recreate monitor page table?

recreate monitor page table?

[Li, Xin B]

What's the intent to recreate monitor page table when shadow levels
changes in sh_update_paging_modes?
-Xin

Re: recreate monitor page table?

[Tim Deegan]

At 10:13 +0800 on 18 Apr (1176891228), Li, Xin B wrote:
> What's the intent to recreate monitor page table when shadow levels
> changes in sh_update_paging_modes?

The monitor tables have to have a different layout in different shadow
paging modes so that linear maps of the shadows can work properly.

Cheers,

Tim.

-- 
Tim Deegan <Tim.Deegan@xensource.com>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

RE: recreate monitor page table?

[Li, Xin B]

>At 10:13 +0800 on 18 Apr (1176891228), Li, Xin B wrote:
>> What's the intent to recreate monitor page table when shadow levels
>> changes in sh_update_paging_modes?
>
>The monitor tables have to have a different layout in different shadow
>paging modes so that linear maps of the shadows can work properly.
>

On x86_64, monitor page table should always be 4 level, and we can
uninstall the old shadow linear entry and install new shadow paging mode
entry, why even recreate the monitor top level page?
-Xin

Re: RE: recreate monitor page table?

[Keir Fraser]

On 18/4/07 16:46, "Li, Xin B" <xin.b.li@intel.com> wrote:

>> At 10:13 +0800 on 18 Apr (1176891228), Li, Xin B wrote:
>>> What's the intent to recreate monitor page table when shadow levels
>>> changes in sh_update_paging_modes?
>> 
>> The monitor tables have to have a different layout in different shadow
>> paging modes so that linear maps of the shadows can work properly.
>> 
> 
> On x86_64, monitor page table should always be 4 level, and we can
> uninstall the old shadow linear entry and install new shadow paging mode
> entry, why even recreate the monitor top level page?

It could probably be optimised, but is it worth it?

 -- Keir

Re: recreate monitor page table?

[Tim Deegan]

Hi :)

At 23:46 +0800 on 18 Apr (1176940011), Li, Xin B wrote:
> On x86_64, monitor page table should always be 4 level, and we can
> uninstall the old shadow linear entry and install new shadow paging mode
> entry, why even recreate the monitor top level page?

We could have made a routine to adjust the layout of the monitor table
given the old and new modes, but it would have to understand two modes
at once, which nothing else in multi.c does.  It would also reproduce 
code that's already in sh_make_monitor_table and sh_destroy_monitor_table.
Since we don't expect it to be worth optimizing this path, we just used
the existing routines.

Cheers,

Tim.  

-- 
Tim Deegan <Tim.Deegan@xensource.com>, XenSource UK Limited
Registered office c/o EC2Y 5EB, UK; company number 05334508

RE: recreate monitor page table?

[Li, Xin B]

>At 23:46 +0800 on 18 Apr (1176940011), Li, Xin B wrote:
>> On x86_64, monitor page table should always be 4 level, and we can
>> uninstall the old shadow linear entry and install new shadow 
>paging mode
>> entry, why even recreate the monitor top level page?
>
>We could have made a routine to adjust the layout of the monitor table
>given the old and new modes, but it would have to understand two modes
>at once, which nothing else in multi.c does.  It would also reproduce 
>code that's already in sh_make_monitor_table and
sh_destroy_monitor_table.
>Since we don't expect it to be worth optimizing this path, we just used
>the existing routines.


Thanks
Quite clear to me now :-)

-Xin

Re: recreate monitor page table?

[Keir Fraser]

On 18/4/07 03:13, "Li, Xin B" <xin.b.li@intel.com> wrote:

> What's the intent to recreate monitor page table when shadow levels
> changes in sh_update_paging_modes?
> -Xin

The format of the monitor table depends on the guest and/or shadow paging
levels, doesn't it? So presumably the easiest way to tackle that is to
regenerate the monitor table from scratch.

 -- Keir