[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [xen stable-4.16] libxl/PCI: Fix PV hotplug & stubdom coldplug
commit 8509519268ea6a467a97ca7891a0dca2bfe88cf7 Author: Jason Andryuk <jandryuk@xxxxxxxxx> AuthorDate: Tue Jan 25 13:38:14 2022 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Tue Jan 25 13:38:14 2022 +0100 libxl/PCI: Fix PV hotplug & stubdom coldplug 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 2) The domain is running 3) The backend is already present This is because: 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 <jandryuk@xxxxxxxxx> Reviewed-by: Paul Durrant <paul@xxxxxxx> Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx> master commit: 73ee2795aaef2cb086ac078bffe1c6b33c0ea91b master date: 2022-01-13 14:33:16 +0100 --- 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); -- generated by git-patchbot for /home/xen/git/xen.git#stable-4.16
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