> -----Original Message----- > From: Andrew Cooper > Sent: 14 March 2019 19:37 > To: Simon Gaiser <si...@invisiblethingslab.com>; Jason Andryuk > <jandr...@gmail.com>; Paul Durrant > <paul.durr...@citrix.com> > Cc: Anthony Perard <anthony.per...@citrix.com>; > xen-de...@lists.xenproject.org; Stefano Stabellini > <sstabell...@kernel.org>; qemu-devel@nongnu.org; > marma...@invisiblethingslab.com > Subject: Re: [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE > > On 14/03/2019 19:22, Simon Gaiser wrote: > > Jason Andryuk: > >> On Wed, Mar 13, 2019 at 11:09 AM Paul Durrant <paul.durr...@citrix.com> > >> wrote: > >>>> -----Original Message----- > >>>> From: Jason Andryuk [mailto:jandr...@gmail.com] > >>>> Sent: 11 March 2019 18:02 > >>>> To: qemu-devel@nongnu.org > >>>> Cc: xen-de...@lists.xenproject.org; marma...@invisiblethingslab.com; > >>>> Simon Gaiser > >>>> <si...@invisiblethingslab.com>; Jason Andryuk <jandr...@gmail.com>; > >>>> Stefano Stabellini > >>>> <sstabell...@kernel.org>; Anthony Perard <anthony.per...@citrix.com>; > >>>> Paul Durrant > >>>> <paul.durr...@citrix.com> > >>>> Subject: [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE > >>>> > >>>> From: Simon Gaiser <si...@invisiblethingslab.com> > >>>> > >>>> If a pci memory region has a size < XEN_PAGE_SIZE it can get located at > >>>> an address which is not page aligned. > >>> IIRC the PCI spec says that the minimum memory region size should be at > >>> least 4k. Should we even > be tolerating BARs smaller than that? > >>> > >>> Paul > >>> > >> Hi, Paul. > >> > >> Simon found this, so it affects a real device. Simon, do you recall > >> which device was affected? > > Not sure which one it was. Probably the USB controller or the SD host > > controller. As your example below shows this is not so uncommon. > > The minimum is 128 bytes, not 4k - I've just checked the PCIe spec. > > Xen/Qemu definitely needs to cope with smaller than 4k if we want to be > spec compliant.
Well, we have a problem for pass-through if the BAR is smaller than 4k in that page protection is not going to isolate it. I don't see any other way that to trap and emulate such BARs if we want to pass through those devices at all. Paul > > ~Andrew
