Re: [Xen-ia64-devel] [RFC][PATCH] [RESEND] support special guest optimisations in the hypervisor

[Alex Williamson <alex.williamson@xxxxxx>]

On Thu, 2007-06-28 at 14:52 +0200, Dietmar Hahn wrote:
> Hi,
> 
> attached to this mail are 2 patches:
> - opt_feature_xen.patch
>   implements the new hypercall  __HYPERVISOR_opt_feature in the hypervisor.
> - opt_feature_linux.patch
>   implements the usage of the hypercall.
> 
> The xen - patch has real effects in vcpu_translate() on inserting identity 
> mappings in the vhpt/tlb. I'am not sure about some performance impacts.
> But without such a patch correct future protection key handling is impossible.
> 
> Please send comments or commit!

Hi Dietmar,

   I have a couple comments.  First, a minor point, but isn't an
"identity mapping" feature a little vague?  Do we specifically want a
"region 7 identity mapping" feature bit?  Second, the HVM code recently
added support for the for the guest to identify itself using an ACPI
_OSI call.  This has some similarity with what this patch is trying to
do for PV domains.  I wonder if it might be appropriate to make the HVM
side explicitly set feature bits so we don't have one method of setting
features on HVM and another on PV.  Maybe set_os_type() could make the
appropriate domain_opt_feature() calls for HVM domains(?).  The PV
domains should of course use the hypercall interface for setting
features.  Thanks,

        Alex

-- 
Alex Williamson                             HP Open Source & Linux Org.


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