On Tue, Sep 13, 2016 at 06:26:12PM +0200, Paolo Bonzini wrote:
>
>
> On 13/09/2016 16:58, Greg KH wrote:
> > [adding stable@ as this is a stable issue, not a 'normal' issue]
> >
> > On Tue, Sep 13, 2016 at 03:51:00PM +0100, Matt Fleming wrote:
> >> Folks,
> >>
> >> While hunting down a performance issue involving KVM I was surprised
> >> to see "native_set_debugreg()" as the first entry in `perf top`.
> >>
> >> Digging deeper, it looks as though the following patches were applied
> >> in the wrong order in -stable. This is the order as they appear in
> >> Linus' tree,
> >>
> >> [0] commit 4e422bdd2f84 ("KVM: x86: fix missed hardware breakpoints")
> >> [1] commit 172b2386ed16 ("KVM: x86: fix missed hardware breakpoints")
> >> [2] commit 70e4da7a8ff6 ("KVM: x86: fix root cause for missed hardware
> >> breakpoints")
> >>
> >> but this is the order for linux-4.4.y
> >>
> >> [1] commit fc90441e728a ("KVM: x86: fix missed hardware breakpoints")
> >> [2] commit 25e8618619a5 ("KVM: x86: fix root cause for missed hardware
> >> breakpoints")
> >> [0] commit 0f6e5e26e68f ("KVM: x86: fix missed hardware breakpoints")
> >>
> >> The upshot is that KVM_DEBUGREG_RELOAD is always set when returning
> >> from kvm_arch_vcpu_load() in stable, but not in Linus' tree.
> >
> > How would applying these in a different order cause breakage?
>
> [2] is reverting [0]+[1]. Stable is not due to the different order.
Really? Are you sure that [0] and [1] isn't just the same commit? It
looks like that to me.
> > And if this is a problem, can you please send me a patch to fix it up?
>
> Yup, on the way.
thanks,
greg k-h
