From: Fabiano Rosas farosas@linux.ibm.com
commit 25edcc50d76c834479d11fcc7de46f3da4d95121 upstream.
The Facility Status and Control Register is a privileged SPR that defines the availability of some features in problem state. Since it can be written by the guest, we must restore it to the previous host value after guest exit.
This restoration is currently done by taking the value from current->thread.fscr, which in the P9 path is not enough anymore because the guest could context switch the QEMU thread, causing the guest-current value to be saved into the thread struct.
The above situation manifested when running a QEMU linked against a libc with System Call Vectored support, which causes scv instructions to be run by QEMU early during the guest boot (during SLOF), at which point the FSCR is 0 due to guest entry. After a few scv calls (1 to a couple hundred), the context switching happens and the QEMU thread runs with the guest value, resulting in a Facility Unavailable interrupt.
This patch saves and restores the host value of FSCR in the inner guest entry loop in a way independent of current->thread.fscr. The old way of doing it is still kept in place because it works for the old entry path.
Signed-off-by: Fabiano Rosas farosas@linux.ibm.com Signed-off-by: Paul Mackerras paulus@ozlabs.org Cc: Georgy Yakovlev gyakovlev@gentoo.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kvm/book3s_hv.c | 4 ++++ 1 file changed, 4 insertions(+)
--- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -3583,6 +3583,7 @@ static int kvmhv_p9_guest_entry(struct k unsigned long host_tidr = mfspr(SPRN_TIDR); unsigned long host_iamr = mfspr(SPRN_IAMR); unsigned long host_amr = mfspr(SPRN_AMR); + unsigned long host_fscr = mfspr(SPRN_FSCR); s64 dec; u64 tb; int trap, save_pmu; @@ -3726,6 +3727,9 @@ static int kvmhv_p9_guest_entry(struct k if (host_amr != vcpu->arch.amr) mtspr(SPRN_AMR, host_amr);
+ if (host_fscr != vcpu->arch.fscr) + mtspr(SPRN_FSCR, host_fscr); + msr_check_and_set(MSR_FP | MSR_VEC | MSR_VSX); store_fp_state(&vcpu->arch.fp); #ifdef CONFIG_ALTIVEC