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.
Thanks Eric > > Thanks > -Bharat > >> >> Alex > >