTE_GP |
> PTE_ATTRINDX_MASK;
> /* preserve the hardware dirty information */
> if (pte_hw_dirty(pte))
> @@ -1076,17 +1072,17 @@ static inline int pgd_devmap(pgd_t pgd)
> #ifdef CONFIG_PAGE_TABLE_CHECK
> static inline bool pte_user_accessible_page(pte_t pte)
> {
> - return pte_present(pte) && (pte_user(pte) || pte_user_exec(pte));
> + return pte_valid(pte) && (pte_user(pte) || pte_user_exec(pte));
> }

This looks fine, it doesn't change the semantics since PROT_NONE never
had pte_user() or pte_user_exec().

> static inline bool pmd_user_accessible_page(pmd_t pmd)
> {
> - return pmd_leaf(pmd) && !pmd_present_invalid(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd));
> + return pmd_valid(pmd) && !pmd_table(pmd) && (pmd_user(pmd) || pmd_user_exec(pmd));
> }

Maybe our pmd_leaf() should actually check valid && !table instead of
present and no need to change these.

> static inline bool pud_user_accessible_page(pud_t pud)
> {
> - return pud_leaf(pud) && (pud_user(pud) || pud_user_exec(pud));
> + return pud_valid(pud) && !pud_table(pud) && (pud_user(pud) || pud_user_exec(pud));
> }
> #endif

Same here.

Otherwise I'm happy with the patch. Feel free to add:

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>

As for getting it into 6.10, I'd say it's pretty late. Are there other
dependencies on core kernel fixes?

--
Catalin