linux-kernel - Re: [Xen-devel] [RFC 00/23] arm64: Add support for 64KB page granularity in Xen guest

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Message-ID: <55561605.4020805@oracle.com>
Date:	Fri, 15 May 2015 11:51:33 -0400
From:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:	David Vrabel <david.vrabel@...rix.com>,
	Julien Grall <julien.grall@...rix.com>,
	xen-devel@...ts.xenproject.org
CC:	wei.liu2@...rix.com, ian.campbell@...rix.com,
	stefano.stabellini@...citrix.com, tim@....org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	roger.pau@...rix.com
Subject: Re: [Xen-devel] [RFC 00/23] arm64: Add support for 64KB page granularity
 in Xen guest

On 05/15/2015 11:45 AM, David Vrabel wrote:
> On 14/05/15 18:00, Julien Grall wrote:
>> Hi all,
>>
>> ARM64 Linux is supporting both 4KB and 64KB page granularity. Although, Xen
>> hypercall interface and PV protocol are always based on 4KB page granularity.
>>
>> Any attempt to boot a Linux guest with 64KB pages enabled will result to a
>> guest crash.
>>
>> This series is a first attempt to allow those Linux running with the current
>> hypercall interface and PV protocol.
>>
>> This solution has been chosen because we want to run Linux 64KB in released
>> Xen ARM version or/and platform using an old version of Linux DOM0.
> The key problem I see with this approach is the confusion between guest
> page size and Xen page size.  This is going to be particularly
> problematic since the majority of development/usage will remain on x86
> where PAGE_SIZE == XEN_PAGE_SIZE.
>
> I think it would be nice to keep XEN_PAGE_SIZE etc out of front and
> backend drivers.  Perhaps with a suitable set of helper functions?

I am thinking exactly the same thing as I am going over these patches.

-boris
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