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... M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
