Re: [PATCH v2] x86/ibpb: Skip IBPB when we switch back to same user process

[Woodhouse, David]

On Sun, 2018-01-28 at 10:56 +0100, Ingo Molnar wrote:
> 
> What tree is this patch against? It doesn't apply to linus's latest, nor toÂ
> tip:master.

It's in my tree at
Âhttp://git.infradead.org/users/dwmw2/linux-retpoline.git/shortlog/refs/heads/ibpb
which is gradually being finalized and flushed via tip/x86/pti.

The IBPB on context switch parts are currently the first three patches
there, which roughly suggests they might be the next to get sent out
for real, if we have reached a consensus. The three patches there
probably want collapsing into one, but I've left them as-is for now
while we're discussing it.

The other thing that's next on the list is exposing the MSRs to guests.
The IBPB one is fairly simple, and Karim is working on exposing IBRS to
guests too, using Paolo's per-vCPU MSR bitmap to do the same trick
we've done in Xen, to expose it only after the guest first touches it
(to avoid the cost of swapping it when it's always 0ââ0 in the common
case). I think Ashok was talking about doing the same thing? We'll see
who gets there first :)

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