linux-kernel - Re: [RFC 05/10] x86/speculation: Add basic IBRS support infrastructure

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Date:   Wed, 24 Jan 2018 13:29:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
        x86@...nel.org
Subject: Re: [RFC 05/10] x86/speculation: Add basic IBRS support
 infrastructure

On Wed, Jan 24, 2018 at 12:14:51PM +0000, David Woodhouse wrote:
> On Wed, 2018-01-24 at 09:47 +0100, Peter Zijlstra wrote:
> > 
> > Typically tglx likes to use x86_match_cpu() for these things; see also
> > commit: bd9240a18edfb ("x86/apic: Add TSC_DEADLINE quirk due to
> > errata").
> 
> Ewww.
> 
> static u32 hsx_deadline_rev(void)
> {
>        switch (boot_cpu_data.x86_mask) {
>        case 0x02: return 0x3a; /* EP */
>        case 0x04: return 0x0f; /* EX */
>        }
> 
>        return ~0U;
> }
> ...
> static const struct x86_cpu_id deadline_match[] = {
>        DEADLINE_MODEL_MATCH_FUNC( INTEL_FAM6_HASWELL_X,        hsx_deadline_rev),
>        DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_BROADWELL_X,      0x0b000020),
>        DEADLINE_MODEL_MATCH_FUNC( INTEL_FAM6_BROADWELL_XEON_D, bdx_deadline_rev),
>        DEADLINE_MODEL_MATCH_REV ( INTEL_FAM6_SKYLAKE_X,        0x02000014),
> ...
> 
>        /*
>         * Function pointers will have the MSB set due to address layout,
>         * immediate revisions will not.
>         */
>        if ((long)m->driver_data < 0)
>                rev = ((u32 (*)(void))(m->driver_data))();
>        else
>                rev = (u32)m->driver_data;
> 
> EWWWW!
> 

Yes :/

We could look at extending x86_cpu_id and x86_match_cpu with a stepping
option I suppose, but that might be lots of churn.

Thomas?