Re: [Xen-devel] [PATCH v9 06/11] x86/entry: Organise the use of MSR_SPEC_CTRL at each entry/exit point

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/19/2018 08:36 AM, Andrew Cooper wrote:
> On 19/01/18 11:43, Jan Beulich wrote:
>
>>> @@ -99,6 +106,10 @@ UNLIKELY_END(realmode)
>>>  .Lvmx_vmentry_fail:
>>>          sti
>>>          SAVE_ALL
>>> +
>>> +        SPEC_CTRL_ENTRY_FROM_PV /* Req: %rsp=regs/cpuinfo Clob: acd */
>> I think the use of the PV variant here requires a comment.
> Oh.  It used to have one...  I'll try to find it.

I, in fact, meant to ask about this for a long time and always forgot.
Perhaps your comment will say more than just why a PV variant is used
here but in case it won't --- why do we have *any* mitigation here? We
are never returning to the guest, do we?

-boris

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