Hi Antonios, On 9/22/2015 7:01 AM, Antonios Motakis wrote: > Hello, > > On 18-Sep-15 03:05, Mario Smarduch wrote: >> Adds code to enable fp/simd lazy switch. On each entry check if fp/simd >> registers have been switched to guest, if no set the trap flag. On trap >> switch fp/simd registers and set vfp_lazy to true and disable trapping. >> When the vcpu is about to be put, then context switch fp/simd registers >> save guest and restore host and reset the vfp_lazy state to enable trapping >> again. >> > > This description confused me a bit, since KVM on ARMv7 already exhibits > lazy switching behavior for VFP. Should the description highlight the > intended improvement in behavior? > > If I understand correctly, instead of restoring the host state on every > exit, you postpone it until the task actually gets rescheduled, right?
Yes that's right, I'll reword to highlight the changes. > >> Signed-off-by: Mario Smarduch <[email protected]> >> --- >> arch/arm/kvm/arm.c | 17 +++++++++++++++++ >> arch/arm/kvm/interrupts.S | 40 +++++++++++++++++++++++++++++----------- >> 2 files changed, 46 insertions(+), 11 deletions(-) >> >> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c >> index ce404a5..0acbb69 100644 >> --- a/arch/arm/kvm/arm.c >> +++ b/arch/arm/kvm/arm.c >> @@ -105,6 +105,20 @@ void kvm_arch_check_processor_compat(void *rtn) >> *(int *)rtn = 0; >> } >> >> +/** >> + * kvm_switch_fp_regs() - switch guest/host VFP/SIMD registers >> + * @vcpu: pointer to vcpu structure. >> + * >> + */ >> +static void kvm_switch_fp_regs(struct kvm_vcpu *vcpu) >> +{ >> +#ifdef CONFIG_ARM >> + if (vcpu->arch.vfp_lazy == 1) { >> + kvm_call_hyp(__kvm_restore_host_vfp_state, vcpu); >> + vcpu->arch.vfp_lazy = 0; >> + } >> +#endif >> +} >> >> /** >> * kvm_arch_init_vm - initializes a VM data structure >> @@ -295,6 +309,9 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) >> >> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) >> { >> + /* Check if Guest accessed VFP registers */ >> + kvm_switch_fp_regs(vcpu); >> + >> /* >> * The arch-generic KVM code expects the cpu field of a vcpu to be -1 >> * if the vcpu is no longer assigned to a cpu. This is used for the >> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S >> index 900ef6d..a47acc1 100644 >> --- a/arch/arm/kvm/interrupts.S >> +++ b/arch/arm/kvm/interrupts.S >> @@ -96,6 +96,24 @@ ENTRY(__kvm_flush_vm_context) >> bx lr >> ENDPROC(__kvm_flush_vm_context) >> >> +/** >> + * void __kvm_restore_host_vfp_state(struct vcpu *vcpu) - Executes a lazy >> + * fp/simd switch, saves the guest, restores host. >> + * >> + */ >> +ENTRY(__kvm_restore_host_vfp_state) >> + push {r3-r7} >> + >> + add r7, r0, #VCPU_VFP_GUEST >> + store_vfp_state r7 >> + >> + add r7, r0, #VCPU_VFP_HOST >> + ldr r7, [r7] >> + restore_vfp_state r7 >> + >> + pop {r3-r7} >> + bx lr >> +ENDPROC(__kvm_restore_host_vfp_state) >> >> /******************************************************************** >> * Hypervisor world-switch code >> @@ -131,7 +149,14 @@ ENTRY(__kvm_vcpu_run) >> >> @ Trap coprocessor CRx accesses >> set_hstr vmentry >> + >> + ldr r1, [vcpu, #VCPU_VFP_LAZY] >> + cmp r1, #1 >> + beq skip_guest_vfp_trap >> + >> set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)) >> +skip_guest_vfp_trap: > > I believe that HCPTR_TTA is not part of the floating point extensions. Yes you're right trap on tracing is not enabled. > >> + >> set_hdcr vmentry >> >> @ Write configured ID register into MIDR alias >> @@ -170,22 +195,12 @@ __kvm_vcpu_return: >> @ Don't trap coprocessor accesses for host kernel >> set_hstr vmexit >> set_hdcr vmexit >> - set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)), >> after_vfp_restore >> + set_hcptr vmexit, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11)) > > If you don't use the functionality of the macro to branch on change, > then maybe the functionality should also be removed from the macro. Yes, the macros needs to change. > >> >> #ifdef CONFIG_VFPv3 >> - @ Switch VFP/NEON hardware state to the host's >> - add r7, vcpu, #VCPU_VFP_GUEST >> - store_vfp_state r7 >> - add r7, vcpu, #VCPU_VFP_HOST >> - ldr r7, [r7] >> - restore_vfp_state r7 >> - >> -after_vfp_restore: >> @ Restore FPEXC_EN which we clobbered on entry >> pop {r2} >> VFPFMXR FPEXC, r2 >> -#else >> -after_vfp_restore: >> #endif >> >> @ Reset Hyp-role >> @@ -485,6 +500,9 @@ switch_to_guest_vfp: >> @ NEON/VFP used. Turn on VFP access. >> set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11)) >> >> + mov r1, #1 >> + str r1, [vcpu, #VCPU_VFP_LAZY] >> + >> @ Switch VFP/NEON hardware state to the guest's >> add r7, r0, #VCPU_VFP_HOST >> ldr r7, [r7] >> > Thanks for reviewing. - Mario -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
