Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre_v2 mitigation.
From: Thomas Gleixner
Date: Wed May 02 2018 - 08:21:05 EST
On Wed, 2 May 2018, JÃrg Otte wrote:
> 2018-05-02 11:02 GMT+02:00 Thomas Gleixner <tglx@xxxxxxxxxxxxx>:
> > Ok, I think I know what's going wrong in that steaming pile of horrors of
> > CPUID detection. I need to analyze it down to the roots, but if you have
> > cycles, can you please test the patch below?
> >
> > It's a hack and even if it fixes the problem I'm going to do it differently.
> >
> > Thanks,
> >
> > tglx
> >
> > 8<-------------------
> > --- a/arch/x86/kernel/cpu/common.c
> > +++ b/arch/x86/kernel/cpu/common.c
> > @@ -848,6 +848,11 @@ void get_cpu_cap(struct cpuinfo_x86 *c)
> > c->x86_power = edx;
> > }
> >
> > + if (c->extended_cpuid_level >= 0x80000008) {
> > + cpuid(0x80000008, &eax, &ebx, &ecx, &edx);
> > + c->x86_capability[CPUID_8000_0008_EBX] = ebx;
> > + }
> > +
> > if (c->extended_cpuid_level >= 0x8000000a)
> > c->x86_capability[CPUID_8000_000A_EDX] = cpuid_edx(0x8000000a);
> >
> > @@ -871,7 +876,6 @@ static void get_cpu_address_sizes(struct
> >
> > c->x86_virt_bits = (eax >> 8) & 0xff;
> > c->x86_phys_bits = eax & 0xff;
> > - c->x86_capability[CPUID_8000_0008_EBX] = ebx;
> > }
> > #ifdef CONFIG_X86_32
> > else if (cpu_has(c, X86_FEATURE_PAE) || cpu_has(c, X86_FEATURE_PSE36))
> >
>
> OK, that patch works for me!
Thanks for confirming. Still need to find a way which is less fragile, but
that's probably too much of churn for rc4....
At least I know exactly what's happening, so I can write a better changelog.
Thanks for testing!
tglx