linux-kernel - Re: [PATCH 4.9 43/92] x86/pti: Do not enable PTI on CPUs which are not vulnerable to Meltdown

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Date:   Tue, 13 Feb 2018 16:00:07 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Nick Lowe <nick.lowe@...il.com>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        David Woodhouse <dwmw@...zon.co.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...e.de>,
        Dave Hansen <dave.hansen@...el.com>,
        gnomes@...rguk.ukuu.org.uk, ak@...ux.intel.com,
        ashok.raj@...el.com, karahmed@...zon.de, arjan@...ux.intel.com,
        torvalds@...ux-foundation.org, peterz@...radead.org,
        Borislav Petkov <bp@...en8.de>, pbonzini@...hat.com,
        tim.c.chen@...ux.intel.com
Subject: Re: [PATCH 4.9 43/92] x86/pti: Do not enable PTI on CPUs which are
 not vulnerable to Meltdown

On Tue, Feb 13, 2018 at 01:34:07PM +0000, Nick Lowe wrote:
> Hi,
> 
> This does not seem to have subsumed the AMD specific code in
> 
> x86/pti: Do not enable PTI on CPUs which are not vulnerable to Meltdown
> Commit a8799fd14d9f7f385a5a5c86cde247caf4bb0320
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/?h=v4.9.81&id=a8799fd14d9f7f385a5a5c86cde247caf4bb0320
> 
> x86/kaiser: Check boottime cmdline params
> Commit 8018307a45a90ab2eecfd03d48b7efb31707df37
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/commit/arch/x86/mm/kaiser.c?h=v4.9.75&id=8018307a45a90ab2eecfd03d48b7efb31707df37
> 
> Here, we can see:
> 
> +skip:
> + if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD)
> + goto disable;
> 
> Refer to 4.9.81's kaiser.c
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/arch/x86/mm/kaiser.c?h=v4.9.81
> 
> Also 4.4.115's kaiser.c
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git/tree/arch/x86/mm/kaiser.c?h=v4.4.115

So, any hints on what you think should be the correct fix here?

thanks,

greg k-h