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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Message-ID: <CADSoG1sv4-YmRh8AwD7A93_eDLn4ZTwD0Y7C9jyRyh6nOvwqjQ@mail.gmail.com>
Date:   Tue, 13 Feb 2018 15:27:47 +0000
From:   Nick Lowe <nick.lowe@...il.com>
To:     Arjan van de Ven <arjan@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        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

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.

Regards,

Nick