From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Gibson Subject: Re: kvm PCI assignment & VFIO ramblings Date: Fri, 26 Aug 2011 14:24:23 +1000 Message-ID: <20110826042423.GF2308@yookeroo.fritz.box> References: <1312944513.29273.28.camel@pasglop> <1313859105.6866.192.camel@x201.home> <20110822172508.GJ2079@amd.com> <1314040622.6866.268.camel@x201.home> <20110823131441.GN2079@amd.com> <1314119311.2859.59.camel@bling.home> <20110824085213.GB2079@amd.com> <1314198467.2859.192.camel@bling.home> <20110825123146.GD1923@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Roedel, Joerg" , Alexey Kardashevskiy , "kvm@vger.kernel.org" , Paul Mackerras , qemu-devel , iommu , chrisw , Alex Williamson , Avi Kivity , Anthony Liguori , "linux-pci@vger.kernel.org" , linuxppc-dev , "benve@cisco.com" To: Alexander Graf Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-pci-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Thu, Aug 25, 2011 at 08:25:45AM -0500, Alexander Graf wrote: > > On 25.08.2011, at 07:31, Roedel, Joerg wrote: > > > On Wed, Aug 24, 2011 at 11:07:46AM -0400, Alex Williamson wrote: > >> On Wed, 2011-08-24 at 10:52 +0200, Roedel, Joerg wrote: > > > > [...] > > >> We need to try the polite method of attempting to hot unplug the device > >> from qemu first, which the current vfio code already implements. We can > >> then escalate if it doesn't respond. The current code calls abort in > >> qemu if the guest doesn't respond, but I agree we should also be > >> enforcing this at the kernel interface. I think the problem with the > >> hard-unplug is that we don't have a good revoke mechanism for the mmio > >> mmaps. > > > > For mmio we could stop the guest and replace the mmio region with a > > region that is filled with 0xff, no? > > Sure, but that happens in user space. The question is how does > kernel space enforce an MMIO region to not be mapped after the > hotplug event occured? Keep in mind that user space is pretty much > untrusted here - it doesn't have to be QEMU. It could just as well > be a generic user space driver. And that can just ignore hotplug > events. We're saying you hard yank the mapping from the userspace process. That is, you invalidate all its PTEs mapping the MMIO space, and don't let it fault them back in. As I see it there are two options: (a) make subsequent accesses from userspace or the guest result in either a SIGBUS that userspace must either deal with or die, or (b) replace the mapping with a dummy RO mapping containing 0xff, with any trapped writes emulated as nops. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson