Re: [PATCH hyperv-next v4 1/6] arm64: hyperv: Use SMCCC to detect hypervisor presence
From: Roman Kisel <hidden>
Date: 2025-02-13 23:23:57
Also in:
linux-arch, linux-devicetree, linux-hyperv, linux-pci, lkml
Subsystem:
arm64 port (aarch64 architecture), secure monitor call(smc) calling convention (smccc), the rest · Maintainers:
Catalin Marinas, Will Deacon, Mark Rutland, Lorenzo Pieralisi, Sudeep Holla, Linus Torvalds
On 2/11/2025 10:54 PM, Arnd Bergmann wrote:
On Wed, Feb 12, 2025, at 02:43, Roman Kisel wrote:quoted
+static bool hyperv_detect_via_smccc(void) +{ + 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 res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 && + res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 && + res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 && + res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3; +}I had to double-check that this function is safe to call on other hypervisors, at least when they follow the smccc spec. Seeing that we have the same helper function checking for ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_* and there was another patch set adding a copy for gunyah, I wonder if we can put this into a drivers/firmware/smccc/smccc.c directly the same way we handle soc_id, and make it return a uuid_t, or perhaps take a constant uuid_t to compare against.
That would be very neat! I implemented the idea [1], please let me know what you think. I can use that in the next version of the patch series if looks good. There is a function and a macro to make calling the function easier. As the SMCCC header is used by the assembler, too, hence I had to add __ASSEBLER__ guardrails. Another option could be to pass four u32's not to use uuid_t so the header stays a healthy food for the assembler :) For Gunyah, that would be ARM_SMCCC_HYP_PRESENT(GUNYAH) when using the change below. From f0d645e900c24f5be045b0f831f1e11494967b7f Mon Sep 17 00:00:00 2001 From: Roman Kisel <redacted> Date: Thu, 13 Feb 2025 15:10:45 -0800 Subject: [PATCH] drivers, smcc: Introduce arm_smccc_hyp_present --- arch/arm64/hyperv/mshyperv.c | 18 +---------------- drivers/firmware/smccc/kvm_guest.c | 9 +-------- drivers/firmware/smccc/smccc.c | 24 ++++++++++++++++++++++ include/linux/arm-smccc.h | 32 ++++++++++++++++++++++++++++++ 4 files changed, 58 insertions(+), 25 deletions(-)
diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 16e721d8e5df..0c5babe9e1ff 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c@@ -41,22 +41,6 @@ static bool hyperv_detect_via_acpi(void) #endif } -static bool hyperv_detect_via_smccc(void) -{ - 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 res.a0 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0 && - res.a1 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1 && - res.a2 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2 && - res.a3 == ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3; -} - static int __init hyperv_init(void) { struct hv_get_vp_registers_output result;
@@ -69,7 +53,7 @@ static int __init hyperv_init(void) * * In such cases, do nothing and return success. */ - if (!hyperv_detect_via_acpi() && !hyperv_detect_via_smccc()) + if (!hyperv_detect_via_acpi() && !ARM_SMCCC_HYP_PRESENT(HYPERV)) return 0; /* Setup the guest ID */
diff --git a/drivers/firmware/smccc/kvm_guest.c b/drivers/firmware/smccc/kvm_guest.c index f3319be20b36..ae37476cabc1 100644
--- a/drivers/firmware/smccc/kvm_guest.c
+++ b/drivers/firmware/smccc/kvm_guest.c@@ -17,14 +17,7 @@ void __init kvm_init_hyp_services(void) 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)) return; memset(&res, 0, sizeof(res));
diff --git a/drivers/firmware/smccc/smccc.c b/drivers/firmware/smccc/smccc.c
index a74600d9f2d7..86f75f44895f 100644
--- a/drivers/firmware/smccc/smccc.c
+++ b/drivers/firmware/smccc/smccc.c@@ -67,6 +67,30 @@ 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 = {}; + struct { + u32 dwords[4] + } __packed res_uuid; + + BUILD_BUG_ON(sizeof(res_uuid) != sizeof(uuid_t)); + + 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; + + res_uuid.dwords[0] = res.a0; + res_uuid.dwords[1] = res.a1; + res_uuid.dwords[2] = res.a2; + res_uuid.dwords[3] = res.a3; + + return uuid_equal((uuid_t *)&res_uuid, hyp_uuid); +} +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..63925506a0e5 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> /*
@@ -333,6 +338,33 @@ 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 ARM_SMCCC_HYP_PRESENT(HYP) \ + ({ \ + const u32 uuid_as_dwords[4] = { \ + ARM_SMCCC_VENDOR_HYP_UID_ ## HYP ## _REG_0, \ + ARM_SMCCC_VENDOR_HYP_UID_ ## HYP ## _REG_1, \ + ARM_SMCCC_VENDOR_HYP_UID_ ## HYP ## _REG_2, \ + ARM_SMCCC_VENDOR_HYP_UID_ ## HYP ## _REG_3 \ + }; \ + \ + arm_smccc_hyp_present((const uuid_t *)uuid_as_dwords); \ + }) \ + +#endif /* !__ASSEMBLER__ */ + /** * struct arm_smccc_res - Result from SMC/HVC call * @a0-a3 result values from registers 0 to 3
--
2.43.0
>
> Arnd
--
Thank you,
Roman