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Date:   Wed, 24 Jan 2018 13:29:08 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Woodhouse <dwmw2@infradead.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        KarimAllah Ahmed <karahmed@amazon.de>,
        linux-kernel@vger.kernel.org, Andi Kleen <ak@linux.intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andy Lutomirski <luto@kernel.org>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Asit Mallick <asit.k.mallick@intel.com>,
        Borislav Petkov <bp@suse.de>,
        Dan Williams <dan.j.williams@intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "H . Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@amd.com>,
        Joerg Roedel <joro@8bytes.org>,
        Jun Nakajima <jun.nakajima@intel.com>,
        Laura Abbott <labbott@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Tom Lendacky <thomas.lendacky@amd.com>, kvm@vger.kernel.org,
        x86@kernel.org
Subject: Re: [RFC 05/10] x86/speculation: Add basic IBRS support
 infrastructure
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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?