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Re: [PATCH] x86/hvm: Remove callback from paging->flush_tlb() hook
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 18 Nov 2021 11:45:26 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 18 Nov 2021 10:45:43 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 17.11.2021 19:26, Andrew Cooper wrote:
> TLB flushing is a hotpath, and function pointer calls are
> expensive (especially under repoline) for what amounts to an identity
> transform on the data. Just pass the vcpu_bitmap bitmap directly.
>
> As we use NULL for all rather than none, introduce a flush_vcpu() helper to
> avoid the risk of logical errors from opencoding the expression. This also
> means the viridian callers can avoid writing an all-ones bitmap for the
> flushing logic to consume.
I think you want to clarify that you convert only one of the two ways of
specifying "all". The other (HV_GENERIC_SET_ALL as consumed by
hv_vpset_to_vpmask()) could also be converted, but this would be a bit
more involved. I have no idea which of the two Windows would typically
use, nor why there are two mechanisms in the first place.
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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