Xen devel - Feb 2004 - HYPERVISOR_update_va_mapping in mm/memory.c

hi,

I am trying to guess the purpose of the calls to
HYPERVISOR_update_va_mapping in mm/memory.c, or rather why this code
(which apparently handles user space demand paging) uses a special
hypercall rather than the usual pte-update calls.

Could anyone briefly explain to me what this hypercall does, and why it
needs to be special?

thanks,
Jacob



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hi,

I am trying to guess the purpose of the calls to
HYPERVISOR_update_va_mapping in mm/memory.c, or rather why this code
(which apparently handles user space demand paging) uses a special
hypercall rather than the usual pte-update calls.

Could anyone briefly explain to me what this hypercall does, and why it
needs to be special?

thanks,
Jacob



-------------------------------------------------------
The SF.Net email is sponsored by EclipseCon 2004
Premiere Conference on Open Tools Development and Integration
See the breadth of Eclipse activity. February 3-5 in Anaheim, CA.
http://www.eclipsecon.org/osdn
_______________________________________________
Xen-devel mailing list
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https://lists.sourceforge.net/lists/listinfo/xen-devel

> hi,
> 
> I am trying to guess the purpose of the calls to
> HYPERVISOR_update_va_mapping in mm/memory.c, or rather why this code
> (which apparently handles user space demand paging) uses a special
> hypercall rather than the usual pte-update calls.
> 
> Could anyone briefly explain to me what this hypercall does, and why it
> needs to be special?
> 
> thanks,
> Jacob
It''s faster to execute than doing the same thing via the usual update
hypercall, because:
 1. The code executes one special case so it is shorter and
 straight-line.
 2. Xen modifies the specified PTE directly using the guest-provided
 mapping of that PTE. This is faster than creating a temporary mapping
 of that page in Xen''s address space.

Short answer: it''s just a performance optimisation.

 -- Keir


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The SF.Net email is sponsored by EclipseCon 2004
Premiere Conference on Open Tools Development and Integration
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