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 17:32:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Nick Lowe <nick.lowe@...il.com>
Cc:     Arjan van de Ven <arjan@...ux.intel.com>,
        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,
        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 03:27:47PM +0000, Nick Lowe wrote:
> Hi Arjan and Greg,
> 
> Sorry if I am not being clear enough.
> 
> My point is that there is a check for X86_VENDOR_AMD now in two places.
> 
> It is still hardcoded for the auto boot option which I think should
> not be there. The patch on that basis looked incomplete to me.
> 
> Put another way, there is no effect to the auto option where the
> contents of cpu_no_meltdown[] are changed and
> cpu_vulnerable_to_meltdown returns differently.
> 
> The auto option does not make use of a determination of the
> X86_BUG_CPU_MELTDOWN state.
> 
> This seems wrong to me. It does not seem correct to me for the auto
> option to have this duplication with a check for just X86_VENDOR_AMD.

Do you have a patch that reflects what you want to see changed here?

And can you test it?  :)

I don't have any AMD hardware, sorry.

thanks,

greg k-h