linux-kernel - [RFC PATCH] x86/bhyve: Detect FreeBSD Bhyve hypervisor

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Message-ID: <98dd43553b2d63edd3d994816f378985d1a19d72.camel@infradead.org>
Date: Mon, 11 Aug 2025 13:16:42 +0200
From: David Woodhouse <dwmw2@...radead.org>
To: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, David Woodhouse
 <dwmw@...zon.co.uk>, "Ahmed S. Darwish" <darwi@...utronix.de>,
 linux-kernel@...r.kernel.org
Cc: Konstantin Belousov <kib@....kiev.ua>, John Baldwin <jhb@...ebsd.org>
Subject: [RFC PATCH] x86/bhyve: Detect FreeBSD Bhyve hypervisor

From: David Woodhouse <dwmw@...zon.co.uk>

This detects the Bhyve hypervisor and enables 15-bit MSI support if
available.

Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
---
RFC because the CPUID_BHYVE_FEATURES leaf is submitted to FreeBSD in
https://github.com/freebsd/freebsd-src/pull/1797 and not yet merged.
And because I haven't tested this patch at all other than building it.

It's tiny so I didn't put it behind a separate CONFIG_BHYVE_GUEST.
Should I?

 arch/x86/include/asm/hypervisor.h |  2 +
 arch/x86/kernel/cpu/Makefile      |  2 +-
 arch/x86/kernel/cpu/bhyve.c       | 62 +++++++++++++++++++++++++++++++
 arch/x86/kernel/cpu/hypervisor.c  |  1 +
 4 files changed, 66 insertions(+), 1 deletion(-)
 create mode 100644 arch/x86/kernel/cpu/bhyve.c

diff --git a/arch/x86/include/asm/hypervisor.h b/arch/x86/include/asm/hypervisor.h
index e41cbf2ec41d..9ad86a7d13f6 100644
--- a/arch/x86/include/asm/hypervisor.h
+++ b/arch/x86/include/asm/hypervisor.h
@@ -30,6 +30,7 @@ enum x86_hypervisor_type {
 	X86_HYPER_KVM,
 	X86_HYPER_JAILHOUSE,
 	X86_HYPER_ACRN,
+	X86_HYPER_BHYVE,
 };
 
 #ifdef CONFIG_HYPERVISOR_GUEST
@@ -64,6 +65,7 @@ extern const struct hypervisor_x86 x86_hyper_xen_pv;
 extern const struct hypervisor_x86 x86_hyper_kvm;
 extern const struct hypervisor_x86 x86_hyper_jailhouse;
 extern const struct hypervisor_x86 x86_hyper_acrn;
+extern const struct hypervisor_x86 x86_hyper_bhyve;
 extern struct hypervisor_x86 x86_hyper_xen_hvm;
 
 extern bool nopv;
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index 1e26179ff18c..d4cb04edbacf 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -57,7 +57,7 @@ obj-$(CONFIG_X86_SGX)			+= sgx/
 
 obj-$(CONFIG_X86_LOCAL_APIC)		+= perfctr-watchdog.o
 
-obj-$(CONFIG_HYPERVISOR_GUEST)		+= vmware.o hypervisor.o mshyperv.o
+obj-$(CONFIG_HYPERVISOR_GUEST)		+= vmware.o hypervisor.o mshyperv.o bhyve.o
 obj-$(CONFIG_ACRN_GUEST)		+= acrn.o
 
 obj-$(CONFIG_DEBUG_FS)			+= debugfs.o
diff --git a/arch/x86/kernel/cpu/bhyve.c b/arch/x86/kernel/cpu/bhyve.c
new file mode 100644
index 000000000000..6d8d6ba458ef
--- /dev/null
+++ b/arch/x86/kernel/cpu/bhyve.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * FreeBSD Bhyve guest enlightenments
+ *
+ * Copyright © 2025 Amazon.com, Inc. or its affiliates.
+ *
+ * Author: David Woodhouse <dwmw2@...radead.org>
+ */
+
+#include <linux/init.h>
+#include <linux/export.h>
+#include <asm/processor.h>
+#include <asm/hypervisor.h>
+
+static uint32_t bhyve_cpuid_base;
+static uint32_t bhyve_cpuid_max;
+
+#define CPUID_BHYVE_FEATURES		1
+
+/* Features advertised in CPUID_BHYVE_FEATURES %eax */
+#define CPUID_BHYVE_FEAT_EXT_DEST_ID	(1UL << 0) /* MSI Extended Dest ID */
+
+static uint32_t __init bhyve_detect(void)
+{
+	if (boot_cpu_data.cpuid_level < 0 ||
+            !boot_cpu_has(X86_FEATURE_HYPERVISOR))
+                return 0;
+
+	bhyve_cpuid_base = cpuid_base_hypervisor("bhyve bhyve ", 0);
+	if (!bhyve_cpuid_base)
+		return 0;
+
+	bhyve_cpuid_max = cpuid_eax(bhyve_cpuid_max);
+	return bhyve_cpuid_max;
+}
+
+static uint32_t bhyve_features(void)
+{
+	if (bhyve_cpuid_max < bhyve_cpuid_base + CPUID_BHYVE_FEATURES)
+		return 0;
+
+	return cpuid_eax(bhyve_cpuid_base + CPUID_BHYVE_FEATURES);
+}
+
+static bool __init bhyve_ext_dest_id(void)
+{
+	return !!(bhyve_features() & CPUID_BHYVE_FEAT_EXT_DEST_ID);
+}
+
+static bool __init bhyve_x2apic_available(void)
+{
+	/* Bhyve has always supported x2apic */
+	return true;
+}
+
+const struct hypervisor_x86 x86_hyper_bhyve __refconst = {
+	.name			= "Bhyve",
+	.detect			= bhyve_detect,
+	.init.init_platform	= x86_init_noop,
+	.init.x2apic_available	= bhyve_x2apic_available,
+	.init.msi_ext_dest_id	= bhyve_ext_dest_id,
+};
diff --git a/arch/x86/kernel/cpu/hypervisor.c b/arch/x86/kernel/cpu/hypervisor.c
index 553bfbfc3a1b..157cf9edeb35 100644
--- a/arch/x86/kernel/cpu/hypervisor.c
+++ b/arch/x86/kernel/cpu/hypervisor.c
@@ -36,6 +36,7 @@ static const __initconst struct hypervisor_x86 * const hypervisors[] =
 #endif
 	&x86_hyper_vmware,
 	&x86_hyper_ms_hyperv,
+	&x86_hyper_bhyve,
 #ifdef CONFIG_KVM_GUEST
 	&x86_hyper_kvm,
 #endif
-- 
2.49.0



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