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Re: [Qemu-devel] [PATCH] intel_iommu: handle invalid ce for shadow sync

From: Maxime Coquelin
Subject: Re: [Qemu-devel] [PATCH] intel_iommu: handle invalid ce for shadow sync
Date: Thu, 13 Sep 2018 10:16:20 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

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<address@hidden>
Tested-by: Pei Zhang<address@hidden>
CC: Pei Zhang<address@hidden>
CC: Alex Williamson<address@hidden>
CC: Jason Wang<address@hidden>
CC: Maxime Coquelin<address@hidden>
CC: Michael S. Tsirkin<address@hidden>
CC: QEMU Stable<address@hidden>

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<address@hidden>
  hw/i386/intel_iommu.c | 54 ++++++++++++++++++++++++++-----------------
  1 file changed, 33 insertions(+), 21 deletions(-)

Other than that, the patch looks good to me.
Acked-by: Maxime Coquelin <address@hidden>


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