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> _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
