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Re: [PATCH v3 1/2] x86/mm: rename FLUSH_FORCE_IPI to FLUSH_NO_ASSIST


  • To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
  • Date: Wed, 25 May 2022 10:52:48 +0000
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  • Thread-topic: [PATCH v3 1/2] x86/mm: rename FLUSH_FORCE_IPI to FLUSH_NO_ASSIST

On 25/05/2022 09:13, Roger Pau Monne wrote:
> Rename the flag to better note that it's not actually forcing any IPIs
> to be issued if none is required, but merely avoiding the usage of TLB
> flush assistance (which itself can avoid the sending of IPIs to remote
> processors).
>
> No functional change expected.
>
> Requested-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> ---
> Changes since v2:
>  - New in this version.

:(  This needs reverting.

It is specific to IPIs, because of our current choice of algorithm for
freeing pagetables.

"no assist" excludes ipi-helper hypercalls which invoke
INVALIDATE_TLB_VECTOR.  Such hypercalls do exist and specifically would
be improvement that we ought to use.

Furthermore, we do want to work around the limitation that created
FLUSH_FORCE_IPI, because we absolutely do want to be able to use
hypercalls/remote TLB flushing capabilities when available.

I accept that FORCE_IPI perhaps isn't a perfect name, but it's a whole
lot less bad than NO_ASSIST.

~Andrew

 


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