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Re: [PATCH v2 4/9] x86/spec-ctrl: Don't use spec_ctrl_{enter,exit}_idle() for S3


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>
  • Date: Mon, 31 Jan 2022 14:24:24 +0000
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  • Cc: Roger Pau Monne <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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  • Thread-topic: [PATCH v2 4/9] x86/spec-ctrl: Don't use spec_ctrl_{enter,exit}_idle() for S3

On 31/01/2022 11:23, Andrew Cooper wrote:
> On 31/01/2022 10:15, Jan Beulich wrote:
>> On 28.01.2022 14:29, Andrew Cooper wrote:
>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> Preferably with the statement above softened a little:
>> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
> Thanks.

Commit message now reads:

---8<---
'idle' here refers to hlt/mwait.  The S3 path isn't an idle path - it is a
platform reset.

We need to load default_xen_spec_ctrl unilaterally on the way back up.
Currently it happens as a side effect of X86_FEATURE_SC_MSR_IDLE or the next
return-to-guest, but that's fragile behaviour.

Conversely, there is no need to clear IBRS and flush the store buffers
on the
way down; we're microseconds away from cutting power.
---8<---

~Andrew

 


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