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

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 17/03/16 08:35, Jan Beulich wrote:
>>>> On 16.03.16 at 15:21, <paul.durrant@citrix.com> 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@citrix.com>
> Reviewed-by: Jan Beulich <jbeulich@suse.com>
>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

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