Re: [PATCH v2 0/3] vfio-pci/zdev: Improved zPCI Function Measurement Support

[Omar Elghoul <oelghoul@linux.ibm.com>]

Hi,

Gently pinging the series in case it has fallen out of your radars.

Thanks.

On 5/19/26 6:42 PM, Omar Elghoul wrote:
> Hi,
>
> This patch series improves support for function measurement for zPCI
> passthrough devices on s390x.
>
> Changelog
> =========
> v1 -> v2:
> * Patch 1/3:
>    - Address a possible race condition in zpci_reenable_device() caused by
>      calling zpci_fmb_reenable_device() without holding fmb_lock
>    - Assert that fmb_lock is held within zpci_fmb_reenable_device()
>
> * Patch 3/3:
>    - Address a possible race condition in pci_perf_seq_write() caused by
>      consuming zdev->kzdev without holding kzdev_lock
>
> Motivation
> ==========
> The firmware on s390x machines allows for tracking a variety of statistics
> relating to zPCI devices in a function measurement block (FMB). However,
> the kernel currently lacks a structured mechanism of sharing this
> information with userspace, beyond /sys/kernel/debug/pci/ID/statistics.
> This can lead to shortcomings when running a guest on KVM with PCI
> passthrough devices, as QEMU is unable to provide an accurate FMB snapshot
> to the guest.
>
> Proposal
> ========
> We propose adding a new VFIO device feature to zPCI passthrough devices,
> allowing userspace programs to read the latest FMB snapshot as it is
> written by the firmware. We ensure that function measurement enablement is
> preserved across device resets on the host. Furthermore, we guard against
> host tampering with the FMB via sysfs when the zPCI device is in
> passthrough to protect the VM's state.
>
> I'd appreciate some feedback on these patches.
>
> Thanks in advance.
>
> Omar Elghoul (3):
>    s390/pci: Preserve FMB state in device re-enablement
>    vfio-pci/zdev: Add VFIO FMB device feature
>    s390/pci: Fence FMB enable/disable via sysfs for passthrough devices
>
>   arch/s390/include/asm/pci.h      |  1 +
>   arch/s390/pci/pci.c              | 75 ++++++++++++++++++++++++-------
>   arch/s390/pci/pci_debug.c        | 11 ++++-
>   drivers/vfio/pci/vfio_pci_core.c |  2 +
>   drivers/vfio/pci/vfio_pci_priv.h |  9 ++++
>   drivers/vfio/pci/vfio_pci_zdev.c | 77 ++++++++++++++++++++++++++++++++
>   include/uapi/linux/vfio.h        | 43 ++++++++++++++++++
>   7 files changed, 202 insertions(+), 16 deletions(-)
>