From mboxrd@z Thu Jan  1 00:00:00 1970
From: steve.capper@arm.com (Steve Capper)
Date: Fri, 7 Sep 2018 14:59:08 +0100
Subject: [PATCH 0/5] 52-bit userspace VAs
In-Reply-To: <53f6d3aa-ffd9-8452-4ad6-847132b975a9@redhat.com>
References: <20180829124543.25314-1-steve.capper@arm.com>
 <53f6d3aa-ffd9-8452-4ad6-847132b975a9@redhat.com>
Message-ID: <20180907135907.snnns2aym3jhu2cc@capper-debian.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Sep 07, 2018 at 02:22:49AM -0400, Jon Masters wrote:
> On 08/29/2018 08:45 AM, Steve Capper wrote:
> > This patch series brings support for 52-bit userspace VAs to systems that
> > have ARMv8.2-LVA and are running with a 48-bit VA_BITS and a 64KB
> > PAGE_SIZE.
> > 
> > If no hardware support is present, the kernel runs with a 48-bit VA space
> > for userspace.
> > 
> > Userspace can exploit this feature by providing an address hint to mmap
> > where addr[51:48] != 0. Otherwise all the VA mappings will behave in the
> > same way as a 48-bit VA system (this is to maintain compatibility with
> > software that assumes the maximum VA size on arm64 is 48-bit).
> > 
> > This patch series applies to 4.19-rc1.
> > 
> > Testing was in a model with Trusted Firmware and UEFI for boot.
> 
> This is great stuff. I'm hoping to catch up at Connect and discuss.
> 
> Help me understand something. Without the kernel side of this patch, and
> the increase in linear map for installed RAM, what upside do I see other
> than being able to allocate from a higher VA space?
>

Hi Jon,
The main benefit from this series is that it allows for 52-bit VA
testing to take place in userspace on smaller systems.

Cheers,
-- 
Steve