Re: [libvirt] [PATCH v2] util: disallow assigning or resetting a pci-bridge device

On 01/18/2017 11:10 AM, Martin Kletzander wrote: > On Wed, Jan 18, 2017 at 07:29:29PM +0530, Shivaprasad G Bhat wrote: >> It is destructive to attempt reset on a pci-bridge, the host can crash. >> The bridges won't contain any guest data and neither they can be >> passed through using vfio/stub. So, no point in allowing a reset on >> them. >> > > Wasn't resetting non-endpoint the only way in some cases when you needed > to passthrough 2 endpoint devices when none of them could be reset? I > might be very easily wrong, though. What you're thinking of is the code in virPCIDeviceReset() that attempts to do a "secondary bus reset" on the parent of an endpoint device if the reset of the endpoint device itself fails. This is never initiated directly by the user (or the top level of the libvirt API) though, but only done internally when attempts to reset an endpoint device fail (libvirt then tries doing a secondary bus reset of the endpoint's parent device). Of course *all* of the PCI reset stuff in libvirt is a moot point if you're using vfio anyway - vfio itself will handle any device resets that need to be done at the appropriate time. That's why virPCIDeviceReset() returns success almost immediately if the device is bound to vfio-pci. Since the only time the device would *not* be bound to vfio-pci would be 1) if a domain was using legacy KVM device assignment (which is deprecated, and I think may even be completely removed from new kernels) or 2) if a user manually requested a device reset with libvirt's virNodeDeviceReset() API (which realistically speaking nobody should ever need to do), there's really not much chance of this making an actual difference. (This makes me wonder where Shivaprasad encountered this in the real world...)

> >> Signed-off-by: Shivaprasad G Bhat <sbhat(a)linux.vnet.ibm.com&gt; >> --- >> src/util/virhostdev.c | 10 ++++++++++ >> src/util/virpci.c | 11 +++++++++++ >> 2 files changed, 21 insertions(+) >> >> diff --git a/src/util/virhostdev.c b/src/util/virhostdev.c >> index 0673afb..16b96f3 100644 >> --- a/src/util/virhostdev.c >> +++ b/src/util/virhostdev.c >> @@ -532,6 +532,16 @@ >> virHostdevPreparePCIDevices(virHostdevManagerPtr mgr, >> bool strict_acs_check = !!(flags & >> VIR_HOSTDEV_STRICT_ACS_CHECK); >> bool usesVFIO = (virPCIDeviceGetStubDriver(pci) == >> VIR_PCI_STUB_DRIVER_VFIO); >> struct virHostdevIsPCINodeDeviceUsedData data = { mgr, >> dom_name, usesVFIO }; >> + int hdrType = -1; >> + >> + if (virPCIGetHeaderType(pci, &hdrType) < 0) >> + goto cleanup; >> + >> + if (hdrType == VIR_PCI_HEADER_PCI_BRIDGE) { I verified with the VFIO author/maintainer (Alex Williamson) that vfio will assign only endpoint devices - cardbus bridge devices and PCI bridge devices are both not allowed. So I think that this check should also be for "hdrType != VIR_PCI_HEADER_ENDPOINT". Also, it's kind of nit-picking, but I think this chunk should be in a separate patch from the other. One is preventing attempts to assign a device that isn't an endpoint, and the otehr is preventing attemps to reset a device that isn't an endpoint. >> + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", _("PCI bridge devices" >> + " cannot be assigned to guests")); When a string is split into multiple lines, the final character of each line's substring must be a space (this is in the contribution guidelines and is enforced by make syntax-check)

>> + goto cleanup; >> + } >> >> if (!usesVFIO && !virPCIDeviceIsAssignable(pci, >> strict_acs_check)) { >> virReportError(VIR_ERR_OPERATION_INVALID, >> diff --git a/src/util/virpci.c b/src/util/virpci.c >> index 0601f49..f205abf 100644 >> --- a/src/util/virpci.c >> +++ b/src/util/virpci.c >> @@ -933,6 +933,17 @@ virPCIDeviceReset(virPCIDevicePtr dev, >> char *drvName = NULL; >> int ret = -1; >> int fd = -1; >> + int hdrType = -1; >> + >> + if (virPCIGetHeaderType(dev, &hdrType) < 0) >> + return -1; >> + >> + if (hdrType != VIR_PCI_HEADER_ENDPOINT) { >> + virReportError(VIR_ERR_INTERNAL_ERROR, >> + _("Invalid attempt to reset non-endpoint PCI >> device %s." >> + " Only PCI endpoint devices can be >> reset"), dev->name); Same problem. make syntax-check will catch it. If you split this in two, change the first check to be for != endpoint rather than == bridge, and fix the strings, then these can be pushed.