Re: [PATCH v4 07/13] KVM: arm64: Add vendor hypervisor firmware register

[Oliver Upton <oupton@google.com>]

On Thu, Feb 24, 2022 at 05:25:53PM +0000, Raghavendra Rao Ananta wrote:
> Introduce the firmware register to hold the vendor specific
> hypervisor service calls (owner value 6) as a bitmap. The
> bitmap represents the features that'll be enabled for the
> guest, as configured by the user-space. Currently, this
> includes support only for Precision Time Protocol (PTP),
> represented by bit-0.
> 
> The register is also added to the kvm_arm_vm_scope_fw_regs[]
> list as it maintains its state per-VM.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/include/asm/kvm_host.h |  2 ++
>  arch/arm64/include/uapi/asm/kvm.h |  4 ++++
>  arch/arm64/kvm/guest.c            |  1 +
>  arch/arm64/kvm/hypercalls.c       | 22 +++++++++++++++++++++-
>  include/kvm/arm_hypercalls.h      |  3 +++
>  5 files changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 318148b69279..d999456c4604 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -106,10 +106,12 @@ struct kvm_arch_memory_slot {
>   *
>   * @hvc_std_bmap: Bitmap of standard secure service calls
>   * @hvc_std_hyp_bmap: Bitmap of standard hypervisor service calls
> + * @hvc_vendor_hyp_bmap: Bitmap of vendor specific hypervisor service calls
>   */
>  struct kvm_hvc_desc {
>  	u64 hvc_std_bmap;
>  	u64 hvc_std_hyp_bmap;
> +	u64 hvc_vendor_hyp_bmap;
>  };
>  
>  struct kvm_arch {
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 9a2caead7359..ed470bde13d8 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -299,6 +299,10 @@ struct kvm_arm_copy_mte_tags {
>  #define KVM_REG_ARM_STD_HYP_BIT_PV_TIME		BIT(0)
>  #define KVM_REG_ARM_STD_HYP_BMAP_BIT_MAX	0       /* Last valid bit */
>  
> +#define KVM_REG_ARM_VENDOR_HYP_BMAP		KVM_REG_ARM_FW_BMAP_REG(2)
> +#define KVM_REG_ARM_VENDOR_HYP_BIT_PTP		BIT(0)
> +#define KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_MAX	0       /* Last valid bit */
> +
>  /* SVE registers */
>  #define KVM_REG_ARM64_SVE		(0x15 << KVM_REG_ARM_COPROC_SHIFT)
>  
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index c42426d6137e..fc3656f91aed 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -67,6 +67,7 @@ static const u64 kvm_arm_vm_scope_fw_regs[] = {
>  	KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
>  	KVM_REG_ARM_STD_BMAP,
>  	KVM_REG_ARM_STD_HYP_BMAP,
> +	KVM_REG_ARM_VENDOR_HYP_BMAP,
>  };
>  
>  /**
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index ebc0cc26cf2e..5c5098c8f1f9 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -79,6 +79,9 @@ static bool kvm_hvc_call_supported(struct kvm_vcpu *vcpu, u32 func_id)
>  	case ARM_SMCCC_HV_PV_TIME_ST:
>  		return kvm_arm_fw_reg_feat_enabled(hvc_desc->hvc_std_hyp_bmap,
>  					KVM_REG_ARM_STD_HYP_BIT_PV_TIME);
> +	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
> +		return kvm_arm_fw_reg_feat_enabled(hvc_desc->hvc_vendor_hyp_bmap,
> +					KVM_REG_ARM_VENDOR_HYP_BIT_PTP);
>  	default:
>  		/* By default, allow the services that aren't listed here */
>  		return true;
> @@ -162,7 +165,14 @@ int kvm_hvc_call_handler(struct kvm_vcpu *vcpu)
>  		break;
>  	case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
>  		val[0] = BIT(ARM_SMCCC_KVM_FUNC_FEATURES);
> -		val[0] |= BIT(ARM_SMCCC_KVM_FUNC_PTP);
> +
> +		/*
> +		 * The feature bits exposed to user-space doesn't include
> +		 * ARM_SMCCC_KVM_FUNC_FEATURES. However, we expose this to
> +		 * the guest as bit-0. Hence, left-shift the user-space
> +		 * exposed bitmap by 1 to accommodate this.
> +		 */
> +		val[0] |= hvc_desc->hvc_vendor_hyp_bmap << 1;

Having an off-by-one difference between the userspace and guest
representations of this bitmap seems like it could be a source of bugs
in the future. Its also impossible for the guest to completely hide the
vendor range if it so chooses.

Why not tie ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID and
ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID to BIT(0)? PTP would then
become BIT(1).

>  		break;
>  	case ARM_SMCCC_VENDOR_HYP_KVM_PTP_FUNC_ID:
>  		kvm_ptp_get_time(vcpu, val);
> @@ -188,6 +198,7 @@ static const u64 kvm_arm_fw_reg_ids[] = {
>  	KVM_REG_ARM_SMCCC_ARCH_WORKAROUND_2,
>  	KVM_REG_ARM_STD_BMAP,
>  	KVM_REG_ARM_STD_HYP_BMAP,
> +	KVM_REG_ARM_VENDOR_HYP_BMAP,
>  };
>  
>  void kvm_arm_init_hypercalls(struct kvm *kvm)
> @@ -196,6 +207,7 @@ void kvm_arm_init_hypercalls(struct kvm *kvm)
>  
>  	hvc_desc->hvc_std_bmap = ARM_SMCCC_STD_FEATURES;
>  	hvc_desc->hvc_std_hyp_bmap = ARM_SMCCC_STD_HYP_FEATURES;
> +	hvc_desc->hvc_vendor_hyp_bmap = ARM_SMCCC_VENDOR_HYP_FEATURES;
>  }
>  
>  int kvm_arm_get_fw_num_regs(struct kvm_vcpu *vcpu)
> @@ -285,6 +297,9 @@ int kvm_arm_get_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  	case KVM_REG_ARM_STD_HYP_BMAP:
>  		val = READ_ONCE(hvc_desc->hvc_std_hyp_bmap);
>  		break;
> +	case KVM_REG_ARM_VENDOR_HYP_BMAP:
> +		val = READ_ONCE(hvc_desc->hvc_vendor_hyp_bmap);
> +		break;
>  	default:
>  		return -ENOENT;
>  	}
> @@ -311,6 +326,10 @@ static int kvm_arm_set_fw_reg_bmap(struct kvm_vcpu *vcpu, u64 reg_id, u64 val)
>  		fw_reg_bmap = &hvc_desc->hvc_std_hyp_bmap;
>  		fw_reg_features = ARM_SMCCC_STD_HYP_FEATURES;
>  		break;
> +	case KVM_REG_ARM_VENDOR_HYP_BMAP:
> +		fw_reg_bmap = &hvc_desc->hvc_vendor_hyp_bmap;
> +		fw_reg_features = ARM_SMCCC_VENDOR_HYP_FEATURES;
> +		break;
>  	default:
>  		return -ENOENT;
>  	}
> @@ -416,6 +435,7 @@ int kvm_arm_set_fw_reg(struct kvm_vcpu *vcpu, const struct kvm_one_reg *reg)
>  		return 0;
>  	case KVM_REG_ARM_STD_BMAP:
>  	case KVM_REG_ARM_STD_HYP_BMAP:
> +	case KVM_REG_ARM_VENDOR_HYP_BMAP:
>  		return kvm_arm_set_fw_reg_bmap(vcpu, reg_id, val);
>  	default:
>  		return -ENOENT;
> diff --git a/include/kvm/arm_hypercalls.h b/include/kvm/arm_hypercalls.h
> index a1cb6e839c74..91be758ca58e 100644
> --- a/include/kvm/arm_hypercalls.h
> +++ b/include/kvm/arm_hypercalls.h
> @@ -12,6 +12,9 @@
>  #define ARM_SMCCC_STD_HYP_FEATURES \
>  	GENMASK_ULL(KVM_REG_ARM_STD_HYP_BMAP_BIT_MAX, 0)
>  
> +#define ARM_SMCCC_VENDOR_HYP_FEATURES \
> +	GENMASK_ULL(KVM_REG_ARM_VENDOR_HYP_BMAP_BIT_MAX, 0)
> +
>  int kvm_hvc_call_handler(struct kvm_vcpu *vcpu);
>  
>  static inline u32 smccc_get_function(struct kvm_vcpu *vcpu)
> -- 
> 2.35.1.473.g83b2b277ed-goog
> 

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