Hi Bharat, On 5/5/20 11:25 AM, Bharat Bhushan wrote: > 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. sorry I don't catch what you meant. Please can you elaborate?
Thanks Eric > > Stay Safe > > Thanks > -Bharat > >> >> Thanks >> >> Eric >>> >>> Thanks >>> -Bharat >>> >>>> >>>> Alex >>> >>> >> >