Re: Re: "Barry Silverman": Setting GDT entries for Thread Local Storage

[Zachary Amsden <zamsden@cisco.com>]

Keir Fraser wrote:

>The vsyscall interface happens to sit at the top of virtual memory in
>native Linux, I think mainly because the vsyscall page is allocated
>using the Linux 'fixmap' mechanism.
>  
>
>However, the address of the vsyscall interface is passed to
>applications as part of the ELF-loading protocol. It should therefore
>be possible to map the vsyscall stubs to a different virtual address
>in Xenolinux (Fingers crossed!).
>  
>
I think that might work, but it seems somewhat unnecessary.  Does Xen 
use the very top part of VM space for any special purpose - e.g. stack?  
Why not just make Xen itself a kernel fixmap entry to avoid collisions?

>I hope we don't have to go down a 'map Xen to guest-specific location'
>kind of route. I think that position-independent code in x86 is likely
>to perform below-par (no PC-relative addressing; allocating a base
>register is painful on a register-starved architecture).
>  
>
Not to mention having to deal with relocatable pointers across different 
domains!  Ugh.

Zachary Amsden
zamsden@cisco.com


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