Messages in this thread | | | Date | Tue, 14 Jun 2022 10:56:51 +0200 | Subject | Re: [PATCH v9 10/21] vfio/pci: introduce CONFIG_VFIO_PCI_ZDEV_KVM | From | Pierre Morel <> |
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On 6/8/22 15:15, Matthew Rosato wrote: > On 6/8/22 2:19 AM, Thomas Huth wrote: >> On 06/06/2022 22.33, Matthew Rosato wrote: >>> The current contents of vfio-pci-zdev are today only useful in a KVM >>> environment; let's tie everything currently under vfio-pci-zdev to >>> this Kconfig statement and require KVM in this case, reducing complexity >>> (e.g. symbol lookups). >>> >>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
>>> --- >>> drivers/vfio/pci/Kconfig | 11 +++++++++++ >>> drivers/vfio/pci/Makefile | 2 +- >>> include/linux/vfio_pci_core.h | 2 +- >>> 3 files changed, 13 insertions(+), 2 deletions(-) >>> >>> diff --git a/drivers/vfio/pci/Kconfig b/drivers/vfio/pci/Kconfig >>> index 4da1914425e1..f9d0c908e738 100644 >>> --- a/drivers/vfio/pci/Kconfig >>> +++ b/drivers/vfio/pci/Kconfig >>> @@ -44,6 +44,17 @@ config VFIO_PCI_IGD >>> To enable Intel IGD assignment through vfio-pci, say Y. >>> endif >>> +config VFIO_PCI_ZDEV_KVM >>> + bool "VFIO PCI extensions for s390x KVM passthrough" >>> + depends on S390 && KVM >>> + default y >>> + help >>> + Support s390x-specific extensions to enable support for >>> enhancements >>> + to KVM passthrough capabilities, such as interpretive >>> execution of >>> + zPCI instructions. >>> + >>> + To enable s390x KVM vfio-pci extensions, say Y. >> >> Is it still possible to disable CONFIG_VFIO_PCI_ZDEV_KVM ? Looking at >> the later patches (e.g. 20/21 where you call kvm_s390_pci_zpci_op() >> from kvm-s390.c), it rather seems to me that it currently cannot be >> disabled independently (as long as KVM is enabled). > > Yes, you can build with, for example, CONFIG_VFIO_PCI_ZDEV_KVM=n and > CONFIG_KVM=m -- I tested it again just now. The result is kvm and > vfio-pci are built and vfio-pci works, but none of the vfio-pci-zdev > extensions are available (including zPCI interpretation). > > This is accomplished via the placement of some IS_ENABLED checks. Some > calls (e.g. AEN init) are fenced by > IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM). There are also some areas that > are fenced off via a call to kvm_s390_pci_interp_allowed() which also > includes an IS_ENABLED check along with checks for facility and cpu id. > > Using patch 20 as an example, KVM_CAP_S390_ZPCI_OP will always be > reported as unavailable to userspace if CONFIG_VFIO_PCI_ZDEV_KVM=n due > to the call to kvm_s390_pci_interp_allowed(). If userspace sends us the > ioctl anyway, we will return -EINVAL because there is again a > IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM) check before we read the ioctl args > from userspace.
Yes and the code will not be generated by the compiler in patch 20 after the break if CONFIG_VFIO_PCI_ZDEV_KVM is not enabled.
+ case KVM_S390_ZPCI_OP: { + struct kvm_s390_zpci_op args; + + r = -EINVAL; + if (!IS_ENABLED(CONFIG_VFIO_PCI_ZDEV_KVM)) + break;
Code not generated----v
+ if (copy_from_user(&args, argp, sizeof(args))) { + r = -EFAULT; + break; + } + r = kvm_s390_pci_zpci_op(kvm, &args); + break;
----------^
+ } > >> >> So if you want to make this selectable by the user, I think you have >> to put some more #ifdefs in the following patches. >> But if this was not meant to be selectable by the user, I think it >> should not get a help text and rather be selected by the KVM switch in >> arch/s390/kvm/Kconfig instead of having a "default y". >> >> Thomas >> >
-- Pierre Morel IBM Lab Boeblingen
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