linux-kernel - Re: [Xen-devel] [PATCH V2 3/3] xen: eliminate scalability issues from initial mapping setup

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Message-ID: <54199DE7.6010306@citrix.com>
Date:	Wed, 17 Sep 2014 15:42:47 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Juergen Gross <jgross@...e.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <konrad.wilk@...cle.com>,
	<boris.ostrovsky@...cle.com>, <jbeulich@...e.com>
Subject: Re: [Xen-devel] [PATCH V2 3/3] xen: eliminate scalability issues
 from initial mapping setup

On 17/09/14 15:20, Juergen Gross wrote:
> On 09/17/2014 04:07 PM, David Vrabel wrote:
>> 
>>
>> Are you missing a ClearPagePinned(..) here?
> 
> Probably, yes.

Jan pointed out that this is not needed.

>>> @@ -1529,6 +1604,22 @@ static pte_t __init mask_rw_pte(pte_t *ptep,
>>> pte_t pte)
>>>   #else /* CONFIG_X86_64 */
>>>   static pte_t __init mask_rw_pte(pte_t *ptep, pte_t pte)
>>>   {
>>> +    unsigned long pfn;
>>> +
>>> +    if (xen_feature(XENFEAT_writable_page_tables) ||
>>> +        xen_feature(XENFEAT_auto_translated_physmap) ||
>>> +        xen_start_info->mfn_list >= __START_KERNEL_map)
>>> +        return pte;
>>> +
>>> +    /*
>>> +     * Pages belonging to the initial p2m list mapped outside the
>>> default
>>> +     * address range must be mapped read-only.
>>
>> Why?  I didn't think was anything special about these MFNs.
> 
> The hypervisor complained when I did otherwise. I think the main reason
> is that the hypervisor will set up some more page tables to be able to
> map then mfn_list outside the "normal" address range. They are located
> in the range starting at xen_start_info->first_p2m_pfn (otherwise the
> info in first_p2m_pfn and nr_p2m_frames wouldn't be needed).

Ok. Can you expand the comment to say this?

David
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