> -----Original Message----- > From: Andrew Cooper > Sent: 14 March 2019 19:37 > To: Simon Gaiser <[email protected]>; Jason Andryuk > <[email protected]>; Paul Durrant > <[email protected]> > Cc: Anthony Perard <[email protected]>; > [email protected]; Stefano Stabellini > <[email protected]>; [email protected]; > [email protected] > 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 <[email protected]> > >> wrote: > >>>> -----Original Message----- > >>>> From: Jason Andryuk [mailto:[email protected]] > >>>> Sent: 11 March 2019 18:02 > >>>> To: [email protected] > >>>> Cc: [email protected]; [email protected]; > >>>> Simon Gaiser > >>>> <[email protected]>; Jason Andryuk <[email protected]>; > >>>> Stefano Stabellini > >>>> <[email protected]>; Anthony Perard <[email protected]>; > >>>> Paul Durrant > >>>> <[email protected]> > >>>> Subject: [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE > >>>> > >>>> From: Simon Gaiser <[email protected]> > >>>> > >>>> 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
