linux-kernel - RE: [PATCH v4] arm64: Add workaround for Fujitsu A64FX erratum 010001

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Message-ID: <8898674D84E3B24BA3A2D289B872026A6A313313@G01JPEXMBKW03>
Date:   Fri, 15 Feb 2019 12:36:23 +0000
From:   "Zhang, Lei" <zhang.lei@...fujitsu.com>
To:     'James Morse' <james.morse@....com>,
        Mark Rutland <mark.rutland@....com>
CC:     'Will Deacon' <will.deacon@....com>,
        'Catalin Marinas' <catalin.marinas@....com>,
        "'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
        "'linux-arm-kernel@...ts.infradead.org'" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH v4] arm64: Add workaround for Fujitsu A64FX erratum
 010001

Hi guys,


> -----Original Message-----
> From: James Morse [mailto:james.morse@....com]
> Sent: Friday, February 15, 2019 3:23 AM
> To: Mark Rutland; Zhang, Lei 
> Cc: 'Will Deacon'; 'Catalin Marinas'; 'linux-kernel@...r.kernel.org';
> 'linux-arm-kernel@...ts.infradead.org'
> Subject: Re: [PATCH v4] arm64: Add workaround for Fujitsu A64FX erratum 010001

> I think we should do this: never set NFDx on A64FX. I don't think we can maintain
> the TCR
> swivel before any memory access in the KPTI trampoline. (It already uses the
> FAR as a
> scratch register!)
> 
> The errata means we can't use these bits. Its simpler than trying to work around
> the symptoms.

I think you mean it may be a problem to modify the KPTI trampoline 
because some patches about KPTI will be merged to mainline in the near future.
I understood that.
I should discuss with my colleagues whether we can set NFDx=0 all of time on A64FX.

And thanks for your patch.
If we can set NFDx=0 all of time, I will review, test and report the result.

Best Regards,
Zhang Lei