Messages in this thread | | | From | "Sun, Ning" <> | Subject | RE: [RFC] x86/tboot: add an option to disable iommu force on | Date | Mon, 10 Apr 2017 21:28:46 +0000 |
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From tboot perspective, it is ok to add the option "tboot_noforce" to Linux kernel Intel_iommu parameter for those performance hungry tboot users, so long as the users are aware of the security implication behind of this option.
Thanks, -ning
-----Original Message----- From: Shaohua Li [mailto:shli@fb.com] Sent: Sunday, April 09, 2017 9:31 PM To: Sun, Ning <ning.sun@intel.com> Cc: Joerg Roedel <jroedel@suse.de>; linux-kernel@vger.kernel.org; Wei, Gang <gang.wei@intel.com>; hpa@linux.intel.com; mingo@kernel.org; kernel-team@fb.com; srihan@fb.com; Eydelberg, Alex <alex.eydelberg@intel.com> Subject: Re: [RFC] x86/tboot: add an option to disable iommu force on
On Fri, Apr 07, 2017 at 09:49:52PM +0000, Sun, Ning wrote: > Hi Shaohua, > > One question, did you still see the network performance penalty when Linux kernel cmdline intel_iommu was set to off ( intel_iommu=off) ?
the boot parameter has no effect, it runs very early and set dmar_disable=1. The tboot code (tboot_force_iommu) runs later and force dmar_disabled = 0.
Thanks, Shaohua > Thanks, > -ning > > -----Original Message----- > From: Joerg Roedel [mailto:jroedel@suse.de] > Sent: Friday, April 07, 2017 3:09 AM > To: Shaohua Li <shli@fb.com> > Cc: linux-kernel@vger.kernel.org; Wei, Gang <gang.wei@intel.com>; > hpa@linux.intel.com; mingo@kernel.org; kernel-team@fb.com; Sun, Ning > <ning.sun@intel.com>; srihan@fb.com; Eydelberg, Alex > <alex.eydelberg@intel.com> > Subject: Re: [RFC] x86/tboot: add an option to disable iommu force on > > On Mon, Apr 03, 2017 at 12:19:28PM -0700, Shaohua Li wrote: > > On Wed, Mar 22, 2017 at 07:50:55AM -0400, Shaohua Li wrote: > > > On Wed, Mar 22, 2017 at 11:49:00AM +0100, Joerg Roedel wrote: > > > > Hi Shaohua, > > > > > > > > On Tue, Mar 21, 2017 at 11:37:51AM -0700, Shaohua Li wrote: > > > > > IOMMU harms performance signficantly when we run very fast > > > > > networking workloads. This is a limitation in hardware based > > > > > on our observation, so we'd like to disable the IOMMU force > > > > > on, but we do want to use TBOOT and we can sacrifice the DMA > > > > > security bought by IOMMU. I must admit I know nothing about > > > > > TBOOT, but TBOOT guys (cc-ed) think not eabling IOMMU is totally ok. > > > > > > > > Can you elaborate a bit more on the setup where the IOMMU still > > > > harms network performance? With the recent scalability > > > > improvements I measured only a minimal impact on 10GBit networking. > > > Hi, > > > > > > It's 40GB networking doing XDP test. Software overhead is almost > > > unaware, but it's the IOTLB miss (based on our analysis) which > > > kills the performance. We observed the same performance issue even > > > with software passthrough (identity mapping), only the hardware > > > passthrough survives. The pps with iommu (with software passthrough) is only about ~30% of that without it. > > > > Any update on this? > > An explicit Ack from the tboot guys would be good to have. > > > Joerg >
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