On Wed, Jul 26, 2017 at 09:46:15AM +1000, Paul Mackerras wrote:
> commit ca8efa1df1d15a1795a2da57f9f6aada6ed6b946 upstream.
>
> This adds code to save the values of three SPRs (special-purpose
> registers) used by userspace to control event-based branches (EBBs),
> which are essentially interrupts that get delivered directly to
> userspace. These registers are loaded up with guest values when
> entering the guest, and their values are saved when exiting the
> guest, but we were not saving the host values and restoring them
> before going back to userspace.
>
> On POWER8 this would only affect userspace programs which explicitly
> request the use of EBBs and also use the KVM_RUN ioctl, since the
> only source of EBBs on POWER8 is the PMU, and there is an explicit
> enable bit in the PMU registers (and those PMU registers do get
> properly context-switched between host and guest). On POWER9 there
> is provision for externally-generated EBBs, and these are not subject
> to the control in the PMU registers.
>
> Since these registers only affect userspace, we can save them when
> we first come in from userspace and restore them before returning to
> userspace, rather than saving/restoring the host values on every
> guest entry/exit. Similarly, we don't need to worry about their
> values on offline secondary threads since they execute in the context
> of the idle task, which never executes in userspace.
>
> Fixes: b005255e12a3 ("KVM: PPC: Book3S HV: Context-switch new POWER8 SPRs", 2014-01-08)
> Cc: stable@xxxxxxxxxxxxxxx # v3.14+
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_hv.c | 16 ++++++++++++++++
> 1 file changed, 16 insertions(+)
Now applied, thanks.
greg k-h