• David Woodhouse's avatar
    x86/cpuid: Fix up "virtual" IBRS/IBPB/STIBP feature bits on Intel · 7fcae111
    David Woodhouse authored
    Despite the fact that all the other code there seems to be doing it, just
    using set_cpu_cap() in early_intel_init() doesn't actually work.
    
    For CPUs with PKU support, setup_pku() calls get_cpu_cap() after
    c->c_init() has set those feature bits. That resets those bits back to what
    was queried from the hardware.
    
    Turning the bits off for bad microcode is easy to fix. That can just use
    setup_clear_cpu_cap() to force them off for all CPUs.
    
    I was less keen on forcing the feature bits *on* that way, just in case
    of inconsistencies. I appreciate that the kernel is going to get this
    utterly wrong if CPU features are not consistent, because it has already
    applied alternatives by the time secondary CPUs are brought up.
    
    But at least if setup_force_cpu_cap() isn't being used, we might have a
    chance of *detecting* the lack of the corresponding bit and either
    panicking or refusing to bring the offending CPU online.
    
    So ensure that the appropriate feature bits are set within get_cpu_cap()
    regardless of how many extra times it's called.
    
    Fixes: 2961298e ("x86/cpufeatures: Clean up Spectre v2 related CPUID flags")
    Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Cc: karahmed@amazon.de
    Cc: peterz@infradead.org
    Cc: bp@alien8.de
    Link: https://lkml.kernel.org/r/1517322623-15261-1-git-send-email-dwmw@amazon.co.uk
    7fcae111
intel.c 27 KB