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Tsirkin" Message-ID: <20190916033501.GE14232@xz-x1> References: <20190812074531.28970-1-peterx@redhat.com> <20190820052240.GG13560@xz-x1> <20190821050302.GA25454@xz-x1> <8106168f-1648-5823-8a69-f93638c74c66@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <8106168f-1648-5823-8a69-f93638c74c66@redhat.com> User-Agent: Mutt/1.11.4 (2019-03-13) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH RFC 0/4] intel_iommu: Do sanity check of vfio-pci earlier X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Alex Williamson , Eduardo Habkost , "Michael S. Tsirkin" , Jason Wang , qemu-devel@nongnu.org, Bandan Das , Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= , Paolo Bonzini , Igor Mammedov , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Aug 21, 2019 at 09:50:43AM +0200, Paolo Bonzini wrote: > On 21/08/19 07:03, Peter Xu wrote: > > On Tue, Aug 20, 2019 at 08:24:49AM +0200, Paolo Bonzini wrote: > >> On 20/08/19 07:22, Peter Xu wrote: > >>> On Mon, Aug 12, 2019 at 09:45:27AM +0200, Peter Xu wrote: > >>>> This is a RFC series. > >>>> > >>>> The VT-d code has some defects, one of them is that we cannot detect > >>>> the misuse of vIOMMU and vfio-pci early enough. > >>>> > >>>> For example, logically this is not allowed: > >>>> > >>>> -device intel-iommu,caching-mode=off \ > >>>> -device vfio-pci,host=05:00.0 > >>>> > >>>> Because the caching mode is required to make vfio-pci devices > >>>> functional. > >>>> > >>>> Previously we did this sanity check in vtd_iommu_notify_flag_changed() > >>>> as when the memory regions change their attributes. However that's > >>>> too late in most cases! Because the memory region layouts will only > >>>> change after IOMMU is enabled, and that's in most cases during the > >>>> guest OS boots. So when the configuration is wrong, we will only bail > >>>> out during the guest boots rather than simply telling the user before > >>>> QEMU starts. > >>>> > >>>> The same problem happens on device hotplug, say, when we have this: > >>>> > >>>> -device intel-iommu,caching-mode=off > >>>> > >>>> Then we do something like: > >>>> > >>>> (HMP) device_add vfio-pci,host=05:00.0,bus=pcie.1 > >>>> > >>>> If at that time the vIOMMU is enabled in the guest then the QEMU > >>>> process will simply quit directly due to this hotplug event. This is > >>>> a bit insane... > >>>> > >>>> This series tries to solve above two problems by introducing two > >>>> sanity checks upon these places separately: > >>>> > >>>> - machine done > >>>> - hotplug device > >>>> > >>>> This is a bit awkward but I hope this could be better than before. > >>>> There is of course other solutions like hard-code the check into > >>>> vfio-pci but I feel it even more unpretty. I didn't think out any > >>>> better way to do this, if there is please kindly shout out. > >>>> > >>>> Please have a look to see whether this would be acceptable, thanks. > >>> > >>> Any more comment on this? > >> > >> No problem from me, but I wouldn't mind if someone else merged it. :) > > > > Can I read this as an "acked-by"? :) > > Yes, it shouldn't even need Acked-by since there are other maintainers > that handle this part of the tree: > > Paolo Bonzini (maintainer:X86 TCG CPUs) > Richard Henderson (maintainer:X86 TCG CPUs) > Eduardo Habkost (maintainer:X86 TCG CPUs) > "Michael S. Tsirkin" (supporter:PC) > Marcel Apfelbaum (supporter:PC) Michael (or any maintainers listed above): Do any of you have any further comment on this series? Do any of you like to merge this? Thanks, -- Peter Xu