linux-kernel - Re: Overlapping ioremap() calls, set_memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALCETrUQsf7S-b+zDrof0g61NnSB3XuqdAxjsHyJfjT3D39D3Q@mail.gmail.com>
Date:	Thu, 10 Mar 2016 22:47:55 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Toshi Kani <toshi.kani@....com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	Toshi Kani <toshi.kani@...com>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Dave Airlie <airlied@...hat.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>, X86 ML <x86@...nel.org>,
	Daniel Vetter <daniel.vetter@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Brian Gerst <brgerst@...il.com>
Subject: Re: Overlapping ioremap() calls, set_memory_*() semantics

On Mon, Mar 7, 2016 at 9:03 AM, Toshi Kani <toshi.kani@....com> wrote:
> Let me try to summarize...
>
> The original issue Luis brought up was that drivers written to work with
> MTRR may create a single ioremap range covering multiple cache attributes
> since MTRR can overwrite cache attribute of a certain range.  Converting
> such drivers with PAT-based ioremap interfaces, i.e. ioremap_wc() and
> ioremap_nocache(), requires a separate ioremap map for each cache
> attribute, which can be challenging as it may result in overlapping ioremap
> ranges (in his term) with different cache attributes.
>
> So, Luis asked about 'sematics of overlapping ioremap()' calls.  Hence, I
> responded that aliasing mapping itself is supported, but alias with
> different cache attribute is not.  We have checks in place to detect such
> condition.  Overlapping ioremap calls with a different cache attribute
> either fails or gets redirected to the existing cache attribute on x86.

A little off-topic, but someone reminded me recently: most recent CPUs
have self-snoop.  It's poorly documented, but on self-snooping CPUs, I
think that a lot of the aliasing issues go away.  We may be able to
optimize the code quite a bit on these CPUs.

I also wonder whether we can drop a bunch of the memtype tracking.
After all, if we have aliases of different types on a self-snooping
CPU and /dev/mem is locked down hard enough, we could maybe get away
with letting self-snoop handle all the conflicts.

(We could also make /dev/mem always do UC if it would help.)

--Andy