Re: [PATCH v1] arm64/mm: Make set_ptes() robust when OAs cross 48-bit boundary

Catalin Marinas
2024-01-25T17:07:48Z

On Tue, Jan 23, 2024 at 04:17:18PM +0000, Ryan Roberts wrote:
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 79ce70fbb751..734b39401a05 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -92,6 +92,14 @@ static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
> #define pfn_pte(pfn,prot) \
> __pte(__phys_to_pte_val((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot))
>
> +/*
> + * Select all bits except the pfn
> + */
> +static inline pgprot_t pte_pgprot(pte_t pte)
> +{
> + return __pgprot(pte_val(pte) & ~PTE_ADDR_MASK);
> +}
> +
> #define pte_none(pte) (!pte_val(pte))
> #define pte_clear(mm,addr,ptep) set_pte(ptep, __pte(0))
> #define pte_page(pte) (pfn_to_page(pte_pfn(pte)))
> @@ -341,6 +349,12 @@ static inline void __sync_cache_and_tags(pte_t pte, unsigned int nr_pages)
> mte_sync_tags(pte, nr_pages);
> }
>
> +#define pte_next_pfn pte_next_pfn
> +static inline pte_t pte_next_pfn(pte_t pte)
> +{
> + return pfn_pte(pte_pfn(pte) + 1, pte_pgprot(pte));
> +}

While I see why you wanted to optimise this, I'd rather keep the
pte_pgprot() change separate and at a later time. This will conflict
(fail to build) with Ard's patch removing PTE_ADDR_MASK:

https://lore.kernel.org/all/20240123145258.1462979-89-ardb+git@google.com/

This masking out is no longer straightforward with support for LPA2
(especially the 52-bit physical addresses with 4K pages): bits 8 and 9
of the PTE either contain bits 50, 51 of the PA or the shareability
attribute if FEAT_LPA2 is not present. In the latter case, we need them
preserved.

--
Catalin