From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
To: Dave Hansen <dave.hansen@intel.com>,
linux-kernel@vger.kernel.org, x86@kernel.org
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
hpa@zytor.com, jon.grimm@amd.com,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Thomas Lendacky <Thomas.Lendacky@amd.com>
Subject: Re: AMD / Memory Protection Keys
Date: Sat, 2 May 2020 06:50:25 +0700 [thread overview]
Message-ID: <01f3cf52-bb1e-f6a0-5810-c5e62ce5f302@amd.com> (raw)
In-Reply-To: <178377ad-efd6-d473-e10d-2928c171437e@intel.com>
Dave,
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. https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.amd.com%2Fsystem%2Ffiles%2FTechDocs%2F24593.pdf&data=02%7C01%7Csuravee.suthikulpanit%40amd.com%7C9ea21438bce6488589a308d7ec720d0d%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637237847630823928&sdata=LZLQjvlVT5xSnjyRt0alN0lHleh8VD7Sxx53RL1UrX0%3D&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 :)
Suravee
prev parent reply other threads:[~2020-05-01 23:50 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 9:01 [PATCH] x86/fpu: Warn only when CPU-provided sizes less than struct declaration Suravee Suthikulpanit
2019-12-03 10:34 ` Sebastian Andrzej Siewior
2019-12-06 8:14 ` Suravee Suthikulpanit
2019-12-03 17:27 ` Dave Hansen
2019-12-06 8:14 ` Suravee Suthikulpanit
2019-12-06 15:28 ` Dave Hansen
2019-12-11 5:24 ` Suravee Suthikulpanit
2019-12-11 14:13 ` Dave Hansen
2019-12-12 6:52 ` Suravee Suthikulpanit
2020-01-13 9:54 ` Suravee Suthikulpanit
2020-01-15 16:54 ` Dave Hansen
2020-04-29 19:18 ` AMD / Memory Protection Keys Dave Hansen
2020-05-01 23:50 ` Suravee Suthikulpanit [this message]
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