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Message-ID: <14a199d8-1cf3-49bc-8e0d-92d9c8407b4f@linux.microsoft.com>
Date: Mon, 24 Feb 2025 15:22:19 -0800
From: Roman Kisel <romank@...ux.microsoft.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: benhill@...rosoft.com, bperkins@...rosoft.com, sunilmut@...rosoft.com,
bhelgaas@...gle.com, Borislav Petkov <bp@...en8.de>,
Catalin Marinas <catalin.marinas@....com>, Conor Dooley
<conor+dt@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>,
Dexuan Cui <decui@...rosoft.com>, Haiyang Zhang <haiyangz@...rosoft.com>,
"H. Peter Anvin" <hpa@...or.com>, krzk+dt@...nel.org,
Krzysztof Wilczyński <kw@...ux.com>,
"K. Y. Srinivasan" <kys@...rosoft.com>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
Ingo Molnar <mingo@...hat.com>, Rob Herring <robh@...nel.org>,
ssengar@...ux.microsoft.com, Thomas Gleixner <tglx@...utronix.de>,
Wei Liu <wei.liu@...nel.org>, Will Deacon <will@...nel.org>,
devicetree@...r.kernel.org, Linux-Arch <linux-arch@...r.kernel.org>,
linux-arm-kernel@...ts.infradead.org, linux-hyperv@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH hyperv-next v4 1/6] arm64: hyperv: Use SMCCC to detect
hypervisor presence
Hi Arnd,
[...]
>> I would suggest moving the UUID values into a variable next
>> to the caller like
>>
>> #define ARM_SMCCC_VENDOR_HYP_UID_KVM \
>> UUID_INIT(0x28b46fb6, 0x2ec5, 0x11e9, 0xa9, 0xca, 0x4b, 0x56,
>> 0x4d, 0x00, 0x3a, 0x74)
>>
>> and then just pass that into arm_smccc_hyp_present(). (please
>> double-check the endianess of the definition here, I probably
>> got it wrong myself).
I worked out a variation [1] of the change that you said looked good.
Here, there is a helper macro for creating uuid_t's when checking
for the hypervisor running via SMCCC to avoid using the bare UUID_INIT.
Valiadted with KVM/arm64 and Hyper-V/arm64. Do you think this is a
better approach than converting by hand?
If that looks too heavy, maybe could leave out converting the expected
register values to UUID, and pass the expected register values to
arm_smccc_hyp_present directly. That way, instead of
bool arm_smccc_hyp_present(const uuid_t *hyp_uuid);
we'd have
bool arm_smccc_hyp_present(u32 reg0, u32 reg1, u32 reg2, u32 reg2);
Please let me know what you think!
[1]
---
arch/arm64/hyperv/mshyperv.c | 16 +++++---------
drivers/firmware/smccc/kvm_guest.c | 13 +++++------
drivers/firmware/smccc/smccc.c | 19 ++++++++++++++++
include/linux/arm-smccc.h | 35 ++++++++++++++++++++++++++++++
4 files changed, 64 insertions(+), 19 deletions(-)
diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
index 16e721d8e5df..b8468bd65ec0 100644
--- a/arch/arm64/hyperv/mshyperv.c
+++ b/arch/arm64/hyperv/mshyperv.c
@@ -43,18 +43,12 @@ static bool hyperv_detect_via_acpi(void)
static bool hyperv_detect_via_smccc(void)
{
- struct arm_smccc_res res = {};
+ uuid_t hyperv_uuid = HYP_UUID_INIT(ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_0,
+ ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_1,
+ ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_2,
+ ARM_SMCCC_VENDOR_HYP_UID_HYPERV_REG_3);
- 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;
+ return arm_smccc_hyp_present(&hyperv_uuid);
}
static int __init hyperv_init(void)
diff --git a/drivers/firmware/smccc/kvm_guest.c
b/drivers/firmware/smccc/kvm_guest.c
index f3319be20b36..48c3622b2aa6 100644
--- a/drivers/firmware/smccc/kvm_guest.c
+++ b/drivers/firmware/smccc/kvm_guest.c
@@ -14,17 +14,14 @@ 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 = HYP_UUID_INIT(ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_0,
+ ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_1,
+ ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_2,
+ ARM_SMCCC_VENDOR_HYP_UID_KVM_REG_3);
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..0943abb3f4c9 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 = HYP_UUID_INIT(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..60be36254364 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 +338,36 @@ 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 HYP_UUID_INIT(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 \
+ )
+
+#endif /* !__ASSEMBLER__ */
+
/**
* struct arm_smccc_res - Result from SMC/HVC call
* @a0-a3 result values from registers 0 to 3
--
Thank you,
Roman
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