Re: [for-4.10] Re: [PATCH v2] tools/libxl: mark special pages as reserved in e820 map for PVH

From: Juergen Gross <jgross@suse.com>
To: "Julien Grall" <julien.grall@linaro.org>,
	"Roger Pau Monné" <roger.pau@citrix.com>
Cc: xen-devel@lists.xenproject.org, julien.grall@arm.com,
	wei.liu2@citrix.com, ian.jackson@eu.citrix.com
Subject: Re: [for-4.10] Re: [PATCH v2] tools/libxl: mark special pages as reserved in e820 map for PVH
Date: Wed, 6 Dec 2017 12:57:06 +0100	[thread overview]
Message-ID: <d24f61b3-b058-742f-cd6c-c0bce1dd3678@suse.com> (raw)
In-Reply-To: <4db6f077-9850-c9ac-0b87-f02407879ea3@linaro.org>

On 06/12/17 12:50, Julien Grall wrote:
> Hi,
> 
> On 12/06/2017 11:47 AM, Roger Pau Monné wrote:
>> On Wed, Dec 06, 2017 at 12:22:00PM +0100, Juergen Gross wrote:
>>> On 06/12/17 10:53, Julien Grall wrote:
>>>> Hi Juergen,
>>>>
>>>> On 12/05/2017 04:19 PM, Juergen Gross wrote:
>>>>> On 05/12/17 16:23, Julien Grall wrote:
>>>>>> Hi Juergen,
>>>>>>
>>>>>> On 04/12/17 15:49, Juergen Gross wrote:
>>>>>>> On 21/11/17 12:06, Juergen Gross wrote:
>>>>>>>> The "special pages" for PVH guests include the frames for
>>>>>>>> console and
>>>>>>>> Xenstore ring buffers. Those have to be marked as "Reserved" in the
>>>>>>>> guest's E820 map, as otherwise conflicts might arise later e.g.
>>>>>>>> when
>>>>>>>> hotplugging memory into the guest.
>>>>>>>>
>>>>>>>> Signed-off-by: Juergen Gross <jgross@suse.com>
>>>>>>>> ---
>>>>>>>> This is a bugfix for PVH guests. Please consider for 4.10.
>>>>>>>
>>>>>>> Ping?
>>>>>>
>>>>>> I was waiting an ack from tools maintainers before looking for a
>>>>>> release
>>>>>> perspective.
>>>>>>
>>>>>> I would recommend to tag your patch is 4.10 to help reviewers
>>>>>> prioritize
>>>>>> review on your patch. I have done it now.
>>>>>>
>>>>>> I am looking at releasing Xen 4.10 in the next few days. Can you
>>>>>> explain
>>>>>> the pros/cons of this patch?
>>>>>
>>>>> Pros: PVH guests with 4GB of memory or more will work. :-)
>>>>
>>>> They never worked before? Or is it a regression? If it is a regression
>>>> when did it appear?
>>>
>>> Hmm, seems we are lucky: Linux kernel will not try to map any memory
>>> there (I just tested it). So we don't need that patch in 4.10 for Linux
>>> running as PVH guest. Not sure about BSD, though.
>>
>> I haven't yet committed any PVHv2 support to FreeBSD, but in any case
>> I always avoid using memory below 4GB just in case...
> 
> I will defer this patch post 4.10. We can add a release note if you
> think it is worth it.

I don't think that is needed.

And in case someone hits this problem we can easily apply the patch to
a 4.10 update release later.

Juergen

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