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References: <20180913075517.11140-1-peterx@redhat.com>
From: Maxime Coquelin <maxime.coquelin@redhat.com>
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Date: Thu, 13 Sep 2018 10:16:20 +0200
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Subject: Re: [Qemu-devel] [PATCH] intel_iommu: handle invalid ce for shadow
 sync
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To: Peter Xu <peterx@redhat.com>, qemu-devel@nongnu.org
Cc: Pei Zhang <pezhang@redhat.com>, Alex Williamson <alex.williamson@redhat.com>, Jason Wang <jasowang@redhat.com>, "Michael S . Tsirkin" <mst@redhat.com>, QEMU Stable <qemu-stable@nongnu.org>

Hi Peter,

On 09/13/2018 09:55 AM, Peter Xu wrote:
> There are two callers for vtd_sync_shadow_page_table_range(), one
> provided a valid context entry and one not.  Move that fetching
> operation into the caller vtd_sync_shadow_page_table() where we need to
> fetch the context entry.
> 
> Meanwhile, we should handle VTD_FR_CONTEXT_ENTRY_P properly when
> synchronizing shadow page tables.  Having invalid context entry there is
> perfectly valid when we move a device out of an existing domain.  When
> that happens, instead of posting an error we invalidate the whole region.
> 
> Without this patch, QEMU will crash if we do these steps:
> 
> (1) start QEMU with VT-d IOMMU and two 10G NICs (ixgbe)
> (2) bind the NICs with vfio-pci in the guest
> (3) start testpmd with the NICs applied
> (4) stop testpmd
> (5) rebind the NIC back to ixgbe kernel driver
> 
> The patch should fix it.
> 
> Reported-by: Pei Zhang<pezhang@redhat.com>
> Tested-by: Pei Zhang<pezhang@redhat.com>
> CC: Pei Zhang<pezhang@redhat.com>
> CC: Alex Williamson<alex.williamson@redhat.com>
> CC: Jason Wang<jasowang@redhat.com>
> CC: Maxime Coquelin<maxime.coquelin@redhat.com>
> CC: Michael S. Tsirkin<mst@redhat.com>
> CC: QEMU Stable<qemu-stable@nongnu.org>
> Fixes:https://bugzilla.redhat.com/show_bug.cgi?id=1627272

It seems like a regression as it wasn't reported earlier, isn't it?
If it is, do you know what is the faulty commit?

> Signed-off-by: Peter Xu<peterx@redhat.com>
> ---
>   hw/i386/intel_iommu.c | 54 ++++++++++++++++++++++++++-----------------
>   1 file changed, 33 insertions(+), 21 deletions(-)

Other than that, the patch looks good to me.
FWIW:
Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime