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Wed, 7 Oct 2026 13:59:34 +0000 (GMT) Received: from Mac.ibm.com (unknown [9.61.253.231]) by smtpav06.wdc07v.mail.ibm.com (Postfix) with ESMTP; Wed, 7 Oct 2026 13:59:34 +0000 (GMT) From: Omar Elghoul To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: oelghoul@linux.ibm.com, hca@linux.ibm.com, gor@linux.ibm.com, agordeev@linux.ibm.com, borntraeger@linux.ibm.com, svens@linux.ibm.com, schnelle@linux.ibm.com, mjrosato@linux.ibm.com, alifm@linux.ibm.com, farman@linux.ibm.com, gbayer@linux.ibm.com, pasic@linux.ibm.com, alex@shazbot.org, frankja@linux.ibm.com, imbrenda@linux.ibm.com Subject: [PATCH v9 0/4] vfio-pci/zdev: Improved zPCI Function Measurement Support Date: Wed, 7 Oct 2026 09:59:22 -0400 Message-ID: <20261007135926.82935-1-oelghoul@linux.ibm.com> X-Mailer: git-send-email 2.56.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: rz71JCTSCqC9iFeGEbRKjYKMLVbo72Dh X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA3MDA1NCBTYWx0ZWRfX8Qhd/oKF2QdU wyMouDs1LSc93YDp2RGqU35s4X3C4BeLFUjg/CSE+2nA9ZXt6KEbuusFQ0PuoG/iganGP9622PL alYet0hq5ra6fET8mobqUOj5z0FEq78= X-Proofpoint-GUID: rz71JCTSCqC9iFeGEbRKjYKMLVbo72Dh X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA3MDA1NCBTYWx0ZWRfX9fbPxSAepI2+ l74n5f/9OUuKE9XYAwtudlngnciiUQlx5QlrnU/S0GJ6YGOJMUNqUgu9cSfFpYsjVkG0hmGBCyp yHYoT34j3yHQRae6j3/obr6yiw36xXo463cKiyGAK/vI4XA1396dvicnPnmwDdY3j6wPaC2cNQI lehXGZ5UiAs5r75TyE1THKSBIsqEd1S7oJDbAkvBqqq3PhQmMCxLn8YMLcET0yH7i8RAl8jUk7I DSIK8AtdK9M8Sj2s5SRJjadEZg/M3TbFAW/WAFVmt0FJAOisg0FG48INdIZu5031jnfV6xofXvG GZlm3m7ju1CW51zSiwh5Yyuagx56nW4oAfHoJIAW9n6+ST6lOWxX2Tr/04m61s1qNwGsNEtNl3h RBM1/CHZjGmSOaBCxCDUopqI5R/7vYVLinMsBQj4yqHzrAc8KPslIY+QeeN2ZOl7H/oRUI86h4P nEsl1Xost9Xv1YYdsRQ== X-Authority-Analysis: v=2.4 cv=fM2sTpae c=1 sm=1 tr=0 ts=6ac6504c cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=5osLMtGHjg6MEC5_PQ4A:9 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-07_04,2026-10-06_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 bulkscore=0 priorityscore=1501 spamscore=0 lowpriorityscore=0 phishscore=0 adultscore=0 malwarescore=0 clxscore=1015 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2610070054 Hi, This patch series improves support for function measurement for zPCI passthrough devices on s390. Changelog ========= v8 -> v9: * Patch 2/4: - Remove the intermediate disable step from zpci_fmb_reenable_device() for more uniform semantics - Rename fmb_enabled to fmb_requested with the intent of tracking the desired status of FMB enablement - Make zpci_fmb_enable_device() delegate to zpci_fmb_reenable_device() * Patch 4/4: - Set fmb_requested when the user enables measurement v7 -> v8: * Patch 2/4: - Replace the fmb_enabled bitfield in struct zpci_dev with a dedicated bool to avoid future tearing bugs - Rewrite commit message for a more natural flow * Patch 4/4: - Replace mutex_lock/unlock() in vfio_pci_zdev_feature_fmb_read() with a scoped_guard() v6 -> v7: * Patch 2/4: - Don't re-enable FMB if it wasn't already enabled v5 -> v6: * Patch 2/4: - Rework the FMB re-enablement code to reuse the same buffer again - Make the FMB buffer persistent once allocated for as long as the device's lifetime to accommodate an architectural quirk * Patch 4/4: - Update the liveness check to use the new FMB enabled bool v4 -> v5: * Typo in the cover letter * Swap the ordering of patches 3/4 and 4/4 to ease merging (i.e., to ensure the three s390 patches are ordered before the VFIO patch) * Patch 2/4: - Drop the refactor of zpci_fmb_enable_device() and the separation of zpci_fmb_clear_iommu_ctrs() and zpci_fmb_do_enable() - Allocate a new buffer in zpci_fmb_reenable_device() rather than reusing the same buffer to avoid firmware edge cases * Patch 3/4 (previously 4/4): - Avoid reading from userspace while holding kzdev_lock unnecessarily * Patch 4/4 (previously 3/4): - Drop allowing usercopy of the FMB when initializing the kmem_cache - Avoid copying to userspace while holding fmb_lock unnecessarily - Restore the FMB bounce buffer to achieve this one - Clarify uAPI documentation and ensure it accurately describes the behavior of the VFIO features v3 -> v4: * Patch 2/4: - Replace mutex_lock/unlock in zpci_reenable_device() with a guard * Patch 3/4: - Allow usercopy of the FMB when initializing its kmem_cache - Move the guard in vfio_pci_zdev_feature_fmb_enable() lower to only protect the FMB - Ensure vfio_pci_zdev_feature_fmb_enable() fails on double-enable for consistency with the documentation - Eliminate the bounce buffer in vfio_pci_zdev_feature_fmb_read() - Replace the void pointer with __aligned_u64 in the FMB read uAPI structure v2 -> v3: * Patch 1/4 (new patch): - Fix race conditions in pcibios_enable/disable_device() with regard to the FMB enable/disable - Assert that fmb_lock is held within zpci_fmb_enable_device() and zpci_fmb_disable_device() * Patch 2/4 (previously 1/3): - Move the FMB enable logic into a static function zpci_fmb_do_enable() to reduce code duplication between zpci_fmb_enable_device() and zpci_fmb_reenable_device() - Reword commit message to use the imperative voice more consistently * Patch 3/4 (previously 2/3): - Split the previous VFIO feature into a SET-only and a GET-only feature for enabling/disabling and reading the FMB respectively - Remove FMB definitions from the VFIO uAPI and instead treat it as an opaque structure * Patch 4/4 (previously 3/3): - Clarify goto label name to reduce misunderstandings 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 (4): s390/pci: Hold fmb_lock when enabling or disabling PCI devices s390/pci: Reuse FMB buffer and preserve state in device re-enablement s390/pci: Fence FMB enable/disable via debugfs for passthrough devices vfio-pci/zdev: Add VFIO FMB device features arch/s390/include/asm/pci.h | 2 + arch/s390/pci/pci.c | 108 ++++++++++++++++++++----------- arch/s390/pci/pci_debug.c | 11 +++- drivers/vfio/pci/vfio_pci_core.c | 4 ++ drivers/vfio/pci/vfio_pci_priv.h | 18 ++++++ drivers/vfio/pci/vfio_pci_zdev.c | 60 +++++++++++++++++ include/uapi/linux/vfio.h | 29 +++++++++ 7 files changed, 195 insertions(+), 37 deletions(-) -- 2.56.0