On 12/3/2015 7:58 AM, Marc Zyngier wrote:
> On 14/11/15 22:12, Mario Smarduch wrote:
>> This patch tracks armv7 fp/simd hardware state with a vcpu lazy flag.
>> On vcpu_load saves host fpexc and enables FP access, and later enables fp/simd
>> trapping if lazy flag is not set. On first fp/simd access trap to handler
>> to save host and restore guest context, disable trapping and set vcpu lazy
>> flag. On vcpu_put if flag is set save guest and restore host context and
>> always restore host fpexc.
>>
>> Signed-off-by: Mario Smarduch <m.smarduch@xxxxxxxxxxx>
>> ---
>> arch/arm/include/asm/kvm_host.h | 33 ++++++++++++++++++++++
>> arch/arm/kvm/arm.c | 12 ++++++++
>> arch/arm/kvm/interrupts.S | 58 +++++++++++++++++++++++----------------
>> arch/arm/kvm/interrupts_head.S | 26 +++++++++++++-----
>> arch/arm64/include/asm/kvm_host.h | 6 ++++
>> 5 files changed, 104 insertions(+), 31 deletions(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index f1bf551..8fc7a59 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -40,6 +40,38 @@
>>
>> #define KVM_MAX_VCPUS VGIC_V2_MAX_CPUS
>>
>> +/*
>> + * Reads the host FPEXC register, saves it to vcpu context and enables the
>> + * FP/SIMD unit.
>> + */
>> +#ifdef CONFIG_VFPv3
>> +#define kvm_enable_fpexc(vcpu) { \
>> + u32 fpexc = 0; \
>> + asm volatile( \
>> + "mrc p10, 7, %0, cr8, cr0, 0\n" \
>> + "str %0, [%1]\n" \
>> + "orr %0, %0, #(1 << 30)\n" \
>> + "mcr p10, 7, %0, cr8, cr0, 0\n" \
>
> Don't you need an ISB here?
Yes it does (B2.7.3) - was thinking something else but the manual is clear here.
> Also, it would be a lot nicer if this was a
> real function (possibly inlined). I don't see any real reason to make
> this a #define.
Had some trouble reconciling arm and arm64 compile making this
a function in kvm_host.h. I'll work to resolve it.
>
> Also, you're preserving a lot of the host's FPEXC bits. Is that safe?
No it may not be, should just set the enable bit.
>
>> + : "+r" (fpexc) \
>> + : "r" (&vcpu->arch.host_fpexc) \
>> + ); \
>> +}
>> +#else
>> +#define kvm_enable_fpexc(vcpu)
>> +#endif
>> +
>> +/* Restores host FPEXC register */
>> +#ifdef CONFIG_VFPv3
>> +#define kvm_restore_host_fpexc(vcpu) { \
>> + asm volatile( \
>> + "mcr p10, 7, %0, cr8, cr0, 0\n" \
>> + : : "r" (vcpu->arch.host_fpexc) \
>> + ); \
>> +}
>> +#else
>> +#define kvm_restore_host_fpexc(vcpu)
>> +#endif
>> +
>> u32 *kvm_vcpu_reg(struct kvm_vcpu *vcpu, u8 reg_num, u32 mode);
>> int __attribute_const__ kvm_target_cpu(void);
>> int kvm_reset_vcpu(struct kvm_vcpu *vcpu);
>> @@ -227,6 +259,7 @@ 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..cfc348a 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -291,10 +291,22 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
>> vcpu->arch.host_cpu_context = this_cpu_ptr(kvm_host_cpu_state);
>>
>> kvm_arm_set_running_vcpu(vcpu);
>> +
>> + /* Save and enable FPEXC before we load guest context */
>> + kvm_enable_fpexc(vcpu);
>> }
>>
>> void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
>> {
>> + /* If the fp/simd registers are dirty save guest, restore host. */
>> + if (vcpu->arch.vfp_dirty) {
>
> See my previous comment about the dirty state.
Yes that change seems to be working out fine.
>
>> + kvm_restore_host_vfp_state(vcpu);
>> + vcpu->arch.vfp_dirty = 0;
>> + }
>> +
>> + /* Restore host FPEXC trashed in vcpu_load */
>> + kvm_restore_host_fpexc(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..1ddaa89 100644
>> --- a/arch/arm/kvm/interrupts.S
>> +++ b/arch/arm/kvm/interrupts.S
>> @@ -28,6 +28,26 @@
>> #include "interrupts_head.S"
>>
>> .text
>> +/**
>> + * void kvm_restore_host_vfp_state(struct vcpu *vcpu) -
>> + * This function is called from host to save the guest, and restore host
>> + * fp/simd hardware context. It's placed outside of hyp start/end region.
>> + */
>> +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
>> +
>> + pop {r4-r7}
>> +#endif
>> + bx lr
>> +ENDPROC(kvm_restore_host_vfp_state)
>>
>
> Please don't mix things that are part of the HYP code and things that
> are not in the same file. This is just asking for trouble. If that's not
> mapped into HYP, put it in a separate file.
Will do.
>
>> __kvm_hyp_code_start:
>> .globl __kvm_hyp_code_start
>> @@ -116,22 +136,22 @@ ENTRY(__kvm_vcpu_run)
>> read_cp15_state store_to_vcpu = 0
>> write_cp15_state read_from_vcpu = 1
>>
>> + set_hcptr_bits set, r4, (HCPTR_TTA)
>> @ 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
>> - VFPFMRX r2, FPEXC @ VMRS
>> - push {r2}
>> - orr r2, r2, #FPEXC_EN
>> - VFPFMXR FPEXC, r2 @ VMSR
>> + @ fp/simd register file has already been accessed, so skip trap enable.
>> + vfp_skip_if_dirty r7, skip_guest_vfp_trap
>> + set_hcptr_bits orr, r4, (HCPTR_TCP(10) | HCPTR_TCP(11))
>> +skip_guest_vfp_trap:
>> #endif
>> + set_hcptr vmentry, r4
>>
>> @ Configure Hyp-role
>> configure_hyp_role vmentry
>>
>> @ Trap coprocessor CRx accesses
>> set_hstr vmentry
>> - set_hcptr vmentry, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
>> set_hdcr vmentry
>>
>> @ Write configured ID register into MIDR alias
>> @@ -170,23 +190,8 @@ __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
>> -
>> -#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
>> + set_hcptr_bits clear, r4, (HCPTR_TTA | HCPTR_TCP(10) | HCPTR_TCP(11))
>> + set_hcptr vmexit, r4
>>
>> @ Reset Hyp-role
>> configure_hyp_role vmexit
>> @@ -483,7 +488,12 @@ switch_to_guest_vfp:
>> push {r3-r7}
>>
>> @ NEON/VFP used. Turn on VFP access.
>> - set_hcptr vmtrap, (HCPTR_TCP(10) | HCPTR_TCP(11))
>> + set_hcptr_bits clear, r4, (HCPTR_TCP(10) | HCPTR_TCP(11))
>> + set_hcptr vmtrap, r4
>> +
>> + @ set lazy mode flag, switch hardware context on vcpu_put
>> + mov r1, #1
>> + strb r1, [vcpu, #VCPU_VFP_DIRTY]
>
> You are assuming that a boolean is a byte. That's wrong, and not endian
> safe. If you want to have such a flag in a structure, use a sized type
> (u8, u16, u32). But again, I think we should rely on the trap flags to
> make decisions outside of the HYP code.
Although this is gone now, thanks for the tip very helpful.
>
> Thanks,
>
> M.
>
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