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Re: [PATCH v4 3/3] amd/msr: implement VIRT_SPEC_CTRL for HVM guests using legacy SSBD
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 2 May 2022 08:11:54 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Mon, 02 May 2022 06:12:02 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 29.04.2022 17:49, Roger Pau Monné wrote:
> On Fri, Apr 29, 2022 at 12:59:58PM +0200, Jan Beulich wrote:
>> On 27.04.2022 12:47, Roger Pau Monne wrote:
>>> @@ -3138,6 +3140,9 @@ void vmentry_virt_spec_ctrl(void)
>>>
>>> if ( cpu_has_virt_ssbd )
>>> wrmsr(MSR_VIRT_SPEC_CTRL, current->arch.msrs->virt_spec_ctrl.raw,
>>> 0);
>>> + else
>>> + amd_set_legacy_ssbd(current->arch.msrs->virt_spec_ctrl.raw &
>>> + SPEC_CTRL_SSBD);
>>
>> Would seem cheaper to use !val here (and then val for symmetry in
>> the other function).
>
> I could even use !opt_ssbd, and that would be more similar to what's
> done in vmexit_virt_spec_ctrl?
Might be an option, yet when using "val" there as well I don't see
benefit similarity-wise. Using a local variable would imo still be
cheaper than accessing a global one. But that's a matter of taste
to a fair degree, so I'll leave it to you - all I'd really prefer
to have is the functions using as similar / symmetric as possible
conditions.
Jan
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