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Date:   Sat, 2 May 2020 06:50:25 +0700
From:   Suravee Suthikulpanit <>
To:     Dave Hansen <>,,
        Sebastian Andrzej Siewior <>,
        Thomas Lendacky <>
Subject: Re: AMD / Memory Protection Keys


On 4/30/20 2:18 AM, Dave Hansen wrote:
> The docs for AMD's implementation of protection keys showed up[1].
> Welcome to the party!
> It all looks fine, except for this nugget:
> 	The MPK mechanism is ignored in the following cases:
> 	... for pages marked in the paging structures as read-only
> 	(R/W=0) or as supervisor addresses (U/S=0)
> That R/W=0 would mean that you can't access-disable read-only pages,
> which seems a bit goofy.  It's certainly a feature that I could imagine
> folks wanting to have.  Read-only pages might happen in unexpected
> places for things like mmap(PROT_WRITE)'d files or even CoW pages after
> fork().
> Is this an error in the docs?
> 1.;;sdata=LZLQjvlVT5xSnjyRt0alN0lHleh8VD7Sxx53RL1UrX0%3D&amp;reserved=0

Yes, we have checked with the hardware team and this is a mistake in the documentation.
The access disable bit (ADi) bit does apply to read-only pages. We will be correcting
the documentation. Thanks for pointing it out :)


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