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Message-ID: <ac5cd90a-c92b-1bad-fbec-d1ca6287e826@linux.ibm.com>
Date: Wed, 8 Jun 2022 09:15:46 -0400
From: Matthew Rosato <mjrosato@...ux.ibm.com>
To: Thomas Huth <thuth@...hat.com>, linux-s390@...r.kernel.org
Cc: alex.williamson@...hat.com, cohuck@...hat.com,
schnelle@...ux.ibm.com, farman@...ux.ibm.com, pmorel@...ux.ibm.com,
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oberpar@...ux.ibm.com, freude@...ux.ibm.com, pasic@...ux.ibm.com,
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Subject: Re: [PATCH v9 10/21] vfio/pci: introduce CONFIG_VFIO_PCI_ZDEV_KVM
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@...ux.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.
>
> 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
>
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