linux-kernel - [PATCH v2 2/2] x86: make Hyper-V support optional

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Message-Id: <20201202211949.17730-2-info@metux.net>
Date:   Wed,  2 Dec 2020 22:19:49 +0100
From:   "Enrico Weigelt, metux IT consult" <info@...ux.net>
To:     linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, dmitry.torokhov@...il.com, derek.kiernan@...inx.com,
        dragan.cvetic@...inx.com, richardcochran@...il.com,
        linux-hyperv@...r.kernel.org, linux-input@...r.kernel.org,
        netdev@...r.kernel.org
Subject: [PATCH v2 2/2] x86: make Hyper-V support optional

Make it possible to opt-out from Hyper-V support, for minimized kernels
that never will by run under Hyper-V. (eg. high-density virtualization
or embedded systems)

Average distro kernel will leave it on, therefore default to y.

Signed-off-by: Enrico Weigelt <info@...ux.net>
---
 arch/x86/Kconfig                 | 11 +++++++++++
 arch/x86/kernel/cpu/Makefile     |  4 ++--
 arch/x86/kernel/cpu/hypervisor.c |  2 ++
 drivers/hv/Kconfig               |  2 +-
 4 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index eff12460cb3c..57d20591d6ee 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -812,6 +812,17 @@ config VMWARE_GUEST
 	  density virtualization or embedded systems running (para)virtualized
 	  workloads.
 
+config HYPERV_GUEST
+	bool "Hyper-V Guest support"
+	default y
+	help
+	  This option enables several optimizations for running under the
+	  Hyper-V hypervisor.
+
+	  Disabling it saves a few kb, for stripped down kernels eg. in high
+	  density virtualization or embedded systems running (para)virtualized
+	  workloads.
+
 config KVM_GUEST
 	bool "KVM Guest support (including kvmclock)"
 	depends on PARAVIRT
diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile
index a615b0152bf0..5536b801cb44 100644
--- a/arch/x86/kernel/cpu/Makefile
+++ b/arch/x86/kernel/cpu/Makefile
@@ -51,9 +51,9 @@ obj-$(CONFIG_X86_CPU_RESCTRL)		+= resctrl/
 
 obj-$(CONFIG_X86_LOCAL_APIC)		+= perfctr-watchdog.o
 
-obj-$(CONFIG_HYPERVISOR_GUEST)		+= hypervisor.o mshyperv.o
+obj-$(CONFIG_HYPERVISOR_GUEST)		+= hypervisor.o
 obj-$(CONFIG_VMWARE_GUEST)		+= vmware.o
-
+obj-$(CONFIG_HYPERV_GUEST)		+= mshyperv.o
 obj-$(CONFIG_ACRN_GUEST)		+= acrn.o
 
 ifdef CONFIG_X86_FEATURE_NAMES
diff --git a/arch/x86/kernel/cpu/hypervisor.c b/arch/x86/kernel/cpu/hypervisor.c
index c0e770a224aa..32d6b2084d05 100644
--- a/arch/x86/kernel/cpu/hypervisor.c
+++ b/arch/x86/kernel/cpu/hypervisor.c
@@ -37,7 +37,9 @@ static const __initconst struct hypervisor_x86 * const hypervisors[] =
 #ifdef CONFIG_VMWARE_GUEST
 	&x86_hyper_vmware,
 #endif
+#ifdef CONFIG_HYPERV_GUEST
 	&x86_hyper_ms_hyperv,
+#endif
 #ifdef CONFIG_KVM_GUEST
 	&x86_hyper_kvm,
 #endif
diff --git a/drivers/hv/Kconfig b/drivers/hv/Kconfig
index 79e5356a737a..7b3094c59a81 100644
--- a/drivers/hv/Kconfig
+++ b/drivers/hv/Kconfig
@@ -4,7 +4,7 @@ menu "Microsoft Hyper-V guest support"
 
 config HYPERV
 	tristate "Microsoft Hyper-V client drivers"
-	depends on X86 && ACPI && X86_LOCAL_APIC && HYPERVISOR_GUEST
+	depends on X86 && ACPI && X86_LOCAL_APIC && HYPERV_GUEST
 	select PARAVIRT
 	select X86_HV_CALLBACK_VECTOR
 	help
-- 
2.11.0