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Re: [Qemu-devel] [PATCH qemu v5 04/12] spapr_pci_vfio: Enable multiple g


From: Alexey Kardashevskiy
Subject: Re: [Qemu-devel] [PATCH qemu v5 04/12] spapr_pci_vfio: Enable multiple groups per container
Date: Thu, 09 Apr 2015 17:13:34 +1000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0

On 04/09/2015 04:43 PM, David Gibson wrote:
On Wed, Apr 08, 2015 at 01:45:19PM +1000, Alexey Kardashevskiy wrote:
On 04/08/2015 12:01 PM, David Gibson wrote:
On Tue, Mar 31, 2015 at 04:28:39PM +1100, Alexey Kardashevskiy wrote:
This enables multiple IOMMU groups in one VFIO container which means
that multiple devices from different groups can share the same IOMMU
table (or tables if DDW).

This removes a group id from vfio_container_ioctl(). The kernel support
is required for this; if the host kernel does not have the support,
it will allow only one group per container. The PHB's "iommuid" property
is ignored.

This adds a sanity check that there is just one VFIO container per
PHB address space.

Signed-off-by: Alexey Kardashevskiy <address@hidden>

[snip]
diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index b012620..99e1900 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -915,21 +915,23 @@ void vfio_put_base_device(VFIODevice *vbasedev)
      close(vbasedev->fd);
  }

-static int vfio_container_do_ioctl(AddressSpace *as, int32_t groupid,
+static int vfio_container_do_ioctl(AddressSpace *as,
                                     int req, void *param)
  {
-    VFIOGroup *group;
      VFIOContainer *container;
-    int ret = -1;
+    int ret;
+    VFIOAddressSpace *space;

-    group = vfio_get_group(groupid, as);
-    if (!group) {
-        error_report("vfio: group %d not registered", groupid);
-        return ret;
-    }
+    space = vfio_get_address_space(as);
+    container = QLIST_FIRST(&space->containers);

So getting the container handle from the address space, rather than
the group id certainly makes more sense to me.

-    container = group->container;
-    if (group->container) {
+    if (!container) {
+        error_report("vfio: container is not set");
+        return -1;
+    } else if (QLIST_NEXT(container, next)) {
+        error_report("vfio: multiple containers per PHB are not supported");
+        return -1;

But if only one PHB per address space is possible, why is the
containers field a list in the first place?


Historically the list was added in 3df3e0a5872 (the patch of yours
:) ).

Heh.

In theory we could implement spapr-pci-bridge (derived from pci-bridge) with
isolation capability (i.e. its own LIOBN/DMA window), in this case there
could be multiple containers per PHB address space. Other archs could want
multiple containers for some other reason. It would help me a lot if you
remembered why you kept the list at the first place :)

Ok, I've looked over the patch and it has jogged my memory a bit.  So
the dumb answer is that it's because the per address-space list was
replacing a global list of containers

The more useful answer is that I think it was because I was
anticipating the possibility of working around the
one-group-per-container limit by allowing a single VFIOAddressSpace in
qemu to be backed by several containers, whose mappings would be kept
in sync from the userspace side by duplicating all mappings.

Anyway, I think that means the right way to implement this is by
duplicating the ioctl() across all the attached containers, rather
than picking just one.

Right. I will do that.


For now I guess I'll move the next patch ("vfio: spapr: Move SPAPR-related
code to a separate file") before this one, do s/vfio_container_do_ioctl/
vfio_spapr_container_do_ioctl/ and move it to hw/vfio/spapr.c. Makes
sense?

That sounds fine, though I don't see that it really addresses the
question here.

You are right, it does not. I won't do it in this patchset then. Thanks.







+    } else {
          ret = ioctl(container->fd, req, param);
          if (ret < 0) {
              error_report("vfio: failed to ioctl %d to container: ret=%d, %s",
@@ -937,12 +939,10 @@ static int vfio_container_do_ioctl(AddressSpace *as, 
int32_t groupid,
          }
      }

-    vfio_put_group(group);
-
      return ret;
  }

-int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
+int vfio_container_ioctl(AddressSpace *as,
                           int req, void *param)
  {
      /* We allow only certain ioctls to the container */
@@ -957,5 +957,5 @@ int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
          return -1;
      }

-    return vfio_container_do_ioctl(as, groupid, req, param);
+    return vfio_container_do_ioctl(as, req, param);
  }
diff --git a/include/hw/vfio/vfio.h b/include/hw/vfio/vfio.h
index 0b26cd8..76b5744 100644
--- a/include/hw/vfio/vfio.h
+++ b/include/hw/vfio/vfio.h
@@ -3,7 +3,7 @@

  #include "qemu/typedefs.h"

-extern int vfio_container_ioctl(AddressSpace *as, int32_t groupid,
+extern int vfio_container_ioctl(AddressSpace *as,
                                  int req, void *param);

  #endif






--
Alexey



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