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Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition

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  Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition David Vrabel <david.vrabel@citrix.com> - 2015-07-24 11:30 +0200
    Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition David Vrabel <david.vrabel@citrix.com> - 2015-07-24 11:50 +0200
      Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition Julien Grall <julien.grall@citrix.com> - 2015-07-24 12:00 +0200
        Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition David Vrabel <david.vrabel@citrix.com> - 2015-07-24 12:40 +0200
          Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page  definition Ian Campbell <ian.campbell@citrix.com> - 2015-07-24 12:50 +0200
          Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition Julien Grall <julien.grall@citrix.com> - 2015-07-24 15:10 +0200
    Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition Julien Grall <julien.grall@citrix.com> - 2015-07-24 11:50 +0200

#1191630 — Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition

On 09/07/15 21:42, Julien Grall wrote:
> The Xen hypercall interface is always using 4K page granularity on ARM
> and x86 architecture.
> 
> With the incoming support of 64K page granularity for ARM64 guest, it
> won't be possible to re-use the Linux page definition in Xen drivers.
> 
> Introduce Xen page definition helpers based on the Linux page
> definition. They have exactly the same name but prefixed with
> XEN_/xen_ prefix.
> 
> Also modify page_to_pfn to use new Xen page definition.
>
> Signed-off-by: Julien Grall <julien.grall@citrix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
> Cc: David Vrabel <david.vrabel@citrix.com>
> ---
>     I'm wondering if we should drop page_to_pfn has the macro will likely
>     misuse when Linux is using 64KB page granularity.

I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
front/back drivers never deal with PFNs only GFNs.

David

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#1191635

On 24/07/15 10:39, Julien Grall wrote:
> Hi David,
> 
> On 24/07/15 10:28, David Vrabel wrote:
>> On 09/07/15 21:42, Julien Grall wrote:
>>> The Xen hypercall interface is always using 4K page granularity on ARM
>>> and x86 architecture.
>>>
>>> With the incoming support of 64K page granularity for ARM64 guest, it
>>> won't be possible to re-use the Linux page definition in Xen drivers.
>>>
>>> Introduce Xen page definition helpers based on the Linux page
>>> definition. They have exactly the same name but prefixed with
>>> XEN_/xen_ prefix.
>>>
>>> Also modify page_to_pfn to use new Xen page definition.
>>>
>>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>> Cc: David Vrabel <david.vrabel@citrix.com>
>>> ---
>>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>>     misuse when Linux is using 64KB page granularity.
>>
>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
>> front/back drivers never deal with PFNs only GFNs.
> 
> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
> series have them.

I suggesting that you introduce these.

David
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#1191655

On 24/07/15 10:48, David Vrabel wrote:
> On 24/07/15 10:39, Julien Grall wrote:
>> Hi David,
>>
>> On 24/07/15 10:28, David Vrabel wrote:
>>> On 09/07/15 21:42, Julien Grall wrote:
>>>> The Xen hypercall interface is always using 4K page granularity on ARM
>>>> and x86 architecture.
>>>>
>>>> With the incoming support of 64K page granularity for ARM64 guest, it
>>>> won't be possible to re-use the Linux page definition in Xen drivers.
>>>>
>>>> Introduce Xen page definition helpers based on the Linux page
>>>> definition. They have exactly the same name but prefixed with
>>>> XEN_/xen_ prefix.
>>>>
>>>> Also modify page_to_pfn to use new Xen page definition.
>>>>
>>>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>>> Cc: David Vrabel <david.vrabel@citrix.com>
>>>> ---
>>>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>>>     misuse when Linux is using 64KB page granularity.
>>>
>>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
>>> front/back drivers never deal with PFNs only GFNs.
>>
>> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
>> series have them.
> 
> I suggesting that you introduce these.

It's still not clear to me what you are suggesting here... Do you
suggest to rename xen_pfn_to_page and xen_page_to_pfn by xen_gfn_to_page
and xen_page_to_gfn?

Regards,

-- 
Julien Grall
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#1191701

On 24/07/15 10:51, Julien Grall wrote:
> On 24/07/15 10:48, David Vrabel wrote:
>> On 24/07/15 10:39, Julien Grall wrote:
>>> Hi David,
>>>
>>> On 24/07/15 10:28, David Vrabel wrote:
>>>> On 09/07/15 21:42, Julien Grall wrote:
>>>>> The Xen hypercall interface is always using 4K page granularity on ARM
>>>>> and x86 architecture.
>>>>>
>>>>> With the incoming support of 64K page granularity for ARM64 guest, it
>>>>> won't be possible to re-use the Linux page definition in Xen drivers.
>>>>>
>>>>> Introduce Xen page definition helpers based on the Linux page
>>>>> definition. They have exactly the same name but prefixed with
>>>>> XEN_/xen_ prefix.
>>>>>
>>>>> Also modify page_to_pfn to use new Xen page definition.
>>>>>
>>>>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>>>> Cc: David Vrabel <david.vrabel@citrix.com>
>>>>> ---
>>>>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>>>>     misuse when Linux is using 64KB page granularity.
>>>>
>>>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
>>>> front/back drivers never deal with PFNs only GFNs.
>>>
>>> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
>>> series have them.
>>
>> I suggesting that you introduce these.
> 
> It's still not clear to me what you are suggesting here... Do you
> suggest to rename xen_pfn_to_page and xen_page_to_pfn by xen_gfn_to_page
> and xen_page_to_gfn?

Effectively, yes but it would be better to think that:

PFNs index guest-sized pages (which may be 64 KiB).

GFNs index Xen-sized pages (which is always 4 KiB).

David
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#1191709 — Re: [Xen-devel] [PATCH v2 01/20] xen: Add Xen specific page definition

On Fri, 2015-07-24 at 11:34 +0100, David Vrabel wrote:
> it would be better to think that:
> 
> PFNs index guest-sized pages (which may be 64 KiB).
> 
> GFNs index Xen-sized pages (which is always 4 KiB).

This concept could be usefully added to the comment in
xen/include/xen/mm.h IMHO.


> 
> David
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#1191807

On 24/07/15 11:34, David Vrabel wrote:
> On 24/07/15 10:51, Julien Grall wrote:
>> On 24/07/15 10:48, David Vrabel wrote:
>>> On 24/07/15 10:39, Julien Grall wrote:
>>>> Hi David,
>>>>
>>>> On 24/07/15 10:28, David Vrabel wrote:
>>>>> On 09/07/15 21:42, Julien Grall wrote:
>>>>>> The Xen hypercall interface is always using 4K page granularity on ARM
>>>>>> and x86 architecture.
>>>>>>
>>>>>> With the incoming support of 64K page granularity for ARM64 guest, it
>>>>>> won't be possible to re-use the Linux page definition in Xen drivers.
>>>>>>
>>>>>> Introduce Xen page definition helpers based on the Linux page
>>>>>> definition. They have exactly the same name but prefixed with
>>>>>> XEN_/xen_ prefix.
>>>>>>
>>>>>> Also modify page_to_pfn to use new Xen page definition.
>>>>>>
>>>>>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>>>>>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>>>>>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>>>>>> Cc: David Vrabel <david.vrabel@citrix.com>
>>>>>> ---
>>>>>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>>>>>     misuse when Linux is using 64KB page granularity.
>>>>>
>>>>> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
>>>>> front/back drivers never deal with PFNs only GFNs.
>>>>
>>>> What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
>>>> series have them.
>>>
>>> I suggesting that you introduce these.
>>
>> It's still not clear to me what you are suggesting here... Do you
>> suggest to rename xen_pfn_to_page and xen_page_to_pfn by xen_gfn_to_page
>> and xen_page_to_gfn?
> 
> Effectively, yes but it would be better to think that:
> 
> PFNs index guest-sized pages (which may be 64 KiB).
> 
> GFNs index Xen-sized pages (which is always 4 KiB).

If I'm understanding correctly you mean:

#define xen_page_to_gfn(page)	\
((page_to_pfn(page) << PAGE_SHIFT) >> XEN_PAGE_SHIFT))

static page_to_mfn(struct page *page)
{
	return pfn_to_mfn(xen_page_to_gfn(page));
}

Although in some place you are suggesting to use:

xen_page_to_gfn(virt_to_page(info->intf)) (see patch #11) where it
suggests to rename page_to_mfn in xen_page_to_gfn.

I think it would make more sense to use the latter one. We would also
need to name to describe a PFN (pseudo-physical frame number based on
xen/include/xen/mm.h) but with 4K granularity and not the Linux granularity.

It's useful to have it in some place in order to iter on the 4K pfn (see
gnttab_foreach_grant and xen_apply_to_page). Maybe xpfn for Xen
pseudo-physical frame number?

I will preprend some patches into this serie to rename the function with
their correct naming.

I have in mind pfn_to_mfn which should be name into pfn_to_gfn given the
usage. Similarly, this function is mis-used on ARM because the function
may return an MFN where we expect a GFN.

Regards,

-- 
Julien Grall
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#1191647

Hi David,

On 24/07/15 10:28, David Vrabel wrote:
> On 09/07/15 21:42, Julien Grall wrote:
>> The Xen hypercall interface is always using 4K page granularity on ARM
>> and x86 architecture.
>>
>> With the incoming support of 64K page granularity for ARM64 guest, it
>> won't be possible to re-use the Linux page definition in Xen drivers.
>>
>> Introduce Xen page definition helpers based on the Linux page
>> definition. They have exactly the same name but prefixed with
>> XEN_/xen_ prefix.
>>
>> Also modify page_to_pfn to use new Xen page definition.
>>
>> Signed-off-by: Julien Grall <julien.grall@citrix.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
>> Cc: David Vrabel <david.vrabel@citrix.com>
>> ---
>>     I'm wondering if we should drop page_to_pfn has the macro will likely
>>     misuse when Linux is using 64KB page granularity.
> 
> I think we want xen_gfn_to_page() and xen_page_to_gfn() and Xen
> front/back drivers never deal with PFNs only GFNs.

What is xen_gfn_to_page and xen_page_to_gfn? Neither Linux, nor my
series have them.

Regards,

-- 
Julien Grall
--
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