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Tue, 3 Nov 2026 15:01:18 +0000 (GMT) Received: from Mac.ibm.com (unknown [9.61.243.67]) by smtpav03.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 3 Nov 2026 15:01:17 +0000 (GMT) From: Omar Elghoul To: linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: 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 v12 0/5] vfio-pci/zdev: Improved zPCI Function Measurement Support Date: Tue, 3 Nov 2026 10:01:09 -0500 Message-ID: <20261103150114.68873-1-oelghoul@linux.ibm.com> X-Mailer: git-send-email 2.56.0 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: EaCAseHP6r29Qn9Pg-YVwq9BkPmXl7Me X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAzMDA1OCBTYWx0ZWRfX1xoZZhZh2moC aA9JCz77u2+r7SueaVqT2m7hRUkdR31hFHPQlUVTgh9rcmABpYdrV4pSeuzzZYWvSDGiHkeJH2U /yeUcBdX70OfqINA1jQZzjeq4cr9Az3lUzxQeg0ZgpvpQhWV/6FmkNqhTFiUwOBljA8JOhi/9qC tQ1TTQFlQGc23WVpClQzCVTRh2aWNZP+QJtPv1XcqrYeBJp+HgP4UX//Xa/lChOeRMbNiEd3bHf 1AIzX55qaeMM1hT5jerTVSY1afrXQv23oSmKgJdv1XJ4C8UTVRBhauVVmSrjHHgwohgqOHeQBVg pxFx4TOqp2r4wzzymPlHy0zQa7X+BUMoEtfJk4J5D+niDWCqYKOwexkCp7IIAlEF+2awYjhHcJM k2S6p4Tujnkg89Fl5qBlZnphKHnkvhqA0poEDDLI8RpeaiHOkLY+wjDlyOyiU792DHFmmEyRiW0 ymwclzc7R/e87+O+Pug== X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAzMDA1OCBTYWx0ZWRfX47oM5mBnE+0K MsnZghMXfppbiwpN2RQ7skbU79k/PoIkEVQacbXP63M5EX2176xi1rtRAbE6HbZwS9cRT6p9eii n4EAcATS8wYwer667/+eSvwK8t+gHTM= X-Authority-Analysis: v=2.4 cv=QK391QLL c=1 sm=1 tr=0 ts=6ae9f743 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=4XtsKJ7C2CqOUlitrrcA:9 X-Proofpoint-ORIG-GUID: EaCAseHP6r29Qn9Pg-YVwq9BkPmXl7Me X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-03_03,2026-11-03_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 impostorscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611030058 Hi, This patch series improves support for function measurement for zPCI passthrough devices on s390. Changelog ========= v11 -> v12: * Patch 2/5: - Replace the statistics_on bool with a bitfield * Patch 3/5: - Add the fmb_enabled bitfield to struct zpci_dev to track the actual FMB enablement - Replace the kmem_cache allocator with kzalloc/kfree after learning it guarantees alignment for power-of-two sizes * Patch 5/5: - Use fmb_enabled as the FMB liveness check v10 -> v11: * Patches 2/5 and 3/5: - Swap their ordering within the series - Set/unset statistics_on after an enable/disable succeeds instead of before * Patch 5/5: - On FMB re-enable, use an intermediate request-off step instead of directly touching the device state v9 -> v10: * Patches 2/5 and 3/5: - Split the old 2/4 into two patches; the new patch 2/5 reuses one FMB buffer per device, and 3/5 improves FMB state management - Rework FMB management functions to decouple requesting enablement or disablement from managing the user's intended state - Preserve measurement state in pcibios_enable_device() 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 (5): s390/pci: Hold fmb_lock when enabling or disabling PCI devices s390/pci: Improve function measurement state management s390/pci: Improve FMB memory management 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 | 8 +- arch/s390/pci/pci.c | 121 +++++++++++++++++++++++-------- arch/s390/pci/pci_debug.c | 15 +++- drivers/vfio/pci/vfio_pci_core.c | 4 + drivers/vfio/pci/vfio_pci_priv.h | 18 +++++ drivers/vfio/pci/vfio_pci_zdev.c | 64 ++++++++++++++++ include/uapi/linux/vfio.h | 30 ++++++++ 7 files changed, 224 insertions(+), 36 deletions(-) -- 2.56.0