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Re: [PATCH v2 4/9] x86/spec-ctrl: Don't use spec_ctrl_{enter,exit}_idle() for S3
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 31 Jan 2022 11:15:33 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 31 Jan 2022 10:15:45 +0000
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On 28.01.2022 14:29, Andrew Cooper wrote:
> 'idle' here refers to hlt/mwait. The S3 path isn't an idle path - it is a
> platform reset.
>
> Conditionally clearing IBRS and flushing the store buffers on the way down is
> a waste of time.
I can buy this for the flushing aspect; I'm less certain about the clearing
of IBRS: Whether the act of clearing is slower than the performance price
of running with it enabled is unknown, I suppose?
> Furthermore, we want to load default_xen_mcu_opt_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.
I'll assume from your reply that you've adjusted the description as well.
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Preferably with the statement above softened a little:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Jan
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