Re: [Xen-devel] [PATCH] nestedhvm: ASID emulation

[Keir Fraser <keir@xxxxxxx>]

On 13/04/2011 11:37, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:

> 
> Implement ASID emulation.
> This allows the l1 guest to run the l2 guest using hw ASID.
> 
> Signed-off-by: Christoph Egger <Christoph.Egger@xxxxxxx>

First, how much of a win is this compared with what we do currently?

Second, the two-asids-per-vcpu allocation scheme in
hvm_asid_handle_vmenter() looks broken. I mean, consider this comment:
  /* When asid generation changed last time when we were
   * were going to run l1 guest then next_asid <= nv->nv_n2asid. */
I don't see how you can assert this to be true. Arbitrary generations can
have passed, and next_asid incremented to an arbitrary value, since the last
time you allocated nv_n2asid.

I wouldn't bother fixing #2 unless there's a convincing answer for #1.

 -- Keir



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