diff mbox series

[v8,2/4] libxl: do not attach xen-pciback to HVM domain, if stubdomain is in use

Message ID 38b059a9d0a923c7d3f7eb24b675f6ab43863340.1569680095.git-series.marmarek@invisiblethingslab.com (mailing list archive)
State New, archived
Headers show
Series Fix PCI passthrough for HVM with stubdomain | expand

Commit Message

Marek Marczykowski-Górecki Sept. 28, 2019, 2:20 p.m. UTC 
HVM domains use IOMMU and device model assistance for communicating with
PCI devices, xen-pcifront/pciback isn't directly needed by HVM domain.
But pciback serve also second function - it reset the device when it is
deassigned from the guest and for this reason pciback needs to be used
with HVM domain too.
When HVM domain has device model in stubdomain, attaching xen-pciback to
the target domain itself may prevent attaching xen-pciback to the
(PV) stubdomain, effectively breaking PCI passthrough.

Fix this by attaching pciback only to one domain: if PV stubdomain is in
use, let it be stubdomain (the commit prevents attaching device to target
HVM in this case); otherwise, attach it to the target domain.

Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
---
Changes in v2:
 - previously called "libxl: attach xen-pciback only to PV domains"
 - instead of excluding all HVMs, change the condition to what actually
   matters here - check if stubdomain is in use; this way xen-pciback is
   always in use (either for the target domain, or it's stubdomain),
   fixing PCI reset by xen-pciback concerns
Changes in v3:
 - adjust commit message
Changes in v8:
 - rebase on staging
---
 tools/libxl/libxl_pci.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Ian Jackson Oct. 4, 2019, 4 p.m. UTC | #1 
Marek Marczykowski-Górecki writes ("[PATCH v8 2/4] libxl: do not attach xen-pciback to HVM domain, if stubdomain is in use"):
> HVM domains use IOMMU and device model assistance for communicating with
> PCI devices, xen-pcifront/pciback isn't directly needed by HVM domain.
> But pciback serve also second function - it reset the device when it is
> deassigned from the guest and for this reason pciback needs to be used
> with HVM domain too.
> When HVM domain has device model in stubdomain, attaching xen-pciback to
> the target domain itself may prevent attaching xen-pciback to the
> (PV) stubdomain, effectively breaking PCI passthrough.
> 
> Fix this by attaching pciback only to one domain: if PV stubdomain is in
> use, let it be stubdomain (the commit prevents attaching device to target
> HVM in this case); otherwise, attach it to the target domain.
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
> Acked-by: Wei Liu <wei.liu2@citrix.com>

FTR, this had a trivial conflict with 7988902b
  libxl_pci: Don't ignore PCI PT error at guest creation
which I am fixing up.

Ian.
diff mbox series

Patch

diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
index 2edff64..ac597a5 100644
--- a/tools/libxl/libxl_pci.c
+++ b/tools/libxl/libxl_pci.c
@@ -1399,7 +1399,7 @@  out_no_irq:
         }
     }
 
-    if (!starting)
+    if (!starting && !libxl_get_stubdom_id(CTX, domid))
         rc = libxl__device_pci_add_xenstore(gc, domid, pcidev, starting);
     else
         rc = 0;
@@ -1697,7 +1697,7 @@  static void add_pcidevs_done(libxl__egc *egc, libxl__multidev *multidev,
     libxl_domid domid = apds->domid;
     libxl__ao_device *aodev = apds->outer_aodev;
 
-    if (d_config->num_pcidevs > 0) {
+    if (d_config->num_pcidevs > 0 && !libxl_get_stubdom_id(CTX, domid)) {
         rc = libxl__create_pci_backend(gc, domid, d_config->pcidevs,
             d_config->num_pcidevs);
         if (rc < 0) {