linux-kernel - Re: [PATCH 0/29] arm meltdown fix backporting review for lts 4.9

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Date:   Tue, 13 Mar 2018 11:04:42 +0100
From:   Greg KH <greg@...ah.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Alex Shi <alex.shi@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        stable@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/29] arm meltdown fix backporting review for lts 4.9

On Wed, Mar 07, 2018 at 06:24:09PM +0000, Ard Biesheuvel wrote:
> On 2 March 2018 at 16:54, Greg KH <greg@...ah.com> wrote:
> > On Fri, Mar 02, 2018 at 05:14:50PM +0800, Alex Shi wrote:
> >>
> >>
> >> On 03/01/2018 11:24 PM, Greg KH wrote:
> >> > On Wed, Feb 28, 2018 at 11:56:22AM +0800, Alex Shi wrote:
> >> >> Hi All,
> >> >>
> >> >> This backport patchset fixed the meltdown issue, it's original branch:
> >> >> https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/log/?h=kpti
> >> >> A few dependency or fixingpatches are also picked up, if they are necessary
> >> >>  and no functional changes.
> >> >>
> >> >> The patchset also on repository:
> >> >>    git://git.linaro.org/kernel/linux-linaro-stable.git lts-4.9-spectrevv2
> >> >>
> >> >> No bug found yet from kernelci.org and lkft testing.
> >> >
> >> > No bugs is good, but does it actually fix the meltdown problem?  What
> >> > did you test it on?
> >>
> >> Oh, I have no A73/A75 cpu, so I can not reproduce meltdown bug.
> >
> > Then why should I trust this backport at all?
> >
> > Please test on the hardware that is affected, otherwise you do not know
> > if your patches do anything or not.
> >
> 
> I don't think it is feasible to test these backports by confirming
> that they make the fundamental issue go away. We simply don't have the
> code to reproduce all the variants, and we have to rely on the
> information provided by ARM Ltd. regarding which cores are affected
> and which aren't.

You really don't have the reproducers?  Please work with ARM to resolve
that, this should not be a non-tested set of patches.  That's really
worse than no patches at all, as if they were applied, that would
provide a false-sense of "all is fixed".

thanks,

greg k-h