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Date: Wed, 22 Jun 2016 23:24:14 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: JITs and 52-bit VA
Message-ID: <20160622202414.GA20027@node.shutemov.name>
References: <4A8E6E6D-6CF7-4964-A62E-467AE287D415@linaro.org>
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To: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>, Andy Lutomirski <luto@amacapital.net>, Christopher Covington <cov@codeaurora.org>, Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>, Linaro Dev Mailman List <linaro-dev@lists.linaro.org>, Arnd Bergmann <arnd.bergmann@linaro.org>, Mark Brown <broonie@linaro.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Dmitry Safonov <dsafonov@virtuozzo.com>

On Wed, Jun 22, 2016 at 11:17:54PM +0300, Cyrill Gorcunov wrote:
> On Wed, Jun 22, 2016 at 12:56:56PM -0700, Dave Hansen wrote:
> > 
> > Yeah, cgroups don't make a lot of sense.
> > 
> > On x86, the 48-bit virtual address is even hard-coded in the ABI[1].  So
> > we can't change *any* program's layout without either breaking the ABI
> > or having it opt in.
> > 
> > But, we're also lucky to only have one VA layout since day one.
> > 
> > 1. www.x86-64.org/documentation/abi.pdf - a??... Therefore, conforming
> > processes may only use addresses from 0x00000000 00000000 to 0x00007fff
> > ffffffff .a??
> 
> Yes, but noone forces you to write conforming programs ;)
> After all while hw allows you to run VA with bits > than
> 48 it's fine, all side effects of breaking abi is up to
> program author (iirc on x86 there is up to 52 bits on
> hw level allowed, don't have specs under my hands?)

Nope. 48-bit VA (47-bit to userspace) and 46-bit PA.

-- 
 Kirill A. Shutemov

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