Re: [Xen-devel] [PATCH 6/7, RFC] x86_64: basic changes for supporting compatibility mode guest

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 23/8/06 11:32 am, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:

> There was one more issue I forgot to mention: We must disable execution of
> 'syscall' in some way for compatibility domains. The question is whether to
> add respective detection code early into the syscall path (which would affect
> performance-wise all 64-bit domains) or whether to {dis,en}able the use of
> the instruction in the context switch code by updating EFER as needed
> (which would have a performance effect only when switching between
> a native and a compatibility domain, but the performance effect would likely
> be significantly greater). I'd prefer the second option, not the least because
> its implementation is significantly easier.

I'm not fussed either way really. It depends how slow it is to update EFER.
That'd be easy to check.

 -- Keir



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