On 13/01/2022 04:01, Jason Andryuk wrote:
commit 0fdb48ffe7a1 "libxl: Make sure devices added by pci-attach are
reflected in the config" broken PCI hotplug (xl pci-attach) for PV
domains when it moved libxl__create_pci_backend() later in the function.
This also broke HVM + stubdom PCI passthrough coldplug. For that, the
PCI devices are hotplugged to a running PV stubdom, and then the QEMU
QMP device_add commands are made to QEMU inside the stubdom.
A running PV domain calls libxl__wait_for_backend(). With the current
placement of libxl__create_pci_backend(), the path does not exist and
the call immediately fails:
libxl: error: libxl_device.c:1388:libxl__wait_for_backend: Backend
/local/domain/0/backend/pci/43/0 does not exist
libxl: error: libxl_pci.c:1764:device_pci_add_done: Domain
42:libxl__device_pci_add failed for PCI device 0:2:0.0 (rc -3)
libxl: error: libxl_create.c:1857:domcreate_attach_devices: Domain 42:unable to
add pci devices
The wait is only relevant when:
1) The domain is PV
3) The domain is running
2) The backend is already present
The numbering above needs fixing and I guess you want a "Because..." here.
1) xen-pcifront is only used for PV. It does not load for HVM domains
where QEMU is used.
2) If the domain is not running (starting), then the frontend state will
be Initialising. xen-pciback waits for the frontend to transition to
at Initialised before attempting to connect. So a wait for a
non-running domain is not applicable as the backend will not
transition to Connected.
3) For presence, num_devs is already used to determine if the backend
needs to be created. Re-use num_devs to determine if the backend
wait is necessary. The wait is necessary to avoid racing with
another PCI attachment reconfiguring the front/back or changing to
some other state like closing. If we are creating the backend, then
we don't have to worry about the state since it is being created.
Fixes: 0fdb48ffe7a1 ("libxl: Make sure devices added by pci-attach are
reflected in the config")
Signed-off-by: Jason Andryuk <jandr...@gmail.com>
Reviewed-by: Paul Durrant <p...@xen.org>
---
Alternative to Jan's patch:
https://lore.kernel.org/xen-devel/5114ae87-bc0e-3d58-e16e-6d9d2fee0...@suse.com/
v4:
Use if (rc) return rc
Capitalize comment sentence
Change commit message
v3:
Change title & commit message
v2:
Add Fixes
Expand num_devs use in commit message
---
tools/libs/light/libxl_pci.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
index 4c2d7aeefb..4bbbfe9f16 100644
--- a/tools/libs/light/libxl_pci.c
+++ b/tools/libs/light/libxl_pci.c
@@ -157,9 +157,11 @@ static int libxl__device_pci_add_xenstore(libxl__gc *gc,
if (domtype == LIBXL_DOMAIN_TYPE_INVALID)
return ERROR_FAIL;
- if (!starting && domtype == LIBXL_DOMAIN_TYPE_PV) {
- if (libxl__wait_for_backend(gc, be_path, GCSPRINTF("%d",
XenbusStateConnected)) < 0)
- return ERROR_FAIL;
+ /* Wait is only needed if the backend already exists (num_devs != NULL) */
+ if (num_devs && !starting && domtype == LIBXL_DOMAIN_TYPE_PV) {
+ rc = libxl__wait_for_backend(gc, be_path,
+ GCSPRINTF("%d", XenbusStateConnected));
+ if (rc) return rc;
}
back = flexarray_make(gc, 16, 1);
