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Message-ID: <593c22ca-6544-423d-84ee-7a06c6b8b5b9@linux.microsoft.com>
Date: Thu, 13 Feb 2025 15:23:56 -0800
From: Roman Kisel <romank@...ux.microsoft.com>
To: Arnd Bergmann <arnd@...db.de>, 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
Cc: benhill@...rosoft.com, bperkins@...rosoft.com, sunilmut@...rosoft.com
Subject: Re: [PATCH hyperv-next v4 1/6] arm64: hyperv: Use SMCCC to detect
hypervisor presence
On 2/11/2025 10:54 PM, Arnd Bergmann wrote:
> On Wed, Feb 12, 2025, at 02:43, Roman Kisel wrote:
>> +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 <romank@...ux.microsoft.com>
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
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