Re: [Xen-devel] [PATCH v5 5/7] x86/tlb: allow disabling the TLB clock

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.02.2020 18:43, Roger Pau Monne wrote:
> The TLB clock is helpful when running Xen on bare metal because when
> doing a TLB flush each CPU is IPI'ed and can keep a timestamp of the
> last flush.
> 
> This is not the case however when Xen is running virtualized, and the
> underlying hypervisor provides mechanism to assist in performing TLB
> flushes: Xen itself for example offers a HVMOP_flush_tlbs hypercall in
> order to perform a TLB flush without having to IPI each CPU. When
> using such mechanisms it's no longer possible to keep a timestamp of
> the flushes on each CPU, as they are performed by the underlying
> hypervisor.
> 
> Offer a boolean in order to signal Xen that the timestamped TLB
> shouldn't be used. This avoids keeping the timestamps of the flushes,
> and also forces NEED_FLUSH to always return true.
> 
> No functional change intended, as this change doesn't introduce any
> user that disables the timestamped TLB.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Reviewed-by: Wei Liu <wl@xxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>


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