MTRR and cache programming in Xen

MTRR and cache programming in Xen

[ayush ruia]

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Hi all,
Hoping that you could answer a few of my queries regarding cache properties
for Xen.

Is there any support from Xen for supporting MTRRs or any similar caching
mechanisms such as PAT? How does Xen handle I/O ranges because different
memory regions may have different caching requirements and any domU can be
allocated I/O regions? Is the control on x86 only on individual page basis?
How does that reflect in terms of Intel VT-x and Intel VT-d extensions and
VMCS structures?

Any pointers regarding the above will be very helpful and highly
appreciated.


Thanks and Regards,
Ayush Ruia.

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Re: MTRR and cache programming in Xen

[Jan Beulich]

>>> On 13.01.15 at 02:59, <ayushruia@gmail.com> wrote:
> Is there any support from Xen for supporting MTRRs or any similar caching
> mechanisms such as PAT? How does Xen handle I/O ranges because different
> memory regions may have different caching requirements and any domU can be
> allocated I/O regions? Is the control on x86 only on individual page basis?
> How does that reflect in terms of Intel VT-x and Intel VT-d extensions and
> VMCS structures?
> 
> Any pointers regarding the above will be very helpful and highly
> appreciated.

Please forgive the question, but did you really make any attempt
to find the code of interest? I'm rather getting the impression that
you try to abuse the list to save you some time looking around...

Jan

Re: MTRR and cache programming in Xen

[Ian Campbell]

On Mon, 2015-01-12 at 19:59 -0600, ayush ruia wrote:
> Hi all,
> Hoping that you could answer a few of my queries regarding cache
> properties for Xen.
> 
> Is there any support from Xen for supporting MTRRs or any similar
> caching mechanisms such as PAT? How does Xen handle I/O ranges because
> different memory regions may have different caching requirements and
> any domU can be allocated I/O regions? Is the control on x86 only on
> individual page basis? How does that reflect in terms of Intel VT-x
> and Intel VT-d extensions and VMCS structures?
> 
> 
> Any pointers regarding the above will be very helpful and highly
> appreciated.

grep'ping for some of those keywords in the Xen source code and search
for "Xen $keyword" on a search engine should give you a reasonable
starting point.

See also http://wiki.xen.org/wiki/Asking_Xen_Devel_Questions

Ian.

Re: MTRR and cache programming in Xen

[ayush ruia]

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Hi all,
I apologize for giving the wrong impression. While I agree that I was
trying to avoid going through the source code. I had previously looked
online and found that that Xen did not support MTRR. I guess that is true.
Anyways, thanks for the feedback. I should be more careful in asking
question in the mailing list. :) Probably culturing a bad habit due to
overuse of stackoverflow.com, which thrives on this model. :)

Thanks and Regards,
Ayush Ruia.

Regards,
Ayush Ruia.

On Tue, Jan 13, 2015 at 4:36 AM, Ian Campbell <Ian.Campbell@citrix.com>
wrote:

> On Mon, 2015-01-12 at 19:59 -0600, ayush ruia wrote:
> > Hi all,
> > Hoping that you could answer a few of my queries regarding cache
> > properties for Xen.
> >
> > Is there any support from Xen for supporting MTRRs or any similar
> > caching mechanisms such as PAT? How does Xen handle I/O ranges because
> > different memory regions may have different caching requirements and
> > any domU can be allocated I/O regions? Is the control on x86 only on
> > individual page basis? How does that reflect in terms of Intel VT-x
> > and Intel VT-d extensions and VMCS structures?
> >
> >
> > Any pointers regarding the above will be very helpful and highly
> > appreciated.
>
> grep'ping for some of those keywords in the Xen source code and search
> for "Xen $keyword" on a search engine should give you a reasonable
> starting point.
>
> See also http://wiki.xen.org/wiki/Asking_Xen_Devel_Questions
>
> Ian.
>
>
>

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Re: MTRR and cache programming in Xen

[Jan Beulich]

>>> On 13.01.15 at 12:50, <ayushruia@gmail.com> wrote:
> I apologize for giving the wrong impression. While I agree that I was
> trying to avoid going through the source code. I had previously looked
> online and found that that Xen did not support MTRR. I guess that is true.

It's not - neither for Xen's own use of the hardware, nor for
emulating respective behavior for HVM guests and supplying
suitable interfaces for PV ones.

Jan