From owner-svn-src-head@freebsd.org Wed Nov 4 22:17:31 2015 Return-Path: Delivered-To: svn-src-head@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 37E6BA26565; Wed, 4 Nov 2015 22:17:31 +0000 (UTC) (envelope-from onwahe@gmail.com) Received: from mail-ig0-x22c.google.com (mail-ig0-x22c.google.com [IPv6:2607:f8b0:4001:c05::22c]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 01C6F1AC4; Wed, 4 Nov 2015 22:17:31 +0000 (UTC) (envelope-from onwahe@gmail.com) Received: by igbdj2 with SMTP id dj2so46025980igb.1; Wed, 04 Nov 2015 14:17:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; bh=xbNLrnv4NOOZ4Mv+qx5NBBKiBPP85doN8xC/Fdi4xRI=; b=EAsDIs98mkpraO9Dq6UL0CA0pG4ydAbp+0EHRmPrMx9F5N+n61HEyHo1KGLF7pjFb0 UgS56sLkqwO+/4umnyeah1beEWDzfqdwy+/W2A/kfvXHOVPJUMRB8rQKGhpGp8Oe6Xvv tGAQcBhX5ZiePDbiPJx84EIvXsH2DtynnS+UHGrcHspDrXklr2JHZtz+7vpx/XvMMsdN EQfVa8j4ysQ9b6YntVi3v/SmqEICWIphjlwydIfBrOqrOUqYiggu9ne25ko+z11L+YIg ZN4RiWPVVPtkkt4AD7jau6tBp4E5ThWUZ2IT59vSmEWxgJKKyvul4lZuoEu2KwKFCNMt NgHg== MIME-Version: 1.0 X-Received: by 10.50.22.39 with SMTP id a7mr5990697igf.42.1446675450389; Wed, 04 Nov 2015 14:17:30 -0800 (PST) Received: by 10.64.173.228 with HTTP; Wed, 4 Nov 2015 14:17:30 -0800 (PST) In-Reply-To: References: <201510221638.t9MGc1cc053885@repo.freebsd.org> <56348FF8.3010602@gmail.com> <1446394311.91534.236.camel@freebsd.org> Date: Wed, 4 Nov 2015 23:17:30 +0100 Message-ID: Subject: Re: svn commit: r289759 - in head/sys/arm: arm include From: Svatopluk Kraus To: Jason Harmening Cc: Ian Lepore , Ganbold Tsagaankhuu , src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Content-Type: text/plain; charset=UTF-8 X-BeenThere: svn-src-head@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: SVN commit messages for the src tree for head/-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 04 Nov 2015 22:17:31 -0000 On Tue, Nov 3, 2015 at 8:45 AM, Jason Harmening wrote: > > On Sun, Nov 1, 2015 at 8:11 AM, Ian Lepore wrote: >> >> >> It's almost certainly not related to sysinit ordering. This exception >> is happening during mmc probing after interrupts are enabled. >> >> It appears that the problem is the faulting code is running on one of >> the very early pre-allocated kernel stacks (perhaps in an interrupt >> handler on an idle thread stack), and these stacks are not in memory >> represented in the vm page arrays. The mmc code is using a 64-byte >> buffer on the stack and mapping it for DMA. Normally that causes a >> bounce for cacheline alignment, but unluckily in this case that buffer >> on the stack just happened to be aligned to a cacheline boundary and a >> multiple of the cacheline size, so no bounce. That causes the new sync >> logic that is based on keeping vm_page_t pointers and offsets to get a >> NULL pointer back from PHYS_TO_VM_PAGE when mapping, then it dies at >> sync time trying to dereference that. It used to work because the sync >> logic used to use the vaddr, not a page pointer. >> >> Michal was working on a patch yesterday. >> > > Ah, thanks for pointing that out Ian. I was left scratching my head > (admittedly on the road and w/o easy access to the code) wondering what on > earth would be trying to do DMA during SI_SUB_CPU. > Using of fictitious pages is not so easy here as in case pointed by kib@ where they are allocated and freed inside one function. For sync list sake, they must be allocated when a buffer is loaded and freed when is unloaded. Michal uses pmap_kextract() in case when KVA of buffer is not zero in his proof-of-concept patch: https://gist.github.com/strejda/d5ca3ed202427a2e0557 When KVA of buffer is not zero, temporary mapping is not used at all, so vm_page_t array is not needed too. IMO, buffer's physical address can be saved in sync list to be used when its KVA is not zero. Thus pmap_kextract() won't be called in dma_dcache_sync().