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-de...@nongnu.org >>> Cc: xen-devel@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? > > I think BARs only need to be power-of-two size and aligned, and 4k is > not a minimum. 16bytes may be a minimum, but I don't know what the > spec says. > > On an Ivy Bridge system, here are some of the devices with BARs smaller than > 4K: > 00:16.0 Communication controller: Intel Corporation 7 Series/C210 > Series Chipset Family MEI Controller #1 (rev 04) > Memory at d0735000 (64-bit, non-prefetchable) [disabled] [size=16] > 00:1d.0 USB controller: Intel Corporation 7 Series/C210 Series Chipset > Family USB Enhanced Host Controller #1 (rev 04) (prog-if 20 [EHCI]) > Memory at d0739000 (32-bit, non-prefetchable) [disabled] [size=1K] > 00:1f.3 SMBus: Intel Corporation 7 Series/C210 Series Chipset Family > SMBus Controller (rev 04) > Memory at d0734000 (64-bit, non-prefetchable) [disabled] [size=256] > 02:00.0 System peripheral: JMicron Technology Corp. SD/MMC Host > Controller (rev 30) > Memory at d0503000 (32-bit, non-prefetchable) [disabled] [size=256] > > These examples are all 4K aligned, so this is not an issue on this machine.
I wrote this patch quite some time ago, so I might be misremembering something but IIRC the problem was the address qemu allocates with memory_region_init_io(). I.e. the address as seen from inside the VM, so it does not help if the real address is aligned.
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