Hi Eric, On Fri, Apr 24, 2020 at 7:47 PM Auger Eric <eric.au...@redhat.com> wrote: > > Hi Bharat, > > On 4/2/20 11:01 AM, Bharat Bhushan wrote: > > Hi Eric/Alex, > > > >> -----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, > > > > Let me know if I understood the proposal correctly: > > > > virtio-iommu driver in guest will make map (VIRTIO_IOMMU_T_MAP) with > > VIRTIO_IOMMU_MAP_F_MMIO flag for MSI mapping. > > In qemu, virtio-iommu device will set a new defined flag (say IOMMU_MMIO) > > in iotlb->perm in memory_region_notify_iommu(). vfio_get_vaddr() will check > > same flag and will not print the warning.> > > Is above correct? > Yes that's what I had in mind.
In that case virtio-iommu driver in guest should not make map (VIRTIO_IOMMU_T_MAP) call as it known nothing to be mapped. Stay Safe Thanks -Bharat > > Thanks > > Eric > > > > Thanks > > -Bharat > > > >> > >> Alex > > > > >