linux-block.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Ira Weiny <ira.weiny@intel.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>,
	Thomas Gleixner <tglx@linutronix.de>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Geoff Levand <geoff@infradead.org>,
	Ilya Dryomov <idryomov@gmail.com>,
	Dongsheng Yang <dongsheng.yang@easystack.cn>,
	Mike Snitzer <snitzer@redhat.com>,
	"James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>,
	dm-devel@redhat.com, linux-mips@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
	linuxppc-dev@lists.ozlabs.org, ceph-devel@vger.kernel.org,
	linux-arch@vger.kernel.org,
	Herbert Xu <herbert@gondor.apana.org.au>,
	"David S. Miller" <davem@davemloft.net>
Subject: Re: [PATCH 01/18] mm: add a kunmap_local_dirty helper
Date: Thu, 17 Jun 2021 20:01:57 -0700	[thread overview]
Message-ID: <20210618030157.GA1905674@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20210615132456.753241-2-hch@lst.de>

On Tue, Jun 15, 2021 at 03:24:39PM +0200, Christoph Hellwig wrote:
> Add a helper that calls flush_kernel_dcache_page before unmapping the
> local mapping.  flush_kernel_dcache_page is required for all pages
> potentially mapped into userspace that were written to using kmap*,
> so having a helper that does the right thing can be very convenient.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  include/linux/highmem-internal.h | 7 +++++++
>  include/linux/highmem.h          | 4 ++++
>  2 files changed, 11 insertions(+)
> 
> diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
> index 7902c7d8b55f..bd37706db147 100644
> --- a/include/linux/highmem-internal.h
> +++ b/include/linux/highmem-internal.h
> @@ -224,4 +224,11 @@ do {								\
>  	__kunmap_local(__addr);					\
>  } while (0)
>  
> +#define kunmap_local_dirty(__page, __addr)			\

I think having to store the page and addr to return to kunmap_local_dirty() is
going to be a pain in some code paths.  Not a show stopper but see below...

> +do {								\
> +	if (!PageSlab(__page))					\

Was there some clarification why the page can't be a Slab page?  Or is this
just an optimization?

> +		flush_kernel_dcache_page(__page);		\

Is this required on 32bit systems?  Why is kunmap_flush_on_unmap() not
sufficient on 64bit systems?  The normal kunmap_local() path does that.

I'm sorry but I did not see a conclusion to my query on V1. Herbert implied the
he just copied from the crypto code.[1]  I'm concerned that this _dirty() call
is just going to confuse the users of kmap even more.  So why can't we get to
the bottom of why flush_kernel_dcache_page() needs so much logic around it
before complicating the general kernel users.

I would like to see it go away if possible.

Ira

[1] https://lore.kernel.org/lkml/20210615050258.GA5208@gondor.apana.org.au/

> +	kunmap_local(__addr);					\
> +} while (0)
> +
>  #endif
> diff --git a/include/linux/highmem.h b/include/linux/highmem.h
> index 832b49b50c7b..65f548db4f2d 100644
> --- a/include/linux/highmem.h
> +++ b/include/linux/highmem.h
> @@ -93,6 +93,10 @@ static inline void kmap_flush_unused(void);
>   * On HIGHMEM enabled systems mapping a highmem page has the side effect of
>   * disabling migration in order to keep the virtual address stable across
>   * preemption. No caller of kmap_local_page() can rely on this side effect.
> + *
> + * If data is written to the returned kernel mapping, the callers needs to
> + * unmap the mapping using kunmap_local_dirty(), else kunmap_local() should
> + * be used.
>   */
>  static inline void *kmap_local_page(struct page *page);
>  
> -- 
> 2.30.2
> 

  reply	other threads:[~2021-06-18  3:02 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-15 13:24 switch the block layer to use kmap_local_page v2 Christoph Hellwig
2021-06-15 13:24 ` [PATCH 01/18] mm: add a kunmap_local_dirty helper Christoph Hellwig
2021-06-18  3:01   ` Ira Weiny [this message]
2021-06-18  3:37     ` Herbert Xu
2021-06-18 18:12       ` Ira Weiny
2021-06-24  6:32         ` [PATCH] crypto: scatterwalk - Remove obsolete PageSlab check Herbert Xu
2021-06-15 13:24 ` [PATCH 02/18] mm: use kunmap_local_dirty in memcpy_to_page Christoph Hellwig
2021-06-15 13:24 ` [PATCH 03/18] mm: use kmap_local_page in memzero_page Christoph Hellwig
2021-06-15 13:24 ` [PATCH 04/18] MIPS: don't include <linux/genhd.h> in <asm/mach-rc32434/rb.h> Christoph Hellwig
2021-06-15 13:24 ` [PATCH 05/18] bvec: fix the include guards for bvec.h Christoph Hellwig
2021-06-15 13:24 ` [PATCH 06/18] bvec: add a bvec_kmap_local helper Christoph Hellwig
2021-06-16 16:52   ` [dm-devel] " Bart Van Assche
2021-06-15 13:24 ` [PATCH 07/18] bvec: add memcpy_{from,to}_bvec and memzero_bvec helper Christoph Hellwig
2021-06-15 13:24 ` [PATCH 08/18] block: use memzero_page in zero_fill_bio Christoph Hellwig
2021-06-15 13:24 ` [PATCH 09/18] rbd: use memzero_bvec Christoph Hellwig
2021-06-15 13:24 ` [PATCH 10/18] dm-writecache: use bvec_kmap_local instead of bvec_kmap_irq Christoph Hellwig
2021-06-15 13:24 ` [PATCH 11/18] ps3disk: use memcpy_{from,to}_bvec Christoph Hellwig
2021-06-16 16:36   ` Geoff Levand
2021-06-15 13:24 ` [PATCH 12/18] block: remove bvec_kmap_irq and bvec_kunmap_irq Christoph Hellwig
2021-06-15 13:24 ` [PATCH 13/18] block: rewrite bio_copy_data_iter to use bvec_kmap_local and memcpy_to_bvec Christoph Hellwig
2021-06-15 13:24 ` [PATCH 14/18] block: use memcpy_to_bvec in copy_to_high_bio_irq Christoph Hellwig
2021-06-15 13:24 ` [PATCH 15/18] block: use memcpy_from_bvec in bio_copy_kern_endio_read Christoph Hellwig
2021-06-15 13:24 ` [PATCH 16/18] block: use memcpy_from_bvec in __blk_queue_bounce Christoph Hellwig
2021-06-15 13:24 ` [PATCH 17/18] block: use bvec_kmap_local in t10_pi_type1_{prepare,complete} Christoph Hellwig
2021-06-15 13:24 ` [PATCH 18/18] block: use bvec_kmap_local in bio_integrity_process Christoph Hellwig
2021-06-16 16:03 ` switch the block layer to use kmap_local_page v2 Martin K. Petersen

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20210618030157.GA1905674@iweiny-DESK2.sc.intel.com \
    --to=ira.weiny@intel.com \
    --cc=James.Bottomley@HansenPartnership.com \
    --cc=axboe@kernel.dk \
    --cc=ceph-devel@vger.kernel.org \
    --cc=davem@davemloft.net \
    --cc=dm-devel@redhat.com \
    --cc=dongsheng.yang@easystack.cn \
    --cc=geoff@infradead.org \
    --cc=hch@lst.de \
    --cc=herbert@gondor.apana.org.au \
    --cc=idryomov@gmail.com \
    --cc=linux-arch@vger.kernel.org \
    --cc=linux-block@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mips@vger.kernel.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=snitzer@redhat.com \
    --cc=tglx@linutronix.de \
    --cc=tsbogend@alpha.franken.de \
    --subject='Re: [PATCH 01/18] mm: add a kunmap_local_dirty helper' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).