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Re: [PATCH v2 6/6] x86: limit amount of INT3 in IND_THUNK_*

  • To: Jan Beulich <jbeulich@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
  • Date: Thu, 8 Oct 2020 18:35:41 +0200
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  • Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
  • Delivery-date: Thu, 08 Oct 2020 16:36:05 +0000
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On Mon, Sep 28, 2020 at 02:32:24PM +0200, Jan Beulich wrote:
> There's no point having every replacement variant to also specify the
> INT3 - just have it once in the base macro. When patching, NOPs will get
> inserted, which are fine to speculate through (until reaching the INT3).
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

> ---
> I also wonder whether the LFENCE in IND_THUNK_RETPOLINE couldn't be
> replaced by INT3 as well. Of course the effect will be marginal, as the
> size of the thunk will still be 16 bytes when including tail padding
> resulting from alignment.

I think Andrew is the best one to have an opinion on this.

Thanks, Roger.



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