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Re: [Xen-devel] [PATCH 5/9] x86/amd: Probe for legacy SSBD interfaces on boot


  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Wed, 5 Dec 2018 17:09:36 +0000
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  • Cc: Wei Liu <wei.liu2@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxx>, Brian Woods <brian.woods@xxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>
  • Delivery-date: Wed, 05 Dec 2018 17:11:52 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
  • Openpgp: preference=signencrypt

On 05/12/2018 16:50, Jan Beulich wrote:
>
>> --- a/xen/include/asm-x86/cpufeatures.h
>> +++ b/xen/include/asm-x86/cpufeatures.h
>> @@ -25,6 +25,7 @@ XEN_CPUFEATURE(XEN_SMAP,        (FSCAPINTS+0)*32+11) /* 
>> SMAP gets used by Xen it
>>  XEN_CPUFEATURE(LFENCE_DISPATCH, (FSCAPINTS+0)*32+12) /* lfence set as 
>> Dispatch Serialising */
>>  XEN_CPUFEATURE(IND_THUNK_LFENCE,(FSCAPINTS+0)*32+13) /* Use 
>> IND_THUNK_LFENCE */
>>  XEN_CPUFEATURE(IND_THUNK_JMP,   (FSCAPINTS+0)*32+14) /* Use IND_THUNK_JMP */
>> +XEN_CPUFEATURE(LEGACY_SSBD,     (FSCAPINTS+0)*32+15) /* LS_CFG or 
>> VIRT_SPEC_CTRL available for SSBD */
> ... here, but I still will need to see how this gets used before
> giving my ack here. Additionally I can see "legacy" as a suitable
> name for the LS_CFG approach, but does this also fit the
> VIRT_SPEC_CTRL one?

In practice, VIRT_SPEC_CTRL means "your hypervisor is using LS_CFG on
your behalf".

As to the joint meaning, that's because it is the most appropriate (i.e.
simple) way to structure the code.

>
> One other question: There's now redundant code in init_amd()
> handling opt_ssbd. Would it not fit here to remove/replace that?

The code in init_amd() only becomes redundant in patch 7, and that is
where it is removed.

~Andrew

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