linux-kernel - Re: [RFC PATCH 3/11] x86, mm, pat: Change reserve

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Date:	Tue, 15 Jul 2014 17:10:01 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	plagnioj@...osoft.com, tomi.valkeinen@...com,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stefan Bader <stefan.bader@...onical.com>,
	Dave Airlie <airlied@...il.com>, Borislav Petkov <bp@...en8.de>
Subject: Re: [RFC PATCH 3/11] x86, mm, pat: Change reserve_memtype() to
 handle WT type

On Tue, 2014-07-15 at 12:56 -0700, Andy Lutomirski wrote:
> On Tue, Jul 15, 2014 at 12:34 PM, Toshi Kani <toshi.kani@...com> wrote:
> > This patch changes reserve_memtype() to handle the new WT type.
> > When (!pat_enabled && new_type), it continues to set either WB
> > or UC- to *new_type.  When pat_enabled, it can reserve a given
> > non-RAM range for WT.  At this point, it may not reserve a RAM
> > range for WT since reserve_ram_pages_type() uses the page flags
> > limited to three memory types, WB, WC and UC.
> 
> FWIW, last time I looked at this, it seemed like all the fancy
> reserve_ram_pages stuff was unnecessary: shouldn't the RAM type be
> easy to track in the direct map page tables?

Are you referring the direct map page tables as the kernel page
directory tables (pgd/pud/..)?

I think it needs to be able to keep track of the memory type per a
physical memory range, not per a translation, in order to prevent
aliasing of the memory type.

Thanks,
-Toshi

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