Subject: Re: [PATCH v2] Call xen_cleanhighmap() with 4MB aligned for page
 tables mapping
To: Juergen Gross <jgross@suse.com>,
        Zhenzhong Duan <zhenzhong.duan@oracle.com>, mingo@redhat.com,
        tglx@linutronix.de, hpa@zytor.com
References: <85bd42d5-b0d2-40f5-81a9-14cb51ec4503@default>
 <d5d1fd24-ce7d-1e12-6522-e3cb220858a5@suse.com>
 <44ebc914-d1a3-06ac-9ec5-b866d5f04e0a@oracle.com>
 <9faf8d7b-227f-2ecd-26e6-44ae4270d469@suse.com>
Cc: x86@kernel.org, xen-devel@lists.xenproject.org,
        srinivas.eeda@oracle.com, joe.jin@oracle.com,
        linux-kernel@vger.kernel.org
From: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <df140683-63dd-02fa-f248-2fcb6d635d54@oracle.com>
Date: Wed, 27 Sep 2017 10:48:01 -0400
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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