RE: [PATCH hyperv-next v5 01/11] arm64: kvm, smccc: Introduce and use API for detectting hypervisor presence

Michael Kelley
2025-03-10T21:16:40Z

From: Roman Kisel <romank@linux.microsoft.com> Sent: Friday, March 7, 2025 2:03 PM
>

In the Subject line,

s/detectting/detecting/

> The KVM/arm64 uses SMCCC to detect hypervisor presence. That code is
> private, and it follows the SMCCC specification. Other existing and
> emerging hypervisor guest implementations can and should use that
> standard approach as well.
>
> Factor out a common infrastructure that the guests can use, update KVM
> to employ the new API. The cenrtal notion of the SMCCC method is the

s/cenrtal/central/

> UUID of the hypervisor, and the API follows that.
>
> No functional changes. Validated with a KVM/arm64 guest.
>
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
> arch/arm64/kvm/hypercalls.c | 5 +--
> drivers/firmware/smccc/kvm_guest.c | 10 ++----
> drivers/firmware/smccc/smccc.c | 19 +++++++++++
> include/linux/arm-smccc.h | 55 +++++++++++++++++++++++++++---
> 4 files changed, 73 insertions(+), 16 deletions(-)
>
> diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
> index 27ce4cb44904..92b9bc1ea8e8 100644
> --- a/arch/arm64/kvm/hypercalls.c
> +++ b/arch/arm64/kvm/hypercalls.c
> @@ -353,10 +353,7 @@ int kvm_smccc_call_handler(struct kvm_vcpu *vcpu)
> val[0] = gpa;
> break;
> case ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID:
> - val[0] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0;
> - val[1] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1;
> - val[2] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2;
> - val[3] = ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3;
> + UUID_TO_SMCCC_RES(ARM_SMCCC_VENDOR_HYP_UID_KVM, val);
> break;
> case ARM_SMCCC_VENDOR_HYP_KVM_FEATURES_FUNC_ID:
> val[0] = smccc_feat->vendor_hyp_bmap;
> diff --git a/drivers/firmware/smccc/kvm_guest.c b/drivers/firmware/smccc/kvm_guest.c
> index f3319be20b36..b5084b309ea0 100644
> --- a/drivers/firmware/smccc/kvm_guest.c
> +++ b/drivers/firmware/smccc/kvm_guest.c
> @@ -14,17 +14,11 @@ static DECLARE_BITMAP(__kvm_arm_hyp_services,
> ARM_SMCCC_KVM_NUM_FUNCS) __ro_afte
>
> void __init kvm_init_hyp_services(void)
> {
> + uuid_t kvm_uuid = ARM_SMCCC_VENDOR_HYP_UID_KVM;
> struct arm_smccc_res res;
> u32 val[4];
>
> - if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> - return;
> -
> - arm_smccc_1_1_invoke(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> - if (res.a0 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 ||
> - res.a1 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 ||
> - res.a2 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 ||
> - res.a3 != ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3)
> + if (!arm_smccc_hyp_present(&kvm_uuid))
> return;
>
> memset(&res, 0, sizeof(res));
> diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
> index a74600d9f2d7..7399f27d58e5 100644
> --- a/drivers/firmware/smccc/smccc.c
> +++ b/drivers/firmware/smccc/smccc.c
> @@ -67,6 +67,25 @@ s32 arm_smccc_get_soc_id_revision(void)
> }
> EXPORT_SYMBOL_GPL(arm_smccc_get_soc_id_revision);
>
> +bool arm_smccc_hyp_present(const uuid_t *hyp_uuid)
> +{
> + struct arm_smccc_res res = {};
> +
> + if (arm_smccc_1_1_get_conduit() != SMCCC_CONDUIT_HVC)
> + return false;
> + arm_smccc_1_1_hvc(ARM_SMCCC_VENDOR_HYP_CALL_UID_FUNC_ID, &res);
> + if (res.a0 == SMCCC_RET_NOT_SUPPORTED)
> + return false;
> +
> + return ({
> + const uuid_t uuid = SMCCC_RES_TO_UUID(res.a0, res.a1, res.a2, res.a3);
> + const bool present = uuid_equal(&uuid, hyp_uuid);
> +
> + present;
> + });
> +}
> +EXPORT_SYMBOL_GPL(arm_smccc_hyp_present);
> +
> static int __init smccc_devices_init(void)
> {
> struct platform_device *pdev;
> diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
> index 67f6fdf2e7cd..726f18221f1c 100644
> --- a/include/linux/arm-smccc.h
> +++ b/include/linux/arm-smccc.h
> @@ -7,6 +7,11 @@
>
> #include <linux/args.h>
> #include <linux/init.h>
> +
> +#ifndef __ASSEMBLER__
> +#include <linux/uuid.h>
> +#endif
> +
> #include <uapi/linux/const.h>
>
> /*
> @@ -107,10 +112,10 @@
> ARM_SMCCC_FUNC_QUERY_CALL_UID)
>
> /* KVM UID value: 28b46fb6-2ec5-11e9-a9ca-4b564d003a74 */
> -#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0 0xb66fb428U
> -#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1 0xe911c52eU
> -#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2 0x564bcaa9U
> -#define ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3 0x743a004dU
> +#define ARM_SMCCC_VENDOR_HYP_UID_KVM UUID_INIT(\
> + 0xb66fb428, 0xc52e, 0xe911, \
> + 0xa9, 0xca, 0x4b, 0x56, \
> + 0x4d, 0x00, 0x3a, 0x74)
>
> /* KVM "vendor specific" services */
> #define ARM_SMCCC_KVM_FUNC_FEATURES 0
> @@ -333,6 +338,48 @@ s32 arm_smccc_get_soc_id_version(void);
> */
> s32 arm_smccc_get_soc_id_revision(void);
>
> +#ifndef __ASSEMBLER__
> +
> +/**
> + * arm_smccc_hyp_present(const uuid_t *hyp_uuid)
> + *
> + * Returns `true` if the hypervisor advertises its presence via SMCCC.
> + *
> + * When the function returns `false`, the caller shall not assume that
> + * there is no hypervisor running. Instead, the caller must fall back to
> + * other approaches if any are available.
> + */
> +bool arm_smccc_hyp_present(const uuid_t *hyp_uuid);
> +
> +#define SMCCC_RES_TO_UUID(r0, r1, r2, r3) \
> + UUID_INIT( \
> + cpu_to_le32(lower_32_bits(r0)), \
> + cpu_to_le32(lower_32_bits(r1)) & 0xffff, \
> + cpu_to_le32(lower_32_bits(r1)) >> 16, \
> + cpu_to_le32(lower_32_bits(r2)) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r2)) >> 8) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r2)) >> 16) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r2)) >> 24) & 0xff, \
> + cpu_to_le32(lower_32_bits(r3)) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r3)) >> 8) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r3)) >> 16) & 0xff, \
> + (cpu_to_le32(lower_32_bits(r3)) >> 24) & 0xff \
> + )
> +
> +#define UUID_TO_SMCCC_RES(uuid_init, regs) do { \
> + const uuid_t uuid = uuid_init; \
> + (regs)[0] = le32_to_cpu((u32)uuid.b[0] | (uuid.b[1] << 8) | \
> + ((uuid.b[2]) << 16) | ((uuid.b[3]) << 24));
> \
> + (regs)[1] = le32_to_cpu((u32)uuid.b[4] | (uuid.b[5] << 8) | \
> + ((uuid.b[6]) << 16) | ((uuid.b[7]) << 24));
> \
> + (regs)[2] = le32_to_cpu((u32)uuid.b[8] | (uuid.b[9] << 8) | \
> + ((uuid.b[10]) << 16) | ((uuid.b[11]) <<
> 24)); \
> + (regs)[3] = le32_to_cpu((u32)uuid.b[12] | (uuid.b[13] << 8) | \
> + ((uuid.b[14]) << 16) | ((uuid.b[15]) <<
> 24)); \
> + } while (0)
> +
> +#endif /* !__ASSEMBLER__ */
> +
> /**
> * struct arm_smccc_res - Result from SMC/HVC call
> * @a0-a3 result values from registers 0 to 3
> --
> 2.43.0
>