[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH] QEMU as non-root and PCI passthrough do not mix
PCI passthrough cannot work if QEMU is run as a non-root process today, as QEMU needs to open /dev/mem to mmap the MSI-X table of the device and read/write relevant nodes on sysfs. Update the docs to reflect that. Run QEMU as root and print a warning if at least one PCI device has been assigned to the guest at domain creation. Print a debug message on pci hotplug. Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> diff --git a/docs/misc/qemu-deprivilege.txt b/docs/misc/qemu-deprivilege.txt index dde74ab..cf52547 100644 --- a/docs/misc/qemu-deprivilege.txt +++ b/docs/misc/qemu-deprivilege.txt @@ -29,3 +29,13 @@ adduser --no-create-home --system xen-qemuuser-shared 3) root As a last resort, libxl will start QEMU as root. + + +Please note that QEMU will still be run as root when PCI devices are +assigned to the virtual machine (if you specified pci=["$PCI_BDF"] in +your VM config file, where $PCI_BDF is the PCI BDF of the device you +want to assign). If you want to hotplug a PCI device sometime after the +VM has started, you need to make sure that the QEMU instance of that VM +has root privileges (for example by not specifying either +xen-qemuuser-shared or xen-qemuuser-domid$domid, or by giving root +privileges to xen-qemuuser-domid$domid). diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c index 0aaefd9..6b98750 100644 --- a/tools/libxl/libxl_dm.c +++ b/tools/libxl/libxl_dm.c @@ -1254,6 +1254,12 @@ static int libxl__build_device_model_args_new(libxl__gc *gc, break; } + /* Do not run QEMU as non-root if PCI devices are assigned */ + if (guest_config->num_pcidevs > 0) { + LOG(WARN, "Cannot run QEMU as non-root when PCI devices are being assigned to the guest VM"); + goto end_search; + } + if (b_info->device_model_user) { user = b_info->device_model_user; goto end_search; diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c index dc10cb7..04d0dd4 100644 --- a/tools/libxl/libxl_pci.c +++ b/tools/libxl/libxl_pci.c @@ -1176,6 +1176,9 @@ int libxl_device_pci_add(libxl_ctx *ctx, uint32_t domid, { AO_CREATE(ctx, domid, ao_how); int rc; + + LOG(DEBUG, "QEMU needs to be run as root for PCI passthrough to work"); + rc = libxl__device_pci_add(gc, domid, pcidev, 0); libxl__ao_complete(egc, ao, rc); return AO_INPROGRESS; _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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