Re: [Xen-devel] help -- A question about ' XENFEAT_auto_translated_physmap':

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.08.16 at 14:36, <xuquan8@xxxxxxxxxx> wrote:
> Hi Jan,
> 
> A question about ' XENFEAT_auto_translated_physmap':
> 
> In linux code, in arch/x86/xen/mmu.c,

I assume you know that I'm not a maintainer of the Linux code.

>  __xen_pgd_walk()
> {
> ....
> 
>         if (xen_feature(XENFEAT_auto_translated_physmap))
>                 return 0;
> ....
> }
> 
> 
> 
> Why xen_feature(XENFEAT_auto_translated_physmap) is true, then return 
> directly?
> If not return directly, is there any potential risk?

Well, the function is specifically there for operations (pinning/unpinning)
which are required only for the not-auto-translated case. Why would
anyone want to traverse a page table tree just to do nothing on each
of the entries?

Jan


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