Re: [Xen-devel] Re: "Barry Silverman": Setting GDT entries for Thread Local Storage

[Zachary Amsden <zamsden@xxxxxxxxx>]

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@xxxxxxxxx


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