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

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Message-ID: <76fab40c181f671e5505e29c7ca920f4eee4dd5d.camel@infradead.org>
Date: Wed, 13 Aug 2025 23:07:22 +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>, "Ahmed S. Darwish"
 <darwi@...utronix.de>,  linux-kernel@...r.kernel.org
Cc: Konstantin Belousov <kib@....kiev.ua>, John Baldwin <jhb@...ebsd.org>, 
 Colin Percival <cperciva@...snap.com>
Subject: Re: [RFC PATCH] x86/bhyve: Detect FreeBSD Bhyve hypervisor

On Mon, 2025-08-11 at 13:16 +0200, David Woodhouse wrote:
> 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.

Now merged and should be in FreeBSD 15.0 release. Thanks, Colin!
https://github.com/freebsd/freebsd-src/commit/4322d597453d6

> 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


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