Hi Alex, Eric, > -----Original Message----- > From: Alex Williamson <alex.william...@redhat.com> > Sent: Thursday, March 26, 2020 11:23 PM > To: Auger Eric <eric.au...@redhat.com> > Cc: Bharat Bhushan <bbhush...@marvell.com>; peter.mayd...@linaro.org; > pet...@redhat.com; eric.auger....@gmail.com; kevin.t...@intel.com; > m...@redhat.com; Tomasz Nowicki [C] <tnowi...@marvell.com>; > drjo...@redhat.com; linuc.dec...@gmail.com; qemu-devel@nongnu.org; qemu- > a...@nongnu.org; bharatb.li...@gmail.com; jean-phili...@linaro.org; > yang.zh...@intel.com; David Gibson <da...@gibson.dropbear.id.au> > Subject: [EXT] Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio > region translation by viommu > > External Email > > ---------------------------------------------------------------------- > On Thu, 26 Mar 2020 18:35:48 +0100 > Auger Eric <eric.au...@redhat.com> wrote: > > > Hi Alex, > > > > On 3/24/20 12:08 AM, Alex Williamson wrote: > > > [Cc +dwg who originated this warning] > > > > > > On Mon, 23 Mar 2020 14:16:09 +0530 > > > Bharat Bhushan <bbhush...@marvell.com> wrote: > > > > > >> On ARM, the MSI doorbell is translated by the virtual IOMMU. > > >> As such address_space_translate() returns the MSI controller MMIO > > >> region and we get an "iommu map to non memory area" > > >> message. Let's remove this latter. > > >> > > >> Signed-off-by: Eric Auger <eric.au...@redhat.com> > > >> Signed-off-by: Bharat Bhushan <bbhush...@marvell.com> > > >> --- > > >> hw/vfio/common.c | 2 -- > > >> 1 file changed, 2 deletions(-) > > >> > > >> diff --git a/hw/vfio/common.c b/hw/vfio/common.c index > > >> 5ca11488d6..c586edf47a 100644 > > >> --- a/hw/vfio/common.c > > >> +++ b/hw/vfio/common.c > > >> @@ -426,8 +426,6 @@ static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, > void **vaddr, > > >> &xlat, &len, writable, > > >> MEMTXATTRS_UNSPECIFIED); > > >> if (!memory_region_is_ram(mr)) { > > >> - error_report("iommu map to non memory area %"HWADDR_PRIx"", > > >> - xlat); > > >> return false; > > >> } > > >> > > > > > > I'm a bit confused here, I think we need more justification beyond > > > "we hit this warning and we don't want to because it's ok in this > > > one special case, therefore remove it". I assume the special case > > > is that the device MSI address is managed via the SET_IRQS ioctl and > > > therefore we won't actually get DMAs to this range. > > Yes exactly. The guest creates a mapping between one giova and this > > gpa (corresponding to the MSI controller doorbell) because MSIs are > > mapped on ARM. But practically the physical device is programmed with > > an host chosen iova that maps onto the physical MSI controller's > > doorbell. so the device never performs DMA accesses to this range. > > > > But I imagine the case that > > > was in mind when adding this warning was general peer-to-peer > > > between and assigned and emulated device. > > yes makes sense. > > > > Maybe there's an argument to be made > > > that such a p2p mapping might also be used in a non-vIOMMU case. We > > > skip creating those mappings and drivers continue to work, maybe > > > because nobody attempts to do p2p DMA with the types of devices we > > > emulate, maybe because p2p DMA is not absolutely reliable on bare > > > metal and drivers test it before using it. > > MSI doorbells are mapped using the IOMMU_MMIO flag (dma-iommu.c > > iommu_dma_get_msi_page). > > One idea could be to pass that flag through the IOMMU Notifier > > mechanism into the iotlb->perm. Eventually when we get this in > > vfio_get_vaddr() we would not print the warning. Could that make sense? > > Yeah, if we can identify a valid case that doesn't need a warning, that's > fine by me. > Thanks,
Will change as per above suggestion by Eric. Thanks -Bharat > > Alex