For testing, development, and experimentation, add the ability to force the kernel to behave as if the CPU has a bug, even if it doesn't, using a command-line param. Also do this in general for CPU flags, since: - The infrastructure is the same so there is almost no extra implementation complexity. - While setting random CPU flags is certain to break the kernel in mysterious and horrifying ways, this is not dramatically worse than setting CPU bugs. Although CPU bug mitigations don't have any very obvious ways to break the system if run on the wrong hardware, it's still very much an unsupported configuration, even beyond the security concern implied breaking mitigation logic. Since a taint and scary docs are necessary regardless, supporting arbitrary CPU flags doesn't add significant maintenance/support burden either. Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx> --- Changes in v3: - Added pre-patch to cleanup some unnecessary macro usage. - More cleanups to commentary & commit messages. - Link to v2: https://lore.kernel.org/r/20241220-force-cpu-bug-v2-0-7dc71bce742a@xxxxxxxxxx Changes in v2: - Switched from a bugs-only force_cpu_bug= to a more general setcpuid=. - Made it taint the kernel. - Made docs sound scarier. - Spellchecked and avoided new usage of personal pronouns. - Link to v1: https://lore.kernel.org/r/20241119-force-cpu-bug-v1-1-2aa31c6c1ccf@xxxxxxxxxx --- Brendan Jackman (4): x86/cpu: Remove some macros about feature names x86/cpu: Create helper to parse clearcpuid param x86/cpu: Add setcpuid cmdline param x86/cpu: Enable modifying bug flags with {clear,set}cpuid arch/x86/include/asm/cpufeature.h | 6 +- arch/x86/kernel/cpu/common.c | 147 +++++++++++++++++++++++--------------- 2 files changed, 91 insertions(+), 62 deletions(-) --- base-commit: 83f8eec51fc484fe20f8d20171f6d450080c04ea change-id: 20241119-force-cpu-bug-94a08ab0239f Best regards, -- Brendan Jackman <jackmanb@xxxxxxxxxx>
