Re: [Xen-devel] [PATCH v2] x86/hvm/viridian: fix the TLB flush hypercall

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.03.16 at 15:21, <paul.durrant@xxxxxxxxxx> wrote:
> Commit b38d426a "flush remote tlbs by hypercall" add support to allow
> Windows to request flush of remote TLB via hypercall rather than IPI.
> Unfortunately it seems that this code was broken in a couple of ways:
> 
> 1) The allocation of the per-vcpu ipi mask is gated on whether the
>    domain has viridian features enabled but the call to allocate is
>    made before the toolstack has enabled those features. This results
>    in a NULL pointer dereference.
> 
> 2) One of the flush hypercall variants is a rep op, but the code
>    does not update the output data with the reps completed. Hence the
>    guest will spin repeatedly making the hypercall because it believes
>    it has uncompleted reps.
> 
> This patch fixes both of these issues as follows:
> 
> 1) The ipi mask need only be per-pcpu so it is made a per-pcpu static
>    to avoid the need for allocation.
> 
> 2) The rep complete count is updated to the rep count since the single
>    flush that Xen does covers all reps anyway.
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>


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