linux-kernel - Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre

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Date:   Wed, 2 May 2018 14:20:52 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jörg Otte <jrg.otte@...il.com>
cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [v4.17-rcx] Lost IBPB, IBRS_FW support for spectre_v2
 mitigation.

On Wed, 2 May 2018, Jörg Otte wrote:
> 2018-05-02 11:02 GMT+02:00 Thomas Gleixner <tglx@...utronix.de>:
> > 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