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Re: [Xen-devel] [PATCH v1] x86/spec-ctrl: Remove EAGER_FPU when PV/HVM is disabled.
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Jin Nan Wang <jnwang@xxxxxxxx>
- Date: Mon, 5 Aug 2019 09:05:36 +0000
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- Cc: Jan Beulich <JBeulich@xxxxxxxx>, "roger.pau@xxxxxxxxxx" <roger.pau@xxxxxxxxxx>
- Delivery-date: Mon, 05 Aug 2019 09:08:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH v1] x86/spec-ctrl: Remove EAGER_FPU when PV/HVM is disabled.
On 8/5/19 5:04 PM, Andrew Cooper wrote:
> On 05/08/2019 09:54, Jin Nan Wang wrote:
>> In commit ac3f9a72141a48d40fabfff561d5a7dc0e1b810d:
>> For one, "no-xen" should not imply "no-eager-fpu", as "eager FPU" mode
>> is to guard guests, not Xen itself, which is also expressed so by
>> print_details().
>>
>> So when spec-ctrl=pv=off,hvm=off; EAGER_FPU shouldn't be display in lines:
>> Current[Wrong]:
>> (XEN) Support for HVM VMs: EAGER_FPU MD_CLEAR
>> (XEN) Support for PV VMs: EAGER_FPU MD_CLEAR
>>
>> expectation:
>> (XEN) Support for HVM VMs: MD_CLEAR
>> (XEN) Support for PV VMs: MD_CLEAR
> Eager FPU is a performance win across the board. It will become an even
> bigger performance win when we follow in Linux's footsteps and remove
> the eager option, and associated logic.
OK.
> I don't see any value in turning it off for speculation related reasons.
Got it.
> ~Andrew
>
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