Re: [Qemu-devel] [PATCH 0/4] exec: address space translation cleanups

[Peter Xu <peterx@redhat.com>]

On Wed, May 17, 2017 at 12:23:42PM +0800, Peter Xu wrote:
> On Tue, May 16, 2017 at 06:51:03PM +0200, Maxime Coquelin wrote:
> > Hi Peter,
> > 
> > On 05/16/2017 03:24 PM, Maxime Coquelin wrote:
> > >
> > >
> > >On 05/15/2017 10:50 AM, Peter Xu wrote:
> > >>The problem is that, address_space_get_iotlb_entry() shares a lot with
> > >>address_space_translate(). This patch tries to abstract the
> > >>shared elements.
> > >>
> > >>Originally, this work is derived from discussion from VT-d passthrough
> > >>series discussions [1]. But for sure we can just see this series as a
> > >>standalone cleanup. So I posted it separately here.
> > >>
> > >>Smoke tests are done with general VM boots, IOs, especially with vhost
> > >>dmar configurations.
> > >>
> > >>I believe with current series I can throw away the old patch [1],
> > >>which may be good. But before that, please kindly review. Thanks.
> > >
> > >I faced the problem the old patch fixes when declaring and attaching an
> > >IOMMU device, but booting the kernel with intel_iommu=off.
> > >
> > >I tested again with patches 1 & 4 of your series, and I confirm it fixes
> > >the issue:
> > >Tested-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> > 
> > I did some more testing with my "vhost-user IOMMU" setup, and the series
> > actually breaks with IOMMU device attached, and intel_iommu=on.
> > 
> > The main difference with the previous passing test is the guest RAM
> > size. In the working setup, it is 2G of 2M hugepages, vs. 4G of 2M
> > hugepages in the failing one. Note that I also reproduce with vhost-kernel
> > backend.
> > 
> > The error happens in the first vhost_device_iotlb_miss() call:
> > qemu-system-x86_64: Fail to lookup the translated address b5d7c000
> > 
> > I don't have the root cause yet, I'll keep you updated.
> 
> Maxime,
> 
> Thanks a lot for help testing this series!
> 
> I reproduced this problem, and this is not a problem obvious enough
> for me. Let me investigate as well.
> 
> -- 
> Peter Xu

Maxime,

Could you help try adding this change upon current to see whether
problem solved?

diff --git a/exec.c b/exec.c
index 697d902..68576a2 100644
--- a/exec.c
+++ b/exec.c
@@ -521,6 +521,10 @@ IOMMUTLBEntry address_space_get_iotlb_entry(AddressSpace *as, hwaddr addr,
         goto iotlb_fail;
     }
 
+    /* Convert memory region offset into address space offset */
+    xlat += section.offset_within_address_space -
+        section.offset_within_region;
+
     if (plen == (hwaddr)-1) {
         /*
          * We use default page size here. Logically it only happens

Thanks in advance,

-- 
Peter Xu