On 11/5/2015 6:48 AM, Christoffer Dall wrote:
> On Fri, Oct 30, 2015 at 02:56:32PM -0700, Mario Smarduch wrote:
>> This patch tracks vfp/simd hardware state with a vcpu lazy flag. vCPU lazy
>> flag is set on guest access and traps to vfp/simd hardware switch handler. On
>> vm-enter if lazy flag is set skip trap enable and save host fpexc. On
>> vm-exit if flag is set skip hardware context switch and return to host with
>> guest context. In vcpu_put check if vcpu lazy flag is set, and execute a
>> hardware context switch to restore host.
>>
>> Also some arm64 field and empty function are added to compile for arm64.
>>
>> Signed-off-by: Mario Smarduch <m.smarduch@xxxxxxxxxxx>
>> ---
>> arch/arm/include/asm/kvm_host.h | 1 +
>> arch/arm/kvm/arm.c | 6 ++++
>> arch/arm/kvm/interrupts.S | 60 ++++++++++++++++++++++++++++-----------
>> arch/arm/kvm/interrupts_head.S | 14 +++++----
>> arch/arm64/include/asm/kvm_host.h | 4 +++
>> 5 files changed, 63 insertions(+), 22 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index f1bf551..a9e86e0 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -227,6 +227,7 @@ int kvm_perf_teardown(void);
>> void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>>
>> struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
>> +void kvm_restore_host_vfp_state(struct kvm_vcpu *);
>>
>> static inline void kvm_arch_hardware_disable(void) {}
>> static inline void kvm_arch_hardware_unsetup(void) {}
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index dc017ad..11a56fe 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -296,6 +296,12 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>> {
>> /*
>> + * If fp/simd registers are dirty save guest, restore host before
>
> If the fp/simd registers are dirty, then restore the host state before
I'd drop 'releasing the cpu', the vcpu thread may be returning to
user mode.
>
>> + * releasing the cpu.
>> + */
>> + if (vcpu->arch.vfp_dirty)
>> + kvm_restore_host_vfp_state(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
>> * optimized make_all_cpus_request path.
>> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
>> index 900ef6d..ca25314 100644
>> --- a/arch/arm/kvm/interrupts.S
>> +++ b/arch/arm/kvm/interrupts.S
>> @@ -28,6 +28,32 @@
>> #include "interrupts_head.S"
>>
>> .text
>> +/**
>> + * void kvm_restore_host_vfp_state(struct vcpu *vcpu) - Executes lazy
>
> nit: Can you move the multi-line description of the function into a
> separate paragraph?
Sure.
>
>> + * fp/simd switch, saves the guest, restores host. Called from host
>> + * mode, placed outside of hyp region start/end.
>
> Put the description in a separate paragraph and get rid of the "executes
> lazy fp/simd swithch" part, that doesn't help understanding. Just say
> that this funciton restores the host state.
Sure.
>
>> + */
>> +ENTRY(kvm_restore_host_vfp_state)
>> +#ifdef CONFIG_VFPv3
>> + push {r4-r7}
>> +
>> + add r7, vcpu, #VCPU_VFP_GUEST
>> + store_vfp_state r7
>> +
>> + add r7, vcpu, #VCPU_VFP_HOST
>> + ldr r7, [r7]
>> + restore_vfp_state r7
>> +
>> + ldr r3, [vcpu, #VCPU_VFP_HOST_FPEXC]
>> + VFPFMXR FPEXC, r3
>> +
>> + mov r3, #0
>> + strb r3, [vcpu, #VCPU_VFP_DIRTY]
>> +
>> + pop {r4-r7}
>> +#endif
>> + bx lr
>> +ENDPROC(kvm_restore_host_vfp_state)
>>
>> __kvm_hyp_code_start:
>> .globl __kvm_hyp_code_start
>> @@ -119,11 +145,16 @@ ENTRY(__kvm_vcpu_run)
>> @ If the host kernel has not been configured with VFPv3 support,
>> @ then it is safer if we deny guests from using it as well.
>> #ifdef CONFIG_VFPv3
>> - @ Set FPEXC_EN so the guest doesn't trap floating point instructions
>> + @ fp/simd register file has already been accessed, so skip host fpexc
>> + @ save and access trap enable.
>> + vfp_inlazy_mode r7, skip_guest_vfp_trap
>
> So, why do we need to touch this register at all on every CPU exit?
>
> Is it not true that we can only be in one of two state:
> 1) The register file is not dirty (not touched by the guest) and we
> should trap
> 2) The register file is dirty, and we should not trap to EL2?
>
> Only in the first case do we need to set the FPEXC, and couldn't we just
> do that on vcpu_load and git rid of all this? (except HCPTR_TCP which
> we still need to adjust).
I'm trying to think what happens if you're preempted after you saved
the FPEXC and set the FPEXC_EN bit in kvm_arch_vcpu_load(). Could some
thread pick up a bad FPEXC? May be possible to undo in the vcpu_put().
>
>> +
>> VFPFMRX r2, FPEXC @ VMRS
>> - push {r2}
>> + str r2, [vcpu, #VCPU_VFP_HOST_FPEXC]
>> orr r2, r2, #FPEXC_EN
>> VFPFMXR FPEXC, r2 @ VMSR
>> + set_hcptr vmentry, (HCPTR_TCP(10) | HCPTR_TCP(11))
>> +skip_guest_vfp_trap:
>> #endif
>>
>> @ Configure Hyp-role
>> @@ -131,7 +162,7 @@ ENTRY(__kvm_vcpu_run)
>>
>> @ Trap coprocessor CRx accesses
>> set_hstr vmentry
>> - set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
>> + set_hcptr vmentry, (HCPTR_TTA)
>
> based on the above I think you can rework this to set the mask based on
> the dirty flag and only hit the HCPTR once.
Not sure how to do this, tracing always needs to be enabled, and it's
independent of FP dirty state.
>
>> set_hdcr vmentry
>>
>> @ Write configured ID register into MIDR alias
>> @@ -170,22 +201,15 @@ __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))
>>
>> #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}
>> + @ If fp/simd not dirty, restore FPEXC which we clobbered on entry.
>> + @ Otherwise return with guest FPEXC, later saved in vcpu_put.
>> + vfp_inlazy_mode r2, skip_restore_host_fpexc
>> + ldr r2, [vcpu, #VCPU_VFP_HOST_FPEXC]
>
> I think you should always just restore in this in vcpu_put instead of
> hitting on this all the time.
True, I was thinking of stack unwinding from older code.
>
>> VFPFMXR FPEXC, r2
>> -#else
>> -after_vfp_restore:
>> +skip_restore_host_fpexc:
>> #endif
>>
>> @ Reset Hyp-role
>> @@ -485,6 +509,10 @@ switch_to_guest_vfp:
>> @ NEON/VFP used. Turn on VFP access.
>> set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11))
>>
>> + @ set lazy mode flag, switch hardware context on vcpu_put
>> + mov r1, #1
>> + strb r1, [vcpu, #VCPU_VFP_DIRTY]
>> +
>> @ Switch VFP/NEON hardware state to the guest's
>> add r7, r0, #VCPU_VFP_HOST
>> ldr r7, [r7]
>> diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
>> index 51a5950..34e71ee 100644
>> --- a/arch/arm/kvm/interrupts_head.S
>> +++ b/arch/arm/kvm/interrupts_head.S
>> @@ -593,10 +593,8 @@ ARM_BE8(rev r6, r6 )
>> * (hardware reset value is 0). Keep previous value in r2.
>> * An ISB is emited on vmexit/vmtrap, but executed on vmexit only if
>> * VFP wasn't already enabled (always executed on vmtrap).
>> - * If a label is specified with vmexit, it is branched to if VFP wasn't
>> - * enabled.
>> */
>> -.macro set_hcptr operation, mask, label = none
>> +.macro set_hcptr operation, mask
>> mrc p15, 4, r2, c1, c1, 2
>> ldr r3, =\mask
>> .if \operation == vmentry
>> @@ -611,13 +609,17 @@ ARM_BE8(rev r6, r6 )
>> beq 1f
>> .endif
>> isb
>> - .if \label != none
>> - b \label
>> - .endif
>> 1:
>> .endif
>> .endm
>>
>> +/* Checks if VFP/SIMD dirty flag is set, if it is branch to label. */
>> +.macro vfp_inlazy_mode, reg, label
>
> Again, I don't find this "in lazy mode" to mean that we've now switched
> to the guest's VFP state intuitive or logical.
>
> How about vfp_skip_if_dirty ?
Yes sounds good.
>
>> + ldr \reg, [vcpu, #VCPU_VFP_DIRTY]
>> + cmp \reg, #1
>> + beq \label
>> +.endm
>> +
>> /* Configures the HDCR (Hyp Debug Configuration Register) on entry/return
>> * (hardware reset value is 0) */
>> .macro set_hdcr operation
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 4562459..26a2347 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -157,6 +157,9 @@ struct kvm_vcpu_arch {
>> /* Interrupt related fields */
>> u64 irq_lines; /* IRQ and FIQ levels */
>>
>> + /* fp/simd dirty flag true if guest accessed register file */
>> + bool vfp_dirty;
>> +
>> /* Cache some mmu pages needed inside spinlock regions */
>> struct kvm_mmu_memory_cache mmu_page_cache;
>>
>> @@ -248,6 +251,7 @@ static inline void kvm_arch_hardware_unsetup(void) {}
>> static inline void kvm_arch_sync_events(struct kvm *kvm) {}
>> static inline void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu) {}
>> static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
>> +static inline void kvm_restore_host_vfp_state(struct kvm_vcpu *vcpu) {}
>>
>> void kvm_arm_init_debug(void);
>> void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
>> --
>> 1.9.1
>>
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