From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756770Ab0CaTSz (ORCPT ); Wed, 31 Mar 2010 15:18:55 -0400 Received: from charlotte.tuxdriver.com ([70.61.120.58]:53311 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756510Ab0CaTSy (ORCPT ); Wed, 31 Mar 2010 15:18:54 -0400 Date: Wed, 31 Mar 2010 15:18:11 -0400 From: Neil Horman To: "Eric W. Biederman" Cc: Vivek Goyal , iommu@lists.linux-foundation.org, joerg.roedel@amd.com, hbabu@us.ibm.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] amd iommu: force flush of iommu prior during shutdown Message-ID: <20100331191811.GD13406@hmsreliant.think-freely.org> References: <20100331152417.GB13406@hmsreliant.think-freely.org> <20100331155430.GF14011@redhat.com> <20100331182824.GC13406@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.20 (2009-08-17) X-Spam-Score: -2.9 (--) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 31, 2010 at 11:57:46AM -0700, Eric W. Biederman wrote: > Neil Horman writes: > > > On Wed, Mar 31, 2010 at 11:54:30AM -0400, Vivek Goyal wrote: > > >> So this call amd_iommu_flush_all_devices() will be able to tell devices > >> that don't do any more DMAs and hence it is safe to reprogram iommu > >> mapping entries. > >> > > It blocks the cpu until any pending DMA operations are complete. Hmm, as I > > think about it, there is still a small possibility that a device like a NIC > > which has several buffers pre-dma-mapped could start a new dma before we > > completely disabled the iommu, althought thats small. I never saw that in my > > testing, but hitting that would be fairly difficult I think, since its literally > > just a few hundred cycles between the flush and the actual hardware disable > > operation. > > > > According to this though: > > http://support.amd.com/us/Processor_TechDocs/34434-IOMMU-Rev_1.26_2-11-09.pdf > > That window could be closed fairly easily, but simply disabling read and write > > permissions for each device table entry prior to calling flush. If we do that, > > then flush the device table, any subsequently started dma operation would just > > get noted in the error log, which we could ignore, since we're abot to boot to > > the kdump kernel anyway. > > > > Would you like me to respin w/ that modification? > > Disabling permissions on all devices sounds good for the new virtualization > capable iommus. I think older iommus will still be challenged. I think > on x86 we have simply been able to avoid using those older iommus. > > I like the direction you are going but please let's put this in a > paranoid iommu enable routine. > You mean like initialize the device table so that all devices are default disabled on boot, and then selectively enable them (perhaps during a device_attach)? I can give that a spin. Neil > Eric > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >