Re: [PATCH 2/3] KVM: x86: hyper-v: set NoNonArchitecturalCoreSharing CPUID bit when SMT is impossible

[Paolo Bonzini]

On 23/09/19 17:37, Peter Zijlstra wrote:
>> This patch reports NoNonArchitecturalCoreSharing bit in to userspace in the
>> first case. The second case is outside of KVM's domain of responsibility
>> (as vCPU pinning is actually done by someone who manages KVM's userspace -
>> e.g. libvirt pinning QEMU threads).
> This is purely about guest<->guest MDS, right? Ie. not worse than actual
> hardware.

Even within the same guest.  If vCPU 1 is on virtual core 1 and vCPU 2
is on virtual core 2, but they can share the same physical core, core
scheduling in the guest can do nothing about it.

Paolo