Messages in this thread | | | Date | Tue, 6 Dec 2016 09:57:26 +0100 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH 3/6] x86/cpu: Re-apply forced caps every time cpu caps are re-read |
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On Mon, Dec 05, 2016 at 05:01:12PM -0800, Andy Lutomirski wrote: > Calling get_cpu_cap() will reset a bunch of CPU features. This will > cause the system to lose track of force-set and force-cleared > featueres in the words that are reset until the end of CPU > initialization. This can cause X86_FEATURE_FPU, for example, to > change back and forth during boot and potentially confuse CPU setup. > > To minimize the chance of confusion, re-apply forced caps every time > get_cpu_cap() is called. > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > --- > arch/x86/kernel/cpu/common.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 347ae0a19380..24e1e4004d42 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -758,6 +758,13 @@ void get_cpu_cap(struct cpuinfo_x86 *c) > c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a); > > init_scattered_cpuid_features(c); > + > + /* > + * Clear/Set all flags overridden by options, after probe. > + * This needs to happen each time we re-probe, which may happen > + * several times during CPU initialization. > + */ > + apply_forced_caps(c);
I guess...
Although I have to say all that early capabilities detection has grown a lot of cruft during the years and is nuts. And calling get_cpu_cap() multiple times is simply plain wrong.
What we should do is read CPUID *once*, filter out caps and set our internal representation bits and be done with it.
Stuff like setup_pku() which *sets* CPUID bits will then have to run *before* we do the detection and that's it.
But I guess that's future work.
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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