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Date:   Fri, 7 Apr 2023 12:34:44 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Ankur Arora <ankur.a.arora@oracle.com>
Cc:     linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org,
        torvalds@linux-foundation.org, akpm@linux-foundation.org,
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        bharata@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com
Subject: Re: [PATCH 5/9] x86/clear_pages: add clear_pages()
Message-ID: <20230407103444.GB430894@hirez.programming.kicks-ass.net>
References: <20230403052233.1880567-1-ankur.a.arora@oracle.com>
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 <20230406082304.GE386572@hirez.programming.kicks-ass.net>
 <878rf4jz1x.fsf@oracle.com>
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On Thu, Apr 06, 2023 at 05:50:18PM -0700, Ankur Arora wrote:
> 
> Peter Zijlstra <peterz@infradead.org> writes:
> 
> > 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.
> 
> That can't be right. On x86, clear_user_page(), copy_user_page() (and
> now the multi-page versions) only write to kernel maps of user pages.
> That's why they can skip the access_ok(), stac/clac or uacess
> exception handling.

Bah, that namespace is a mess :/