kernel/linux.git/Documentation/admin-guide, branch v5.10.261

cpufreq: Documentation: fix conservative governor freq_step description

2026-07-24T13:48:59+00:00

[ Upstream commit 03120e1425262c7d11f93362a88e579a1720390b ] The conservative governor documentation incorrectly states that setting freq_step to 0 will use the default 5% frequency step. In reality, since at least commit 8e677ce83bf4 ("[CPUFREQ] conservative: fixup governor to function more like ondemand logic"), freq_step=0 has always caused the governor to skip frequency updates entirely. Correct the documentation to reflect the actual behavior: freq_step=0 disables frequency changes by the governor entirely. Fixes: 2a0e49279850 ("cpufreq: User/admin documentation update and consolidation") Signed-off-by: Pengjie Zhang Reviewed-by: Zhongqiu Han [ rjw: Subject adjustment ] Link: https://patch.msgid.link/20260603055635.1549943-1-zhangpengjie2@huawei.com Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

cpufreq: Documentation: fix sampling_down_factor range

2026-07-24T13:48:56+00:00

[ Upstream commit 85524e651d20944399322d46fb97960337831d43 ] The ondemand governor implementation accepts sampling_down_factor values from 1 to 100000 via MAX_SAMPLING_DOWN_FACTOR, but the documentation in admin-guide/pm/cpufreq.rst still says the valid range is 1 to 100. Update the documentation to match the actual code. Fixes: 2a0e49279850 ("cpufreq: User/admin documentation update and consolidation") Reviewed-by: Zhongqiu Han Signed-off-by: Pengjie Zhang Link: https://patch.msgid.link/20260518133457.2408463-1-zhangpengjie2@huawei.com Signed-off-by: Rafael J. Wysocki Signed-off-by: Sasha Levin

fs: Add 'initramfs_options' to set initramfs mount options

2025-10-29T13:01:14+00:00

[ Upstream commit 278033a225e13ec21900f0a92b8351658f5377f2 ] When CONFIG_TMPFS is enabled, the initial root filesystem is a tmpfs. By default, a tmpfs mount is limited to using 50% of the available RAM for its content. This can be problematic in memory-constrained environments, particularly during a kdump capture. In a kdump scenario, the capture kernel boots with a limited amount of memory specified by the 'crashkernel' parameter. If the initramfs is large, it may fail to unpack into the tmpfs rootfs due to insufficient space. This is because to get X MB of usable space in tmpfs, 2*X MB of memory must be available for the mount. This leads to an OOM failure during the early boot process, preventing a successful crash dump. This patch introduces a new kernel command-line parameter, initramfs_options, which allows passing specific mount options directly to the rootfs when it is first mounted. This gives users control over the rootfs behavior. For example, a user can now specify initramfs_options=size=75% to allow the tmpfs to use up to 75% of the available memory. This can significantly reduce the memory pressure for kdump. Consider a practical example: To unpack a 48MB initramfs, the tmpfs needs 48MB of usable space. With the default 50% limit, this requires a memory pool of 96MB to be available for the tmpfs mount. The total memory requirement is therefore approximately: 16MB (vmlinuz) + 48MB (loaded initramfs) + 48MB (unpacked kernel) + 96MB (for tmpfs) + 12MB (runtime overhead) ≈ 220MB. By using initramfs_options=size=75%, the memory pool required for the 48MB tmpfs is reduced to 48MB / 0.75 = 64MB. This reduces the total memory requirement by 32MB (96MB - 64MB), allowing the kdump to succeed with a smaller crashkernel size, such as 192MB. An alternative approach of reusing the existing rootflags parameter was considered. However, a new, dedicated initramfs_options parameter was chosen to avoid altering the current behavior of rootflags (which applies to the final root filesystem) and to prevent any potential regressions. Also add documentation for the new kernel parameter "initramfs_options" This approach is inspired by prior discussions and patches on the topic. Ref: https://www.lightofdawn.org/blog/?viewDetailed=00128 Ref: https://landley.net/notes-2015.html#01-01-2015 Ref: https://lkml.org/lkml/2021/6/29/783 Ref: https://www.kernel.org/doc/html/latest/filesystems/ramfs-rootfs-initramfs.html#what-is-rootfs Signed-off-by: Lichen Liu Link: https://lore.kernel.org/20250815121459.3391223-1-lichliu@redhat.com Tested-by: Rob Landley Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin

x86/vmscape: Enable the mitigation

2025-09-11T15:16:06+00:00

commit 556c1ad666ad90c50ec8fccb930dd5046cfbecfb upstream. Enable the previously added mitigation for VMscape. Add the cmdline vmscape={off|ibpb|force} and sysfs reporting. Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Reviewed-by: Dave Hansen Signed-off-by: Amit Shah Signed-off-by: Greg Kroah-Hartman

Documentation/hw-vuln: Add VMSCAPE documentation

2025-09-11T15:16:06+00:00

commit 9969779d0803f5dcd4460ae7aca2bc3fd91bff12 upstream. VMSCAPE is a vulnerability that may allow a guest to influence the branch prediction in host userspace, particularly affecting hypervisors like QEMU. Add the documentation. Signed-off-by: Pawan Gupta Signed-off-by: Dave Hansen Reviewed-by: Borislav Petkov (AMD) Reviewed-by: Dave Hansen Signed-off-by: Amit Shah Signed-off-by: Greg Kroah-Hartman

x86/bugs: Add a Transient Scheduler Attacks mitigation

2025-07-17T16:28:00+00:00

From: "Borislav Petkov (AMD)" Commit d8010d4ba43e9f790925375a7de100604a5e2dba upstream. Add the required features detection glue to bugs.c et all in order to support the TSA mitigation. Co-developed-by: Kim Phillips Signed-off-by: Kim Phillips Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman

x86/bugs: Rename MDS machinery to something more generic

2025-07-17T16:28:00+00:00

From: "Borislav Petkov (AMD)" Commit f9af88a3d384c8b55beb5dc5483e5da0135fadbd upstream. It will be used by other x86 mitigations. No functional changes. Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman

x86/its: Add "vmexit" option to skip mitigation on some CPUs

2025-07-17T16:27:56+00:00

commit 2665281a07e19550944e8354a2024635a7b2714a upstream. Ice Lake generation CPUs are not affected by guest/host isolation part of ITS. If a user is only concerned about KVM guests, they can now choose a new cmdline option "vmexit" that will not deploy the ITS mitigation when CPU is not affected by guest/host isolation. This saves the performance overhead of ITS mitigation on Ice Lake gen CPUs. When "vmexit" option selected, if the CPU is affected by ITS guest/host isolation, the default ITS mitigation is deployed. Signed-off-by: Dave Hansen Reviewed-by: Josh Poimboeuf Reviewed-by: Alexandre Chartre Signed-off-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman

x86/its: Enable Indirect Target Selection mitigation

2025-07-17T16:27:55+00:00

commit f4818881c47fd91fcb6d62373c57c7844e3de1c0 upstream. Indirect Target Selection (ITS) is a bug in some pre-ADL Intel CPUs with eIBRS. It affects prediction of indirect branch and RETs in the lower half of cacheline. Due to ITS such branches may get wrongly predicted to a target of (direct or indirect) branch that is located in the upper half of the cacheline. Scope of impact =============== Guest/host isolation -------------------- When eIBRS is used for guest/host isolation, the indirect branches in the VMM may still be predicted with targets corresponding to branches in the guest. Intra-mode ---------- cBPF or other native gadgets can be used for intra-mode training and disclosure using ITS. User/kernel isolation --------------------- When eIBRS is enabled user/kernel isolation is not impacted. Indirect Branch Prediction Barrier (IBPB) ----------------------------------------- After an IBPB, indirect branches may be predicted with targets corresponding to direct branches which were executed prior to IBPB. This is mitigated by a microcode update. Add cmdline parameter indirect_target_selection=off|on|force to control the mitigation to relocate the affected branches to an ITS-safe thunk i.e. located in the upper half of cacheline. Also add the sysfs reporting. When retpoline mitigation is deployed, ITS safe-thunks are not needed, because retpoline sequence is already ITS-safe. Similarly, when call depth tracking (CDT) mitigation is deployed (retbleed=stuff), ITS safe return thunk is not used, as CDT prevents RSB-underflow. To not overcomplicate things, ITS mitigation is not supported with spectre-v2 lfence;jmp mitigation. Moreover, it is less practical to deploy lfence;jmp mitigation on ITS affected parts anyways. Signed-off-by: Dave Hansen Reviewed-by: Josh Poimboeuf Reviewed-by: Alexandre Chartre Signed-off-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman

Documentation: x86/bugs/its: Add ITS documentation

2025-07-17T16:27:54+00:00

commit 1ac116ce6468670eeda39345a5585df308243dca upstream. Add the admin-guide for Indirect Target Selection (ITS). Signed-off-by: Dave Hansen Reviewed-by: Josh Poimboeuf Reviewed-by: Alexandre Chartre Signed-off-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman