From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0524CC433EF for ; Thu, 14 Apr 2022 07:03:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240211AbiDNHGJ (ORCPT ); Thu, 14 Apr 2022 03:06:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33226 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231582AbiDNHGG (ORCPT ); Thu, 14 Apr 2022 03:06:06 -0400 Received: from mail2-relais-roc.national.inria.fr (mail2-relais-roc.national.inria.fr [192.134.164.83]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5FA5028997; Thu, 14 Apr 2022 00:03:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=inria.fr; s=dc; h=date:from:to:cc:subject:in-reply-to:message-id: references:mime-version; bh=te3lUagj3c47Lhqa09adCixkLUiFDVwxje5+ZhtzTcc=; b=ZASy1r346Mf9/Cf0kmRziXpUVf6qit22lb/QCPcpntA5YPeNpys/9yss +r3cSRWU5lrgL2Gzhdvntutg1//7VyFGSOf/3xmlMhXo95ptouQ9cF73G PzgxDkvWRuTg/88ntufeuK3/eu3DrboKB1TcJDD/tza/Jq8Wbx3Zf/kX8 Y=; Authentication-Results: mail2-relais-roc.national.inria.fr; dkim=none (message not signed) header.i=none; spf=SoftFail smtp.mailfrom=julia.lawall@inria.fr; dmarc=fail (p=none dis=none) d=inria.fr X-IronPort-AV: E=Sophos;i="5.90,259,1643670000"; d="scan'208";a="31625224" Received: from 203.107.68.85.rev.sfr.net (HELO hadrien) ([85.68.107.203]) by mail2-relais-roc.national.inria.fr with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Apr 2022 09:03:41 +0200 Date: Thu, 14 Apr 2022 09:03:40 +0200 (CEST) From: Julia Lawall X-X-Sender: jll@hadrien To: Ira Weiny cc: Alison Schofield , "Fabio M. De Francesco" , Mauro Carvalho Chehab , Sakari Ailus , Greg Kroah-Hartman , Hans Verkuil , Tsuchiya Yuto , Martiros Shakhzadyan , Hans de Goede , linux-media@vger.kernel.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, outreachy@lists.linux.dev Subject: Re: [PATCH] staging: media: atomisp: Use kmap_local_page() in hmm_store() In-Reply-To: Message-ID: References: <20220413225531.9425-1-fmdefrancesco@gmail.com> <20220414004454.GA1243697@alison-desk> User-Agent: Alpine 2.22 (DEB 394 2020-01-19) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 13 Apr 2022, Ira Weiny wrote: > On Wed, Apr 13, 2022 at 05:44:54PM -0700, Alison Schofield wrote: > > On Thu, Apr 14, 2022 at 12:55:31AM +0200, Fabio M. De Francesco wrote: > > > The use of kmap() is being deprecated in favor of kmap_local_page() > > > where it is feasible. The same is true for kmap_atomic(). > > > > > > In file pci/hmm/hmm.c, function hmm_store() test if we are in atomic > > > context and, if so, it calls kmap_atomic(), if not, it calls kmap(). > > > > > > First of all, in_atomic() shouldn't be used in drivers. This macro > > > cannot always detect atomic context; in particular, it cannot know > > > about held spinlocks in non-preemptible kernels. > > > > > > Notwithstanding what it is said above, this code doesn't need to care > > > whether or not it is executing in atomic context. It can simply use > > > kmap_local_page() / kunmap_local() that can instead do the mapping / > > > unmapping regardless of the context. > > > > > > With kmap_local_page(), the mapping is per thread, CPU local and not > > > globally visible. Therefore, hmm_store()() is a function where the use > > > of kmap_local_page() in place of both kmap() and kmap_atomic() is > > > correctly suited. > > > > > > Convert the calls of kmap() / kunmap() and kmap_atomic() / > > > kunmap_atomic() to kmap_local_page() / kunmap_local() and drop the > > > unnecessary tests which test if the code is in atomic context. > > > > > > > Not specifically about this patch, but more generally about all > > such conversions - is there a 'proof' that shows this just works > > Just code inspection. Most of them that I have done have been compile tested > only. Part of the key is that des is a local variable and is not aliased by > anything outside this function. Typically, the concern about being in atomic context has to do with whether GFP_KERNEL or GFP_ATOMIC should be used, ie whether allocation can sleep. It doesn't have to do with whether some data can be shared. Is that the concern here? julia > > > or do we need to test each one. If the latter, then how? > > Generally there is no test if we don't have the hardware. Some of the more > difficult conversions will probably need to have some testing done but that > will need to be discussed with the subsystem maintainers at the time. > > Ira > > > > > > > > Signed-off-by: Fabio M. De Francesco > > > --- > > > drivers/staging/media/atomisp/pci/hmm/hmm.c | 14 ++------------ > > > 1 file changed, 2 insertions(+), 12 deletions(-) > > > > > > diff --git a/drivers/staging/media/atomisp/pci/hmm/hmm.c b/drivers/staging/media/atomisp/pci/hmm/hmm.c > > > index 46ac082cd3f1..54188197c3dc 100644 > > > --- a/drivers/staging/media/atomisp/pci/hmm/hmm.c > > > +++ b/drivers/staging/media/atomisp/pci/hmm/hmm.c > > > @@ -482,10 +482,7 @@ int hmm_store(ia_css_ptr virt, const void *data, unsigned int bytes) > > > idx = (virt - bo->start) >> PAGE_SHIFT; > > > offset = (virt - bo->start) - (idx << PAGE_SHIFT); > > > > > > - if (in_atomic()) > > > - des = (char *)kmap_atomic(bo->page_obj[idx].page); > > > - else > > > - des = (char *)kmap(bo->page_obj[idx].page); > > > + des = (char *)kmap_local_page(bo->page_obj[idx].page); > > > > > > if (!des) { > > > dev_err(atomisp_dev, > > > @@ -512,14 +509,7 @@ int hmm_store(ia_css_ptr virt, const void *data, unsigned int bytes) > > > > > > clflush_cache_range(des, len); > > > > > > - if (in_atomic()) > > > - /* > > > - * Note: kunmap_atomic requires return addr from > > > - * kmap_atomic, not the page. See linux/highmem.h > > > - */ > > > - kunmap_atomic(des - offset); > > > - else > > > - kunmap(bo->page_obj[idx].page); > > > + kunmap_local(des); > > > } > > > > > > return 0; > > > -- > > > 2.34.1 > > > > > > > >