kernel/linux.git/Documentation/admin-guide, branch v5.15.219

cpufreq: Documentation: fix conservative governor freq_step description

2026-07-24T13:51:33+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

2026-07-24T13:51:29+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

2025-10-19T14:21:54+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

2025-09-11T15:17:17+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

2025-09-11T15:17:16+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

2025-07-10T13:57:50+00:00

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

2025-07-10T13:57:50+00:00

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

arm64: spectre: increase parameters that can be used to turn off bhb mitigation individually

2025-06-27T10:05:37+00:00

[ Upstream commit 877ace9eab7de032f954533afd5d1ecd0cf62eaf ] In our environment, it was found that the mitigation BHB has a great impact on the benchmark performance. For example, in the lmbench test, the "process fork && exit" test performance drops by 20%. So it is necessary to have the ability to turn off the mitigation individually through cmdline, thus avoiding having to compile the kernel by adjusting the config. Signed-off-by: Liu Song Acked-by: Catalin Marinas Link: https://lore.kernel.org/r/1661514050-22263-1-git-send-email-liusong@linux.alibaba.com Signed-off-by: Catalin Marinas Signed-off-by: Pu Lehui Signed-off-by: Greg Kroah-Hartman

Revert "x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2" on v6.6 and older

2025-06-27T10:05:33+00:00

This reverts commit 4fc2d289b3cc4cf23ccabe59cf936d1dc49aeda8 which is commit 98fdaeb296f51ef08e727a7cc72e5b5c864c4f4d upstream. commit 7adb96687ce8 ("x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2") depends on commit 72c70f480a70 ("x86/bugs: Add a separate config for Spectre V2"), which introduced MITIGATION_SPECTRE_V2. commit 72c70f480a70 ("x86/bugs: Add a separate config for Spectre V2") never landed in stable tree, thus, stable tree doesn't have MITIGATION_SPECTRE_V2, that said, commit 7adb96687ce8 ("x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2") has no value if the dependecy was not applied. Revert commit 7adb96687ce8 ("x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2") in stable kernel which landed in in 5.4.294, 5.10.238, 5.15.185, 6.1.141 and 6.6.93 stable versions. Cc: David.Kaplan@amd.com Cc: peterz@infradead.org Cc: pawan.kumar.gupta@linux.intel.com Cc: mingo@kernel.org Cc: brad.spengler@opensrcsec.com Cc: stable@vger.kernel.org # 6.6 6.1 5.15 5.10 5.4 Reported-by: Brad Spengler Reported-by: Salvatore Bonaccorso Signed-off-by: Breno Leitao Signed-off-by: Greg Kroah-Hartman

x86/bugs: Make spectre user default depend on MITIGATION_SPECTRE_V2

2025-06-04T12:37:59+00:00

[ Upstream commit 98fdaeb296f51ef08e727a7cc72e5b5c864c4f4d ] Change the default value of spectre v2 in user mode to respect the CONFIG_MITIGATION_SPECTRE_V2 config option. Currently, user mode spectre v2 is set to auto (SPECTRE_V2_USER_CMD_AUTO) by default, even if CONFIG_MITIGATION_SPECTRE_V2 is disabled. Set the spectre_v2 value to auto (SPECTRE_V2_USER_CMD_AUTO) if the Spectre v2 config (CONFIG_MITIGATION_SPECTRE_V2) is enabled, otherwise set the value to none (SPECTRE_V2_USER_CMD_NONE). Important to say the command line argument "spectre_v2_user" overwrites the default value in both cases. When CONFIG_MITIGATION_SPECTRE_V2 is not set, users have the flexibility to opt-in for specific mitigations independently. In this scenario, setting spectre_v2= will not enable spectre_v2_user=, and command line options spectre_v2_user and spectre_v2 are independent when CONFIG_MITIGATION_SPECTRE_V2=n. Signed-off-by: Breno Leitao Signed-off-by: Ingo Molnar Reviewed-by: Pawan Gupta Acked-by: Josh Poimboeuf Cc: Peter Zijlstra Cc: David Kaplan Link: https://lore.kernel.org/r/20241031-x86_bugs_last_v2-v2-2-b7ff1dab840e@debian.org Signed-off-by: Sasha Levin