Messages in this thread | | | Date | Sun, 20 Sep 2020 10:36:26 +0200 | From | Borislav Petkov <> | Subject | Re: [PATCH] x86/boot: Delay BSP init until after FPU initialization |
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On Sun, Sep 20, 2020 at 10:03:10AM +0900, Mike Hommey wrote: > FPU initialization handles the clearcpuid command line argument. If it > comes after BSP init, clearcpuid cannot be used to disable features that > trigger some parts of the BSP init code. > > Signed-off-by: Mike Hommey <mh@glandium.org> > --- > arch/x86/kernel/cpu/common.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > I was trying to use clearcpuid=440 to disable X86_FEATURES_AMD_SSBD to > reproduce the behavior that happens on Zen/Zen+ on a Zen2 machine, but > that didn't work because the command line is handled after the setup for > X86_FEATURE_LS_CFG_SSBD. > > I tought about either moving the command line handling earlier, but it > seems there wasn't a specific reason for BSP init being earlier than FPU > initialization so I went with reordering those instead.
Our boot order is fragile and the functionality in fpu__init_parse_early_param() which does the clearcpuid= parsing should be independent from FPU, as your use case shows.
So I'd prefer if you moved that function perhaps to right after the call
setup_force_cpu_cap(X86_FEATURE_CPUID);
in early_identify_cpu() and renamed it to something generic instead.
Thx.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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