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Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1plV3q-002jDf-Ec; Sun, 09 Apr 2023 13:26:26 +0000 Date: Sun, 9 Apr 2023 14:26:26 +0100 From: Matthew Wilcox To: Peter Zijlstra Cc: Ankur Arora , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, torvalds@linux-foundation.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, mgorman@suse.de, rostedt@goodmis.org, tglx@linutronix.de, vincent.guittot@linaro.org, jon.grimm@amd.com, bharata@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com Subject: Re: [PATCH 5/9] x86/clear_pages: add clear_pages() Message-ID: References: <20230403052233.1880567-1-ankur.a.arora@oracle.com> <20230403052233.1880567-6-ankur.a.arora@oracle.com> <20230406082304.GE386572@hirez.programming.kicks-ass.net> <878rf4jz1x.fsf@oracle.com> <20230407103444.GB430894@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230407103444.GB430894@hirez.programming.kicks-ass.net> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 2B91E180004 X-Rspam-User: X-Stat-Signature: gcz4rtjqrz6ticnbc5ftebti4a1iic1w X-HE-Tag: 1681046801-114222 X-HE-Meta: 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 lrLOHnbY 02DLhxp/2a0z7LpR8TqQ9bn+AvLzmFOma0IcxFRHA+muw333FI0SCYhP4dT+k42uFZxLK8Gben5gzdmwqnCbk9BVeE/RfhehxVrU3gvwOoh8IYrxrMKI+4CDJIKyOOpG8z/yFqmHKqySrF/4Q1GpHb845gxdRsF1h663HZJ0nDwjuejJRJe5ykyYEM6mDe/CKvj0h9tjyut/4JN2GE1uWLTPSlXhGgkimhbB86NXcwEwgoJT6ZP+8QZi1WkDzmGhpAC2DLRjUxm1SNALhy5WDNcMyXQBqze4T2YS6 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Apr 07, 2023 at 12:34:44PM +0200, Peter Zijlstra wrote: > On Thu, Apr 06, 2023 at 05:50:18PM -0700, Ankur Arora wrote: > > > > Peter Zijlstra 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 > > >> --- > > >> 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 :/ What (I think) it's suppsoed to be is that clear_page() works on kernel pages that are never seen by userspace while clear_user_page() works on kernel mappings of pages the user can definitely see. This makes no difference to x86, but some architectures can skip a lot of cache flushing.