February 2026 - Devel - libvirt List Archives

[RFC PATCH] Prioritise and validate cgroup2 canonical mount on /sys/fs/cgroup
by Rogério Vinhal Nunes 03 Feb '26

03 Feb '26

Hey folks, we've gotten an issue with how libvirt is currently detecting the cgroup2 mounts. Basically we expose cgroup2 mounts in a container from the host-level and libvirt was selecting that instead of the container-level mount, which uses the canonical path. The current logic basically iterate on the mounts until it finds a cgroup2 mount and uses that. If there's multiple, it will override until the last one is read, which is not very safe. I've cut a quick patch that should: 1. Validate that the mount is actually an existing directory in the context 2. Prefer the canonical mount (/sys/fs/cgroup) if it's available 3. only override it once, so it will not go through lists of mounts overriding up to the end I'm happy to get some feedback here especially on step 3 as I'm not very sure how we should proceed on non-canonical situations or if we should at all. Maybe the best solution is to just use the canonical path? From 4a0bf5c5b1e1cd4e0393981a25e1407d29beb43e Mon Sep 17 00:00:00 2001 From: Rogerio Vinhal Nunes <rogervn(a)meta.com> Date: Mon, 2 Feb 2026 19:24:52 +0000 Subject: [PATCH] Preferred /sys/fs/cgroup as a canonical mount but also verifies if the mount is an existing directory in the namespace. The reason for this is preventing that mounts that are not visible in the container namespace or additional cgroupv2 mounts to share host context might be incorrectly taken as targets here. --- src/util/vircgroupv2.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/src/util/vircgroupv2.c b/src/util/vircgroupv2.c index eaf5ae98f6..aa8c950691 100644 --- a/src/util/vircgroupv2.c +++ b/src/util/vircgroupv2.c @@ -23,6 +23,7 @@ #ifdef __linux__ # include <mntent.h> # include <sys/mount.h> +# include <sys/stat.h> #endif /* __linux__ */ #include "internal.h" @@ -46,6 +47,8 @@ VIR_LOG_INIT("util.cgroup"); #define VIR_FROM_THIS VIR_FROM_CGROUP +#define VIR_CGROUP_SYSFS_MOUNT "/sys/fs/cgroup" + VIR_ENUM_DECL(virCgroupV2Controller); VIR_ENUM_IMPL(virCgroupV2Controller, VIR_CGROUP_CONTROLLER_LAST, @@ -173,12 +176,26 @@ virCgroupV2DetectMounts(virCgroup *group, const char *mntOpts G_GNUC_UNUSED, const char *mntDir) { + struct stat sb; + if (STRNEQ(mntType, "cgroup2")) return 0; - VIR_FREE(group->unified.mountPoint); + if (stat(mntDir, &sb) < 0 || !S_ISDIR(sb.st_mode)) { + VIR_DEBUG("Skipping non-directory cgroup2 mount: %s", mntDir); + return 0; + } + + /* Always prefer /sys/fs/cgroup as the canonical mount point. + * If we already have /sys/fs/cgroup, don't override it. + * Otherwise, use the first valid directory we find as fallback. */ + if (STREQ(mntDir, VIR_CGROUP_SYSFS_MOUNT)) { + VIR_FREE(group->unified.mountPoint); + group->unified.mountPoint = g_strdup(mntDir); + } else if (!group->unified.mountPoint) { + group->unified.mountPoint = g_strdup(mntDir); + } - group->unified.mountPoint = g_strdup(mntDir); return 0; } -- 2.52.0

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[RFC PATCH v4 0/7] riscv: add initial sdext support
by Chao Liu 02 Feb '26

02 Feb '26

Hi, Per Daniel's review feedback, this v4 series is based on Alistair's riscv-to-apply.next branch [3]. It depends on patches 1-5 of Max Chou's "Add Zvfbfa extension support" v2 series (not included; apply them first) [2]. It is based on RISC-V Debug Specification 1.0 [1]. It introduces the sdext/sdtrig config bits, DCSR/DPC/DSCRATCH state, Debug Mode enter/leave helpers, DRET, EBREAK entry, single-step, and trigger action=debug mode. To reduce review load, this series focuses on the Sdext features first. The Debug Module (DM) and related flows will follow in a later series. Changes in v4: - Fixed linux-user build errors: moved debug_mode/dcsr/dpc/dscratch fields inside #ifndef CONFIG_USER_ONLY block in cpu.h, and wrapped all code using these fields with proper guards. (Daniel) - Updated dependency from single patch (patch 5 only) to patches 1-5 of Max Chou's "Add Zvfbfa extension support" v2 series to avoid compilation errors. Changes in v3: - Rebase onto Alistair's riscv-to-apply.next branch. - Depend on Max Chou's patch "target/riscv: Use the tb->cs_bqse as the extend tb flags." (not included; apply it first) [2]. - Patch 2: default sdext to false in riscv_cpu_extensions[]. Changes in v2: - Drop the RHCT expected AML update from this series. - Replace the split sdext/sdtrig config bits patch with deprecating the 'debug' CPU property. - Rebase and update patch subjects to target/riscv prefix. Changes in v1: - Debug Mode entry/exit updates DCSR/DPC and restores execution via DRET. - EBREAK honors DCSR ebreak bits and enters Debug Mode when enabled. - Single-step uses DCSR.STEP with a TB flag and a helper at TB exit. It references Max Chou's patch "target/riscv: Use the tb->cs_bqse as the extend tb flags." [2]. - Sdtrig supports action=debug mode for mcontrol/mcontrol6 and reports inst-count triggers in tinfo. Differences vs Debug Spec (known gaps): - No Debug Module (no DMI, dmcontrol/dmstatus, haltreq/resumereq). - No debug ROM, program buffer, abstract commands, or SBA. - Resume is modeled by leaving Debug Mode at cpu_exec_enter. - Step/exception ordering is simplified: if the stepped instruction traps, the normal exception is taken and Debug Mode is not forced. - Several DCSR fields are not fully modeled (stopcount/stoptime, etc). Roadmap (next stage, DM focus): 1) Add a DM core with DMI access and hart state tracking. 2) Implement halt/resume handshake and move Debug Mode transitions under DM control. 3) Add debug ROM, program buffer, and abstract commands for GPR/CSR and memory access. 4) Add SBA if required by tooling. 5) Tighten ordering rules for step/exception/trigger priorities. References: [1] https://github.com/riscv/riscv-debug-spec/releases/tag/1.0 [2] https://lore.kernel.org/qemu-devel/20260108132631.9429-1-max.chou@sifive.co… [3] https://github.com/alistair23/qemu/tree/riscv-to-apply.next Thanks, Chao Chao Liu (6): target/riscv: add sdext debug CSRs state target/riscv: add sdext Debug Mode helpers target/riscv: add dret instruction target/riscv: add sdext enter Debug Mode on ebreak target/riscv: add sdext single-step support target/riscv: add sdtrig trigger action=debug mode Daniel Henrique Barboza (1): target/riscv: deprecate 'debug' CPU property docs/about/deprecated.rst | 7 + include/exec/translation-block.h | 4 +- target/riscv/cpu.c | 62 ++++++++- target/riscv/cpu.h | 9 ++ target/riscv/cpu_bits.h | 33 +++++ target/riscv/cpu_cfg_fields.h.inc | 3 +- target/riscv/cpu_helper.c | 90 ++++++++++++ target/riscv/csr.c | 128 +++++++++++++++++- target/riscv/debug.c | 58 +++++++- target/riscv/helper.h | 3 + target/riscv/insn32.decode | 1 + .../riscv/insn_trans/trans_privileged.c.inc | 24 ++++ target/riscv/machine.c | 44 ++++-- target/riscv/op_helper.c | 70 ++++++++++ target/riscv/tcg/tcg-cpu.c | 21 ++- target/riscv/translate.c | 16 ++- 16 files changed, 548 insertions(+), 25 deletions(-) -- 2.52.0

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Qemu pause-before-switchover and libvirt live migration
by Rogério Vinhal Nunes 02 Feb '26

02 Feb '26

Hello, I’m looking into the libvirt hooks that are available to make use of during a live migration, but there's only hooks on migration begin and migration end. On qemu directly I’m able to use pause-before-switchover migration capability to run a custom operation just before it moves to the destination, but within libvirt it seems that while this is leveraged internally, it’s not currently exposed to the client in a way I can use. Does anyone have any suggestions on how I could expose this to the client in a generic and sensible way? Thanks, Rogerio

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[PATCH v6 0/7] qemu: Implement support for iommufd
by Nathan Chen 02 Feb '26

02 Feb '26

Hi, This is a follow up to the fifth patch series [0] for using iommufd to propagate DMA mappings to the kernel for VM-assigned host devices in a qemu VM. We add a new 'iommufd' attribute for hostdev devices to be associated with the iommufd object. For instance, specifying the iommufd object and associated hostdev in a VM definition: <devices> ... <hostdev mode='subsystem' type='pci' managed='no'> <driver iommufd='yes'/> <source> <address domain='0x0009' bus='0x01' slot='0x00' function='0x0'/> </source> <address type='pci' domain='0x0000' bus='0x15' slot='0x00' function='0x0'/> </hostdev> <hostdev mode='subsystem' type='pci' managed='no'> <driver iommufd='yes'/> <source> <address domain='0x0019' bus='0x01' slot='0x00' function='0x0'/> </source> <address type='pci' domain='0x0000' bus='0x16' slot='0x00' function='0x0'/> </hostdev> ... </devices> This would get translated to a qemu command line with the arguments below. Note that libvirt will open the /dev/iommu and VFIO cdev, passing the associated fd number to qemu: -object '{"qom-type":"iommufd","id":"iommufd0","fd":"24"}' \ -device '{"driver":"vfio-pci","host":"0009:01:00.0","id":"hostdev0","iommufd":"iommufd0","fd":"22","bus":"pci.21","addr":"0x0"}' \ -device '{"driver":"vfio-pci","host":"0019:01:00.0","id":"hostdev1","iommufd":"iommufd0","fd":"25","bus":"pci.22","addr":"0x0"}' \ Changes from v5: - Updated documentation to point to 12.1.0 (QEMU and KVM only) - Move define and VIR_LOG_INIT out of #ifdef __linux__ block in viriommufd.h - Remove unneeded virPCIDeviceFree() from AppArmorSetSecurityHostdevLabel - Always error out if per-process accounting failed Changes from v4: - Move qemuProcessOpenVfioFds() to qemu_process.h in patch 4/7 - Add `linux/iommufd.h` into headers list in the meson.build file - Correct viriommufd.c pre-processor definition indentations - Restore call to virIOMMUFDSetRLimitMode() in patch 5/7 - Fix indentations for various print function calls - Move the qemuProcessOpenVfioFds() call to qemuProcessPrepareHost() - Make qemuProcessOpenVfioFds() static - Remove unnecessary formatting and comment in virPCIDeviceGetVfioPath() - Clean up namespace and cgroup changes with conditional check for iommufd - Remove virIOMMUFDSupported() - Fix seclabel return logic - In Apparmor seclabel logic, use g_autoptr for virPCIDevice pointer Changes from v3: - Resolved issue from v2 where stale FD from previous VM boot was in use - Remove second approach for retrieving VFIO device path in virPCIDeviceGetVfioPath() - Resolve broken build of libvirt on non-Linux platforms - Conditionally define iommufd headers and use system headers where possible - Add non-fatal handling + warning print for EPERM for the IOMMU_OPTION_RLIMIT_MODE ioctl - Replace references to /dev/iommu with VIR_IOMMU_DEV_PATH - Implement virIOMMUFDSupported(void) to check for existence of /dev/iommu on host - Include tests for multiple hostdevs Changes from v2: - Set per-process memory accounting mode for iommufd - Separated out formatting of iommufd object from qemuBuildHostdevCommandLine - Placed hostdev private data implementation in a separate commit - Allocate hostdev private data unconditionally - Compare FDs against -1 - Integrated callback function in virQEMUDriverPrivateDataCallbacks for qemuDomainHostdevPrivateNew - Dropped qemuProcessCloseVfioFds - Addressed other feedback from v2 (formatting, includes, etc.) - Revised seclabel logic to be device-specific for AppArmor and to allow paths for SELinux/DAC This series is on Github: https://github.com/NathanChenNVIDIA/libvirt/commits/iommufd-v6-01-26 Thanks, Nathan [0] https://lists.libvirt.org/archives/list/devel@lists.libvirt.org/thread/GKSD… Nathan Chen (7): qemu: Implement support for associating iommufd to hostdev qemu: Introduce privateData for hostdevs qemu: Support per-process memory accounting for iommufd qemu: open VFIO FDs from libvirt backend qemu: open iommufd FD from libvirt backend qemu: Update Cgroup, namespace, and seclabel for iommufd tests: qemuxmlconfdata: provide iommufd sample XML and CLI args docs/formatdomain.rst | 6 + meson.build | 1 + po/POTFILES | 1 + src/bhyve/bhyve_parse_command.c | 2 +- src/conf/device_conf.c | 11 ++ src/conf/device_conf.h | 1 + src/conf/domain_conf.c | 13 +- src/conf/domain_conf.h | 5 +- src/conf/schemas/basictypes.rng | 5 + src/libvirt_private.syms | 4 + src/libxl/xen_common.c | 2 +- src/libxl/xen_xl.c | 2 +- src/lxc/lxc_native.c | 2 +- src/qemu/qemu_cgroup.c | 3 + src/qemu/qemu_command.c | 76 +++++++++++ src/qemu/qemu_domain.c | 41 ++++++ src/qemu/qemu_domain.h | 17 +++ src/qemu/qemu_namespace.c | 3 + src/qemu/qemu_process.c | 121 ++++++++++++++++++ src/security/security_apparmor.c | 28 ++-- src/security/security_dac.c | 49 +++++-- src/security/security_selinux.c | 47 +++++-- src/security/virt-aa-helper.c | 33 ++++- src/util/meson.build | 1 + src/util/viriommufd.c | 111 ++++++++++++++++ src/util/viriommufd.h | 25 ++++ src/util/virpci.c | 39 ++++++ src/util/virpci.h | 2 + src/vbox/vbox_common.c | 2 +- .../iommufd-q35.x86_64-latest.args | 41 ++++++ .../iommufd-q35.x86_64-latest.xml | 60 +++++++++ tests/qemuxmlconfdata/iommufd-q35.xml | 38 ++++++ ...fd-virt-pci-bus-single.aarch64-latest.args | 32 +++++ ...ufd-virt-pci-bus-single.aarch64-latest.xml | 31 +++++ .../iommufd-virt-pci-bus-single.xml | 22 ++++ .../iommufd-virt.aarch64-latest.args | 36 ++++++ .../iommufd-virt.aarch64-latest.xml | 53 ++++++++ tests/qemuxmlconfdata/iommufd-virt.xml | 29 +++++ .../iommufd.x86_64-latest.args | 35 +++++ .../qemuxmlconfdata/iommufd.x86_64-latest.xml | 38 ++++++ tests/qemuxmlconfdata/iommufd.xml | 30 +++++ tests/qemuxmlconftest.c | 34 +++++ tests/virhostdevtest.c | 2 +- 43 files changed, 1090 insertions(+), 44 deletions(-) create mode 100644 src/util/viriommufd.c create mode 100644 src/util/viriommufd.h create mode 100644 tests/qemuxmlconfdata/iommufd-q35.x86_64-latest.args create mode 100644 tests/qemuxmlconfdata/iommufd-q35.x86_64-latest.xml create mode 100644 tests/qemuxmlconfdata/iommufd-q35.xml create mode 100644 tests/qemuxmlconfdata/iommufd-virt-pci-bus-single.aarch64-latest.args create mode 100644 tests/qemuxmlconfdata/iommufd-virt-pci-bus-single.aarch64-latest.xml create mode 100644 tests/qemuxmlconfdata/iommufd-virt-pci-bus-single.xml create mode 100644 tests/qemuxmlconfdata/iommufd-virt.aarch64-latest.args create mode 100644 tests/qemuxmlconfdata/iommufd-virt.aarch64-latest.xml create mode 100644 tests/qemuxmlconfdata/iommufd-virt.xml create mode 100644 tests/qemuxmlconfdata/iommufd.x86_64-latest.args create mode 100644 tests/qemuxmlconfdata/iommufd.x86_64-latest.xml create mode 100644 tests/qemuxmlconfdata/iommufd.xml -- 2.43.0

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[PATCH 0/2] target/arm: Deprecate '-cpu any'
by Philippe Mathieu-Daudé 01 Feb '26

01 Feb '26

Arm '-cpu any' is aliased to '-cpu max' since more than 5 years. Deprecate the former in preparation of removal. Philippe Mathieu-Daudé (2): target/arm: Remove dead code target/arm: Deprecate '-cpu any' (remplaced by '-cpu max') docs/about/deprecated.rst | 8 ++++++++ target/arm/cpu.c | 1 + target/arm/tcg/cpu32.c | 3 --- 3 files changed, 9 insertions(+), 3 deletions(-) -- 2.52.0

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