On Wed, Jul 26, 2017 at 03:31:48PM +1000, Paul Mackerras wrote:
> commit 4c3bb4ccd074e1a0552078c0bf94c662367a1658 upstream.
>
> This restores several special-purpose registers (SPRs) to sane values
> on guest exit that were missed before.
>
> TAR and VRSAVE are readable and writable by userspace, and we need to
> save and restore them to prevent the guest from potentially affecting
> userspace execution (not that TAR or VRSAVE are used by any known
> program that run uses the KVM_RUN ioctl). We save/restore these
> in kvmppc_vcpu_run_hv() rather than on every guest entry/exit.
>
> FSCR affects userspace execution in that it can prohibit access to
> certain facilities by userspace. We save/restore it like we do
> for TAR and VRSAVE.
>
> PSPB is normally 0. We restore it to 0 on guest exit to prevent
> userspace taking advantage of the guest having set it non-zero
> (which would allow userspace to set its SMT priority to high).
>
> UAMOR is normally 0. We restore it to 0 on guest exit to prevent
> the AMR from being used as a covert channel between userspace
> processes, since the AMR is not context-switched at present.
>
> [paulus@xxxxxxxxxx - removed IAMR bits that are only needed on POWER9;
> adjusted FSCR save/restore for lack of fscr field in thread_struct.]
>
> 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 | 13 +++++++++++--
> arch/powerpc/kvm/book3s_hv_rmhandlers.S | 2 ++
> 2 files changed, 13 insertions(+), 2 deletions(-)
Now applied, thanks.
greg k-h