On Wed, Apr 08, 2015 at 06:16:50PM +0100, Marc Zyngier wrote: > On 08/04/15 12:40, Christoffer Dall wrote: > > On Mon, Mar 16, 2015 at 10:59:43AM +0000, Marc Zyngier wrote: > >> On VM entry, we disable access to the VFP registers in order to > >> perform a lazy save/restore of these registers. > >> > >> On VM exit, we restore access, test if we did enable them before, > >> and save/restore the guest/host registers if necessary. In this > >> sequence, the FPEXC register is always accessed, irrespective > >> of the trapping configuration. > >> > >> If the guest didn't touch the VFP registers, then the HCPTR access > >> has now enabled such access, but we're missing a barrier to ensure > >> architectural execution of the new HCPTR configuration. If the HCPTR > >> access has been delayed/reordered, the subsequent access to FPEXC > >> will cause a trap, which we aren't prepared to handle at all. > >> > >> The fix is to introduce a barrier that only takes place if the > >> guest hasn't accessed its view of the VFP registers, making > >> the access to FPEXC safe. > >> > >> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx> > >> --- > >> arch/arm/kvm/interrupts.S | 7 +++++-- > >> 1 file changed, 5 insertions(+), 2 deletions(-) > >> > >> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S > >> index 79caf79..3ac7aca 100644 > >> --- a/arch/arm/kvm/interrupts.S > >> +++ b/arch/arm/kvm/interrupts.S > >> @@ -175,10 +175,13 @@ __kvm_vcpu_return: > >> #ifdef CONFIG_VFPv3 > >> @ Save floating point registers we if let guest use them. > >> tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11)) > >> - bne after_vfp_restore > >> + beq 1f > >> + > >> + isb @ Force execution of HCPTR if we've just reenabled VFP access > >> + b after_vfp_restore > >> > >> @ Switch VFP/NEON hardware state to the host's > >> - add r7, vcpu, #VCPU_VFP_GUEST > >> +1: add r7, vcpu, #VCPU_VFP_GUEST > >> store_vfp_state r7 > >> add r7, vcpu, #VCPU_VFP_HOST > >> ldr r7, [r7] > >> -- > >> 2.1.4 > >> > > > > Reviewed-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx> > > Thanks (I must admit I completely forgot the existence of this patch...). > > I guess we can queue that for -rc1, with a Cc to stable... > yes, I tested it on TC2 (both A15 and A7) and it works like a charm. -Christoffer _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
