linux-kernel - Re: [PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux

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Message-ID: <560BCB67.1060100@citrix.com>
Date:	Wed, 30 Sep 2015 12:45:43 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"wei.liu2@...rix.com" <wei.liu2@...rix.com>,
	"Ian.Campbell@...rix.com" <Ian.Campbell@...rix.com>,
	"stefano.stabellini@...citrix.com" <stefano.stabellini@...citrix.com>,
	"konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"david.vrabel@...rix.com" <david.vrabel@...rix.com>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"roger.pau@...rix.com" <roger.pau@...rix.com>,
	Suzuki Poulose <Suzuki.Poulose@....com>
Subject: Re: [PATCH v5 00/22] xen/arm64: Add support for 64KB page in Linux

On 30/09/15 12:32, Mark Rutland wrote:
> On Wed, Sep 30, 2015 at 11:45:15AM +0100, Julien Grall wrote:
>> Hi all,
> 
> Hi,
> 
>> 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.
> 
> Just to check, would this be expected to work with a 16K DomU (e.g.
> [2])?
> 
> From a quick scan it looks like the relaxations provided by this series
> should work so long as PAGE_SIZE % XEN_PAGE_SIZE == 0, assuming I
> haven't missed something.

Correct, this series is able to cope with any PAGE_SIZE as long as it's
a multiple of the granularity used by Xen (i.e 4KB on ARM).

>> There is room for improvement, such as support of 64KB grant, modification
>> of PV protocol to support different page size... They will be explored in a
>> separate patch series later.
>>
>> TODO list:
>>     - Convert xenfb to 64KB
>>     - Support for multiple page ring support
>>     - Support for 64KB in gnttdev
>>     - Support of non-indirect grant with 64KB frontend (patch sent [1])
>>     - It may be possible to move some common define between
>>     netback/netfront and blkfront/blkback in an header
> 
> Would any of these require more work to also handle 16K?

No. It should just boot on Xen as long as the CPU is support 16K
granularity.

Regards,

-- 
Julien Grall
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