Re: [PATCH v3 1/6] KVM: arm64: unify code to prepare traps

[Shaoqin Huang <shahuang@redhat.com>]

Hi Sebastian,

On 5/14/24 15:22, Sebastian Ott wrote:
> There are 2 functions to calculate traps via HCR_EL2:
> * kvm_init_sysreg() called via KVM_RUN (before the 1st run or when
>    the pid changes)
> * vcpu_reset_hcr() called via KVM_ARM_VCPU_INIT
> 
> To unify these 2 and to support traps that are dependent on the
> ID register configuration, move the code from vcpu_reset_hcr()
> to sys_regs.c and call it via kvm_init_sysreg().
> 
> We still have to keep the non-FWB handling stuff in vcpu_reset_hcr().
> Also the initialization with HCR_GUEST_FLAGS is kept there but guarded
> by !vcpu_has_run_once() to ensure that previous calculated values
> don't get overwritten.
> 
> While at it rename kvm_init_sysreg() to kvm_calculate_traps() to
> better reflect what it's doing.
> 
> Signed-off-by: Sebastian Ott <sebott@redhat.com>
> ---
>   arch/arm64/include/asm/kvm_emulate.h | 40 +++++++---------------------
>   arch/arm64/include/asm/kvm_host.h    |  2 +-
>   arch/arm64/kvm/arm.c                 |  2 +-
>   arch/arm64/kvm/sys_regs.c            | 34 +++++++++++++++++++++--
>   4 files changed, 43 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 501e3e019c93..84dc3fac9711 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -69,39 +69,17 @@ static __always_inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu)
>   
>   static inline void vcpu_reset_hcr(struct kvm_vcpu *vcpu)
>   {
> -	vcpu->arch.hcr_el2 = HCR_GUEST_FLAGS;
> -	if (has_vhe() || has_hvhe())
> -		vcpu->arch.hcr_el2 |= HCR_E2H;
> -	if (cpus_have_final_cap(ARM64_HAS_RAS_EXTN)) {
> -		/* route synchronous external abort exceptions to EL2 */
> -		vcpu->arch.hcr_el2 |= HCR_TEA;
> -		/* trap error record accesses */
> -		vcpu->arch.hcr_el2 |= HCR_TERR;
> -	}
> +	if (!vcpu_has_run_once(vcpu))
> +		vcpu->arch.hcr_el2 = HCR_GUEST_FLAGS;

Could you give more explaination in your comments about why we still 
keep the non-FWB handling in vcpu_reset_hcr()? That would be better for 
understanding the special case.

Thanks,
Shaoqin

>   
> -	if (cpus_have_final_cap(ARM64_HAS_STAGE2_FWB)) {
> -		vcpu->arch.hcr_el2 |= HCR_FWB;
> -	} else {
> -		/*
> -		 * For non-FWB CPUs, we trap VM ops (HCR_EL2.TVM) until M+C
> -		 * get set in SCTLR_EL1 such that we can detect when the guest
> -		 * MMU gets turned on and do the necessary cache maintenance
> -		 * then.
> -		 */
> +	/*
> +	 * For non-FWB CPUs, we trap VM ops (HCR_EL2.TVM) until M+C
> +	 * get set in SCTLR_EL1 such that we can detect when the guest
> +	 * MMU gets turned on and do the necessary cache maintenance
> +	 * then.
> +	 */
> +	if (!cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
>   		vcpu->arch.hcr_el2 |= HCR_TVM;
> -	}
> -
> -	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
> -	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
> -		vcpu->arch.hcr_el2 |= HCR_TID4;
> -	else
> -		vcpu->arch.hcr_el2 |= HCR_TID2;
> -
> -	if (vcpu_el1_is_32bit(vcpu))
> -		vcpu->arch.hcr_el2 &= ~HCR_RW;
> -
> -	if (kvm_has_mte(vcpu->kvm))
> -		vcpu->arch.hcr_el2 |= HCR_ATA;
>   }
>   
>   static inline unsigned long *vcpu_hcr(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 8170c04fde91..212ae77eefaf 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -1122,7 +1122,7 @@ int __init populate_nv_trap_config(void);
>   bool lock_all_vcpus(struct kvm *kvm);
>   void unlock_all_vcpus(struct kvm *kvm);
>   
> -void kvm_init_sysreg(struct kvm_vcpu *);
> +void kvm_calculate_traps(struct kvm_vcpu *);
>   
>   /* MMIO helpers */
>   void kvm_mmio_write_buf(void *buf, unsigned int len, unsigned long data);
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 9996a989b52e..6b217afb4e8e 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -797,7 +797,7 @@ int kvm_arch_vcpu_run_pid_change(struct kvm_vcpu *vcpu)
>   	 * This needs to happen after NV has imposed its own restrictions on
>   	 * the feature set
>   	 */
> -	kvm_init_sysreg(vcpu);
> +	kvm_calculate_traps(vcpu);
>   
>   	ret = kvm_timer_enable(vcpu);
>   	if (ret)
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 22b45a15d068..41741bf4d2b2 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -4041,11 +4041,33 @@ int kvm_vm_ioctl_get_reg_writable_masks(struct kvm *kvm, struct reg_mask_range *
>   	return 0;
>   }
>   
> -void kvm_init_sysreg(struct kvm_vcpu *vcpu)
> +static void vcpu_set_hcr(struct kvm_vcpu *vcpu)
>   {
>   	struct kvm *kvm = vcpu->kvm;
>   
> -	mutex_lock(&kvm->arch.config_lock);
> +	if (has_vhe() || has_hvhe())
> +		vcpu->arch.hcr_el2 |= HCR_E2H;
> +	if (cpus_have_final_cap(ARM64_HAS_RAS_EXTN)) {
> +		/* route synchronous external abort exceptions to EL2 */
> +		vcpu->arch.hcr_el2 |= HCR_TEA;
> +		/* trap error record accesses */
> +		vcpu->arch.hcr_el2 |= HCR_TERR;
> +	}
> +
> +	if (cpus_have_final_cap(ARM64_HAS_STAGE2_FWB))
> +		vcpu->arch.hcr_el2 |= HCR_FWB;
> +
> +	if (cpus_have_final_cap(ARM64_HAS_EVT) &&
> +	    !cpus_have_final_cap(ARM64_MISMATCHED_CACHE_TYPE))
> +		vcpu->arch.hcr_el2 |= HCR_TID4;
> +	else
> +		vcpu->arch.hcr_el2 |= HCR_TID2;
> +
> +	if (vcpu_el1_is_32bit(vcpu))
> +		vcpu->arch.hcr_el2 &= ~HCR_RW;
> +
> +	if (kvm_has_mte(vcpu->kvm))
> +		vcpu->arch.hcr_el2 |= HCR_ATA;
>   
>   	/*
>   	 * In the absence of FGT, we cannot independently trap TLBI
> @@ -4054,6 +4076,14 @@ void kvm_init_sysreg(struct kvm_vcpu *vcpu)
>   	 */
>   	if (!kvm_has_feat(kvm, ID_AA64ISAR0_EL1, TLB, OS))
>   		vcpu->arch.hcr_el2 |= HCR_TTLBOS;
> +}
> +
> +void kvm_calculate_traps(struct kvm_vcpu *vcpu)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	mutex_lock(&kvm->arch.config_lock);
> +	vcpu_set_hcr(vcpu);
>   
>   	if (cpus_have_final_cap(ARM64_HAS_HCX)) {
>   		vcpu->arch.hcrx_el2 = HCRX_GUEST_FLAGS;

-- 
Shaoqin