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Message-ID: <af1a4992-bb4b-bd91-6ff9-0783ef7528ae@arm.com>
Date: Thu, 9 Mar 2023 11:03:10 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>,
linux-mm@...ck.org, linux-arch@...r.kernel.org
Cc: linux-kernel@...r.kernel.org,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 08/34] arm64: Implement the new page table range API
On 28/02/2023 21:37, Matthew Wilcox (Oracle) wrote:
> Add set_ptes(), update_mmu_cache_range() and flush_dcache_folio().
> Change the PG_dcache_clean flag from being per-page to per-folio.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> ---
> arch/arm64/include/asm/cacheflush.h | 4 +++-
> arch/arm64/include/asm/pgtable.h | 25 ++++++++++++++------
> arch/arm64/mm/flush.c | 36 +++++++++++------------------
> 3 files changed, 35 insertions(+), 30 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> index 37185e978aeb..d115451ed263 100644
> --- a/arch/arm64/include/asm/cacheflush.h
> +++ b/arch/arm64/include/asm/cacheflush.h
> @@ -114,7 +114,7 @@ extern void copy_to_user_page(struct vm_area_struct *, struct page *,
> #define copy_to_user_page copy_to_user_page
>
> /*
> - * flush_dcache_page is used when the kernel has written to the page
> + * flush_dcache_folio is used when the kernel has written to the page
> * cache page at virtual address page->virtual.
> *
> * If this page isn't mapped (ie, page_mapping == NULL), or it might
> @@ -127,6 +127,8 @@ extern void copy_to_user_page(struct vm_area_struct *, struct page *,
> */
> #define ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE 1
> extern void flush_dcache_page(struct page *);
> +void flush_dcache_folio(struct folio *);
> +#define flush_dcache_folio flush_dcache_folio
>
> static __always_inline void icache_inval_all_pou(void)
> {
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 69765dc697af..4d1b79dbff16 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -355,12 +355,21 @@ static inline void __set_pte_at(struct mm_struct *mm, unsigned long addr,
> set_pte(ptep, pte);
> }
>
> -static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
> - pte_t *ptep, pte_t pte)
> -{
> - page_table_check_ptes_set(mm, addr, ptep, pte, 1);
> - return __set_pte_at(mm, addr, ptep, pte);
> +static inline void set_ptes(struct mm_struct *mm, unsigned long addr,
> + pte_t *ptep, pte_t pte, unsigned int nr)
> +{
> + page_table_check_ptes_set(mm, addr, ptep, pte, nr);
> +
> + for (;;) {
> + __set_pte_at(mm, addr, ptep, pte);
> + if (--nr == 0)
> + break;
> + ptep++;
> + addr += PAGE_SIZE;
> + pte_val(pte) += PAGE_SIZE;
For systems that support > 48-bit PA, arm64 places high bits [51:48] of the PA
at a low position in the PTE. I think I've convinced myself that this is ok
though, because set_ptes() promises that the range is always within a single PMD
and therefore its guaranteed that we will not have ptes straddling both sides of
the 48 bit boundary for a single call?
Also, its not clear to me if set_ptes() could be called for a range of
not-present ptes? (i.e. clearing the pte-range or swap entries, etc). If so,
then I guess you would only want to increment the address if pte_present(pte)?
I'm guessing that batch-clearing ptes might appear in the near future so might
be sensible to support that now?
Regardless, a comment to make these assumptions clear would be useful.
Thanks,
Ryan
> + }
> }
> +#define set_pte_at(mm, addr, ptep, pte) set_ptes(mm, addr, ptep, pte, 1)
>
> /*
> * Huge pte definitions.
> @@ -1059,8 +1068,8 @@ static inline void arch_swap_restore(swp_entry_t entry, struct folio *folio)
> /*
> * On AArch64, the cache coherency is handled via the set_pte_at() function.
> */
> -static inline void update_mmu_cache(struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep)
> +static inline void update_mmu_cache_range(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep, unsigned int nr)
> {
> /*
> * We don't do anything here, so there's a very small chance of
> @@ -1069,6 +1078,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
> */
> }
>
> +#define update_mmu_cache(vma, addr, ptep) \
> + update_mmu_cache_range(vma, addr, ptep, 1)
> #define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
>
> #ifdef CONFIG_ARM64_PA_BITS_52
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index 5f9379b3c8c8..deb781af0a3a 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -50,20 +50,13 @@ void copy_to_user_page(struct vm_area_struct *vma, struct page *page,
>
> void __sync_icache_dcache(pte_t pte)
> {
> - struct page *page = pte_page(pte);
> + struct folio *folio = page_folio(pte_page(pte));
>
> - /*
> - * HugeTLB pages are always fully mapped, so only setting head page's
> - * PG_dcache_clean flag is enough.
> - */
> - if (PageHuge(page))
> - page = compound_head(page);
> -
> - if (!test_bit(PG_dcache_clean, &page->flags)) {
> - sync_icache_aliases((unsigned long)page_address(page),
> - (unsigned long)page_address(page) +
> - page_size(page));
> - set_bit(PG_dcache_clean, &page->flags);
> + if (!test_bit(PG_dcache_clean, &folio->flags)) {
> + sync_icache_aliases((unsigned long)folio_address(folio),
> + (unsigned long)folio_address(folio) +
> + folio_size(folio));
> + set_bit(PG_dcache_clean, &folio->flags);
> }
> }
> EXPORT_SYMBOL_GPL(__sync_icache_dcache);
> @@ -73,17 +66,16 @@ EXPORT_SYMBOL_GPL(__sync_icache_dcache);
> * it as dirty for later flushing when mapped in user space (if executable,
> * see __sync_icache_dcache).
> */
> -void flush_dcache_page(struct page *page)
> +void flush_dcache_folio(struct folio *folio)
> {
> - /*
> - * HugeTLB pages are always fully mapped and only head page will be
> - * set PG_dcache_clean (see comments in __sync_icache_dcache()).
> - */
> - if (PageHuge(page))
> - page = compound_head(page);
> + if (test_bit(PG_dcache_clean, &folio->flags))
> + clear_bit(PG_dcache_clean, &folio->flags);
> +}
> +EXPORT_SYMBOL(flush_dcache_folio);
>
> - if (test_bit(PG_dcache_clean, &page->flags))
> - clear_bit(PG_dcache_clean, &page->flags);
> +void flush_dcache_page(struct page *page)
> +{
> + flush_dcache_folio(page_folio(page));
> }
> EXPORT_SYMBOL(flush_dcache_page);
>
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