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From: Alex Williamson <alex.williamson@redhat.com>
To: Auger Eric <eric.auger@redhat.com>
Cc: yang.zhong@intel.com, peter.maydell@linaro.org,
	kevin.tian@intel.com, tnowicki@marvell.com, mst@redhat.com,
	drjones@redhat.com, peterx@redhat.com, qemu-devel@nongnu.org,
	bharatb.linux@gmail.com, qemu-arm@nongnu.org,
	jean-philippe@linaro.org, Bharat Bhushan <bbhushan2@marvell.com>,
	David Gibson <david@gibson.dropbear.id.au>,
	linuc.decode@gmail.com, eric.auger.pro@gmail.com
Subject: Re: [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio region translation by viommu
Date: Thu, 26 Mar 2020 11:53:18 -0600
Message-ID: <20200326115318.094ab79a@x1.home> (raw)
In-Reply-To: <8ec6af3c-6bd7-a3dc-c531-16db6b2089c5@redhat.com>

On Thu, 26 Mar 2020 18:35:48 +0100
Auger Eric <eric.auger@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 <bbhushan2@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.auger@redhat.com>
> >> Signed-off-by: Bharat Bhushan <bbhushan2@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,

Alex



  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-23  8:46 [PATCH v9 0/9] virtio-iommu: VFIO integration Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 1/9] hw/vfio/common: Remove error print on mmio region translation by viommu Bharat Bhushan
2020-03-23 23:08   ` Alex Williamson
2020-03-26 17:35     ` Auger Eric
2020-03-26 17:53       ` Alex Williamson [this message]
2020-03-27  5:50         ` [EXT] " Bharat Bhushan
2020-04-02  9:01         ` Bharat Bhushan
2020-04-24 14:17           ` Auger Eric
2020-05-05  9:25             ` Bharat Bhushan
2020-05-05  9:30               ` Auger Eric
2020-05-05  9:46                 ` Bharat Bhushan
2020-05-05 10:18                   ` Bharat Bhushan
2020-05-05 12:05                     ` Auger Eric
2020-05-07 14:40                     ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 2/9] memory: Add interface to set iommu page size mask Bharat Bhushan
2020-03-26 16:06   ` Auger Eric
2020-03-27  5:33     ` [EXT] " Bharat Bhushan
2020-03-27  8:27       ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 3/9] vfio: set iommu page size as per host supported page size Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 4/9] virtio-iommu: set supported page size mask Bharat Bhushan
2020-03-26 15:51   ` Auger Eric
2020-03-27  5:13     ` [EXT] " Bharat Bhushan
2020-03-27  8:28       ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 5/9] virtio-iommu: Add iommu notifier for map/unmap Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 6/9] virtio-iommu: Call iommu notifier for attach/detach Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 7/9] virtio-iommu: add iommu replay Bharat Bhushan
2020-03-23  8:46 ` [PATCH v9 8/9] virtio-iommu: Implement probe request Bharat Bhushan
2020-03-26 15:48   ` Auger Eric
2020-03-27  5:40     ` [EXT] " Bharat Bhushan
2020-03-27  8:34       ` Auger Eric
2020-04-23 16:09   ` Jean-Philippe Brucker
2020-04-24 13:51     ` Auger Eric
2020-05-05  9:06       ` Bharat Bhushan
2020-05-07 14:42         ` Auger Eric
2020-03-23  8:46 ` [PATCH v9 9/9] virtio-iommu: add iommu notifier memory-region Bharat Bhushan
2020-03-23  9:52 ` [PATCH v9 0/9] virtio-iommu: VFIO integration no-reply
2020-03-23  9:59 ` no-reply

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