Re: [PATCH 5/9] x86/clear_pages: add clear_pages()

Peter Zijlstra
2023-04-06T08:23:29Z

On Sun, Apr 02, 2023 at 10:22:29PM -0700, Ankur Arora wrote:
> Add clear_pages() and define the ancillary clear_user_pages().
>
> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
> ---
> arch/x86/include/asm/page.h | 6 ++++++
> arch/x86/include/asm/page_32.h | 6 ++++++
> arch/x86/include/asm/page_64.h | 9 +++++++--
> 3 files changed, 19 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
> index d18e5c332cb9..03e3c69fc427 100644
> --- a/arch/x86/include/asm/page.h
> +++ b/arch/x86/include/asm/page.h
> @@ -28,6 +28,12 @@ static inline void clear_user_page(void *page, unsigned long vaddr,
> clear_page(page);
> }
>
> +static inline void clear_user_pages(void *page, unsigned long vaddr,
> + struct page *pg, unsigned int nsubpages)
> +{
> + clear_pages(page, nsubpages);
> +}

This seems dodgy, clear_user* has slightly different semantics. It needs
the access_ok() and stac/clac thing on at the very least.

> +
> static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
> struct page *topage)
> {
> diff --git a/arch/x86/include/asm/page_32.h b/arch/x86/include/asm/page_32.h
> index 580d71aca65a..3523d1150cfc 100644
> --- a/arch/x86/include/asm/page_32.h
> +++ b/arch/x86/include/asm/page_32.h
> @@ -22,6 +22,12 @@ static inline void clear_page(void *page)
> memset(page, 0, PAGE_SIZE);
> }
>
> +static inline void clear_pages(void *page, unsigned int nsubpages)
> +{
> + for (int i = 0; i < nsubpages; i++)
> + clear_page(page + i * PAGE_SIZE);

cond_resched() ?

> +}
> +
> static inline void copy_page(void *to, void *from)
> {
> memcpy(to, from, PAGE_SIZE);