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 <m.smarduch@xxxxxxxxxxx>
>> ---
>> 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
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