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Re: [Xen-devel] [PATCH 2/2] xl: Add "seize" option to PCI devices

On 03/04/2014 01:38 PM, George Dunlap wrote:
The "seize" option tells the toolstack to attempt to automatically
unbind devices and re-bind them to the pciback driver.  This should
make creating VMs that habitually use pass-through (such as driver domain
VMs and gaming VMs) easier to use and manage.

Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxxxxx>

Oops -- sorry, just realized that I had forgotten to add "LIBXL_HAS_PCI_SEIZE"...

While I'm here, might as well ask: I was going back and forth on this one, whether "seize" should actually be something passed in via the pci struct, as it's not really a property of the pci device itself. Other options would be:
1. Keep it out of libxl entirely: have the toolstack (in this case xl) do it
2. Have it done in libxl's domain creation
3. Make it an extra argument to libxl_pci_add()

When having my initial "second thoughts", #1 seemed most reasonable. But I'm not aware of any other such options handled in xl at the moment; this would be the only example of such an option.

Also, the current form allows someone to specify *which* devices to seize, which may be useful in some circumstances.

From a practical perspective, adding it to the struct makes it easy to add in the option without requiring an entirely new function for backwards compatibility.

So at the moment I'm inclined to leave it as it is; but I'm open to other ideas.


CC: Ian Jackson <ian.jackson@xxxxxxxxxx>
CC: Ian Campbell <ian.campbell@xxxxxxxxxx>
  docs/man/xl.cfg.pod.5       |   14 ++++++++++++++
  tools/libxl/libxl_pci.c     |    6 ++++++
  tools/libxl/libxl_types.idl |    1 +
  tools/libxl/libxlu_pci.c    |    2 ++
  tools/libxl/xl_cmdimpl.c    |    5 +++++
  5 files changed, 28 insertions(+)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index e15a49f..946b438 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -509,6 +509,15 @@ the PCI device regardless whether the guest uses INTx or 
MSI. Some
  device drivers, such as NVIDIA's, detect an inconsistency and do not
  function when this option is enabled. Therefore the default is false (0).

+=item B<seize=BOOLEAN>
+Tells xl to automatically attempt to re-assign a device to
+pciback if it is not already assigned.
+WARNING: If you set this option, xl will gladly re-assign a critical
+system device, such as a network or a disk controller being used by
+dom0 without confirmation.  Please use with care.
  =item B<power_mgmt=BOOLEAN>

  (HVM only) Specifies that the VM should be able to program the
@@ -530,6 +539,11 @@ above.
  Changes the default value of 'msitranslate' for all PCI devices passed
  through to this VM. See L<msitranslate|/"msitranslate_boolean"> above.

+=item B<pci_seize=BOOLEAN>
+Changes the default value of 'seize' for all PCI devices passed
+through to this VM. See L<seize|/"seize_boolean"> above.
  =item B<pci_power_mgmt=BOOLEAN>

  (HVM only) Changes the default value of 'power_mgmt' for all PCI
diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 2e52470..44d0453 100644
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -1050,6 +1050,12 @@ int libxl__device_pci_add(libxl__gc *gc, uint32_t domid, 
libxl_device_pci *pcide
      rc = libxl__device_pci_setdefault(gc, pcidev);
      if (rc) goto out;

+    if (pcidev->seize && !pciback_dev_is_assigned(gc, pcidev)) {
+        rc = libxl__device_pci_assignable_add(gc, pcidev, 1);
+        if ( rc )
+            goto out;
+    }
      if (!libxl_pcidev_assignable(ctx, pcidev)) {
          LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "PCI device %x:%x:%x.%x is not 
                     pcidev->domain, pcidev->bus, pcidev->dev, pcidev->func);
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 649ce50..7d3a62b 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -444,6 +444,7 @@ libxl_device_pci = Struct("device_pci", [
      ("msitranslate", bool),
      ("power_mgmt", bool),
      ("permissive", bool),
+    ("seize", bool),

  libxl_device_vtpm = Struct("device_vtpm", [
diff --git a/tools/libxl/libxlu_pci.c b/tools/libxl/libxlu_pci.c
index f5dee93..26fb143 100644
--- a/tools/libxl/libxlu_pci.c
+++ b/tools/libxl/libxlu_pci.c
@@ -141,6 +141,8 @@ int xlu_pci_parse_bdf(XLU_Config *cfg, libxl_device_pci 
*pcidev, const char *str
                      pcidev->power_mgmt = atoi(tok);
                  }else if ( !strcmp(optkey, "permissive") ) {
                      pcidev->permissive = atoi(tok);
+                }else if ( !strcmp(optkey, "seize") ) {
+                    pcidev->seize = atoi(tok);
                      XLU__PCI_ERR(cfg, "Unknown PCI BDF option: %s", optkey);
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index 4fc46eb..5f59bbc 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -737,6 +737,7 @@ static void parse_config_data(const char *config_source,
      int pci_power_mgmt = 0;
      int pci_msitranslate = 0;
      int pci_permissive = 0;
+    int pci_seize = 0;
      int i, e;

      libxl_domain_create_info *c_info = &d_config->c_info;
@@ -1462,6 +1463,9 @@ skip_vfb:
      if (!xlu_cfg_get_long (config, "pci_permissive", &l, 0))
          pci_permissive = l;

+    if (!xlu_cfg_get_long (config, "pci_seize", &l, 0))
+        pci_seize = l;
      /* To be reworked (automatically enabled) once the auto ballooning
       * after guest starts is done (with PCI devices passed in). */
      if (c_info->type == LIBXL_DOMAIN_TYPE_PV) {
@@ -1481,6 +1485,7 @@ skip_vfb:
              pcidev->msitranslate = pci_msitranslate;
              pcidev->power_mgmt = pci_power_mgmt;
              pcidev->permissive = pci_permissive;
+            pcidev->seize = pci_seize;
              if (!xlu_pci_parse_bdf(config, pcidev, buf))

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