Re: [Xen-devel] [PATCH for-4.11 00/10] x86: Improvements and fixes to Spectre handling

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 11.05.18 at 12:38, <andrew.cooper3@xxxxxxxxxx> wrote:
> In hindsight, the end result of the Spectre mitigations aren't as great as I'd
> hoped, and have several inefficiencies.  Also, the `bti=` command line option
> isn't as flexible as intended.
> 
> This series does four things:
> 
>   1) Some internal cleanup, for clarity and to help the other features
>   2) Introduce `spec-ctrl=no-pv` mode.  XenServer's performance measurements
>      see a 10% net/disk performance improvement in some production scenarios.
>   3) Introduce the ability to use IBPB-only mode for guests.  This was
>      discussed by Amazon during the Spectre work, but I don't have any
>      performance numbers to hand.
>   4) Avoid imposing IBRS mode while dom0 is booting.  This was reported by
>      Oracle on the list, and speeds up boot time on some servers by 50s.
> 
> I know this series is rather late for 4.11, but seeing as I've managed to
> complete it before 4.12 opens, it should be considered at this point, as all
> of the Spectre code is new in 4.11.
> 
> Andrew Cooper (10):
>   x86/spec_ctrl: Read MSR_ARCH_CAPABILITIES only once
>   x86/spec_ctrl: Express Xen's choice of MSR_SPEC_CTRL value as a variable
>   x86/spec_ctrl: Merge bti_ist_info and use_shadow_spec_ctrl into 
> spec_ctrl_flags
>   x86/spec_ctrl: Fold the XEN_IBRS_{SET,CLEAR} ALTERNATIVES together
>   x86/spec_ctrl: Rename bits of infrastructure to avoid NATIVE and VMEXIT
>   x86/spec_ctrl: Split X86_FEATURE_SC_MSR into PV and HVM variants
>   x86/spec_ctrl: Explicitly set Xen's default MSR_SPEC_CTRL value
>   x86/cpuid: Improvements to guest policies for speculative sidechannel 
> features
>   x86/spec_ctrl: Introduce a new `spec-ctrl=` command line argument to 
> replace `bti=`
>   x86/spec_ctrl: Elide MSR_SPEC_CTRL handling in idle context when possible

Irrespective of the small comment just sent for patch 6:
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



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