linux-kernel - Re: [PATCH v2] Call xen_cleanhighmap() with 4MB aligned for page tables mapping

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Date:   Wed, 27 Sep 2017 10:48:01 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>,
        Zhenzhong Duan <zhenzhong.duan@...cle.com>, mingo@...hat.com,
        tglx@...utronix.de, hpa@...or.com
Cc:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        srinivas.eeda@...cle.com, joe.jin@...cle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Call xen_cleanhighmap() with 4MB aligned for page
 tables mapping

On 09/27/2017 10:33 AM, Juergen Gross wrote:
> On 27/09/17 15:38, Boris Ostrovsky wrote:
>> On 09/27/2017 05:43 AM, Juergen Gross wrote:
>>> On 27/09/17 11:41, Zhenzhong Duan wrote:
>>>> When bootup a PVM guest with large memory(Ex.240GB), XEN provided initial
>>>> mapping overlaps with kernel module virtual space. When mapping in this space
>>>> is cleared by xen_cleanhighmap(), in certain case there could be an 2MB mapping
>>>> left. This is due to XEN initialize 4MB aligned mapping but xen_cleanhighmap()
>>>> finish at 2MB boundary.
>> Does this mapping need to be 4MB-aligned?
> I guess you are questioning the alignment of addr to be 4MB?
> In this case you are right: the end of the mapping is 4MB aligned, as
> correctly stated in the comment added.

Yes, and my question is why does it need to be aligned on 4MB. Doesn't
2MB alignment suffice?

-boris