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Subject: Re: [RFC,05/10] x86/speculation: Add basic IBRS support
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From:   Arjan van de Ven <arjan@linux.intel.com>
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Date:   Mon, 29 Jan 2018 17:32:05 -0800
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On 1/29/2018 4:23 PM, Linus Torvalds wrote:
>
> Why do you even _care_ about the guest, and how it acts wrt Skylake?
> What you should care about is not so much the guests (which do their
> own thing) but protect guests from each other, no?

the most simple solution is that we set the internal feature bit in Linux
to turn on the "stuff the RSB" workaround is we're on a SKL *or* as a guest in a VM.

The stuffing is not free, but it's also not insane either... so if it's turned on in guests,
the impact is still limited, while bare metal doesn't need it at all