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* HYPERVISOR_update_va_mapping in mm/memory.c
@ 2004-02-05 17:15 Jacob Gorm Hansen
  0 siblings, 0 replies; 3+ messages in thread
From: Jacob Gorm Hansen @ 2004-02-05 17:15 UTC (permalink / raw)
  To: Xen list

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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^ permalink raw reply	[flat|nested] 3+ messages in thread
* HYPERVISOR_update_va_mapping in mm/memory.c
@ 2004-02-05 17:16 Jacob Gorm Hansen
  2004-02-05 17:43 ` Keir Fraser
  0 siblings, 1 reply; 3+ messages in thread
From: Jacob Gorm Hansen @ 2004-02-05 17:16 UTC (permalink / raw)
  To: Xen list

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

^ permalink raw reply	[flat|nested] 3+ messages in thread
* Re: HYPERVISOR_update_va_mapping in mm/memory.c
  2004-02-05 17:16 HYPERVISOR_update_va_mapping in mm/memory.c Jacob Gorm Hansen
@ 2004-02-05 17:43 ` Keir Fraser
  0 siblings, 0 replies; 3+ messages in thread
From: Keir Fraser @ 2004-02-05 17:43 UTC (permalink / raw)
  To: Jacob Gorm Hansen; +Cc: Xen list

> 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


-------------------------------------------------------
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

^ permalink raw reply	[flat|nested] 3+ messages in thread
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2004-02-05 17:16 HYPERVISOR_update_va_mapping in mm/memory.c Jacob Gorm Hansen
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2004-02-05 17:15 Jacob Gorm Hansen

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