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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id i12si2096308pgq.466.2019.02.15.00.57.42 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 15 Feb 2019 00:57:42 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=gT8IzfYM; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=lC0sJXKkNVKrNcwoJXfFFpIZaHgwwYjVNEpuiQ0lz3E=; b=gT8IzfYM0rLFTG1VADzNxWfkL 0eTJScOywY+BgA5bL80r6zjO1AZl0H1zn29CTmFlZpu9sIc1WYqCtNA2bv/sLQy+V7B5KSUJL9kBf Mjc3XlxeAS2Al3t6/Whmm/lamblTaQI4AOdXw4EJkWBnRgFshT9ee/IpFzmm8tY1oqVPt1WRJewMQ wg8kTdGA4sk4TirfNw88ZtdtbGnDMH45veEYZy1uMspmPpNxOUFG+XJ9YCgDMkUqaGfGURYZIExdP N88tGKmHqC9VA5C/vAfXJZLPzY1ecvbeTU9gZV2OI7fGkQGeoFyBBHE8kTs/NXjsX9OU67Bl1b2ZI 4/Q6jy/xQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1guZJT-0000As-Ke; Fri, 15 Feb 2019 08:57:39 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id EE255201A8970; Fri, 15 Feb 2019 09:57:36 +0100 (CET) Date: Fri, 15 Feb 2019 09:57:36 +0100 From: Peter Zijlstra To: Igor Stoppa Cc: Igor Stoppa , Andy Lutomirski , Nadav Amit , Matthew Wilcox , Kees Cook , Dave Hansen , Mimi Zohar , Thiago Jung Bauermann , Ahmed Soliman , linux-integrity@vger.kernel.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH v5 03/12] __wr_after_init: Core and default arch Message-ID: <20190215085736.GO32494@hirez.programming.kicks-ass.net> References: <20190214112849.GM32494@hirez.programming.kicks-ass.net> <6e9ec71c-ee75-9b1e-9ff8-a3210030e85d@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6e9ec71c-ee75-9b1e-9ff8-a3210030e85d@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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, Feb 15, 2019 at 01:10:33AM +0200, Igor Stoppa wrote: > > > On 14/02/2019 13:28, Peter Zijlstra wrote: > > On Thu, Feb 14, 2019 at 12:41:32AM +0200, Igor Stoppa wrote: > > [...] > > > > +#define wr_rcu_assign_pointer(p, v) ({ \ > > > + smp_mb(); \ > > > + wr_assign(p, v); \ > > > + p; \ > > > +}) > > > > This requires that wr_memcpy() (through wr_assign) is single-copy-atomic > > for native types. There is not a comment in sight that states this. > > Right, I kinda expected native-aligned <-> atomic, but it's not necessarily > true. It should be confirmed when enabling write rare on a new architecture. > I'll add the comment. > > > Also, is this true of x86/arm64 memcpy ? > > > For x86_64: > https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/x86/include/asm/uaccess.h#L462 > the mov"itype" part should deal with atomic copy of native, aligned types. > > > For arm64: > https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/arm64/lib/copy_template.S#L110 > .Ltiny15 deals with copying less than 16 bytes, which includes pointers. > When the data is aligned, the copy of a pointer should be atomic. > Where are the comments and Changelog notes ? How is an arch maintainer to be aware of this requirement when adding support for his/her arch?