From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gary Kroening Subject: Re: [RFC] iommu/vt-d: Use the SIRTP when enabling remapping Date: Wed, 10 Sep 2014 02:58:46 -0500 Message-ID: <541004B6.8070800@sgi.com> References: <1410297096-54096-1-git-send-email-nzimmer@sgi.com> <540FF614.8000003@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <540FF614.8000003@siemens.com> Sender: linux-kernel-owner@vger.kernel.org To: Jan Kiszka , Nathan Zimmer , jroedel@suse.de Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org On 9/10/2014 1:56 AM, Jan Kiszka wrote: > On 2014-09-09 23:11, Nathan Zimmer wrote: >> The previous change (iommu/vt-d: Don't store SIRTP request) to this area >> caused a crash in our simulator. In particular is seems that by the time a >> UART interrupt is sent through the system, we don't see interrupt remapping >> to be enabled. So the interrupt does not get translated to a logical >> interrupt and crashes. >> >> OR'ing the SIRTP request to make sure it is seen but hopefully not sticky. >> This seems like a clean fix, at least on our simulator; if you don't agree, >> our simulator guy will take a closer look at our iommu model. > > Check the VT-d spec (6.7, Set Interrupt Remapping Table Pointer > Operation): "Software must always follow the interrupt-remapping table > pointer set operation with a global invalidate of the IEC to ensure > hardware references the new structures *before* enabling interrupt > remapping." There is also (command register description): "If multiple > control fields in this register need to be modified, software must > serialize the modifications through multiple writes to this register." > This, in combination with the command registers description of bits 24 > and 25 strongly suggests that your model is broken. Thanks, Jan. I'll read up on it. Still working out some kinks with the relatively new IOMMU/interrupt-remapping logic which we added over the last 18 months or so. Sorry for any distraction, and thanks for the help/info. Gary > >> >> Found testing on our simulator, not real hardware. > > Funnily, the original issue was found by the QEMU model of VT-d that > used to take the last cited sentence very strictly (I asked to remove it > due to the preexisting Linux versions). > > Jan >