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

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Date:	Wed, 17 Sep 2014 16:47:41 +0200
From:	Juergen Gross <jgross@...e.com>
To:	David Vrabel <david.vrabel@...rix.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 09/17/2014 04:42 PM, David Vrabel wrote:
> 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?

Already did. :-)


Juergen
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