[PATCH v3 04/12] KVM: x86: Add CONFIG_KVM_VMWARE

[Zack Rusin <zack.rusin@broadcom.com>]

Add CONFIG_KVM_VMWARE, defaulting to "y", to control whether KVM's
VMware emulation is built.  When it is disabled, vmware.o isn't built,
the VMware predicates are compile-time false, and the
enable_vmware_backdoor module parameter doesn't exist: a
kvm.enable_vmware_backdoor setting is ignored, and modprobe warns about
an unknown parameter.

VMware emulation is only useful to VMware-aware guests and to VMMs that
offer VMware compatibility.  Let kernels that don't need it, e.g. to
reduce the attack surface exposed to guests, leave it out, as they can
already do for Hyper-V and Xen emulation.  Default to "y" so that
existing configurations keep the backdoor and its module parameter.

Provide __always_inline stubs for the predicates that gate VMware
behavior, so that callers need no #ifdefs and the compiler drops the
dead branches.  Leave the operations behind the predicates declared but
undefined when the option is disabled: a call that isn't guarded by a
predicate then fails to link instead of silently doing nothing.

Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/Zy0__5YB9F5d0eZn@google.com
Link: https://lore.kernel.org/r/e3f943a7-a40a-45cb-b0d9-e3ed58344d8b@redhat.com
Link: https://lore.kernel.org/r/aIEmawm9gLflg8zt@google.com
Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
---
 arch/x86/kvm/Kconfig  | 12 ++++++++++++
 arch/x86/kvm/Makefile |  4 ++--
 arch/x86/kvm/vmware.h | 31 +++++++++++++++++++++++++++++++
 3 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 1719059570fb..b34d6d0e30c9 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -212,6 +212,18 @@ config KVM_HYPERV
 
 	  If unsure, say "Y".
 
+config KVM_VMWARE
+	bool "VMware guest support"
+	depends on KVM_X86
+	default y
+	help
+	  Provides KVM support for emulating VMware interfaces. VMware-aware
+	  guests use these interfaces to communicate with the hypervisor.
+	  Userspace hypervisors can also use them to provide VMware
+	  compatibility to their guests.
+
+	  If unsure, say "Y".
+
 config KVM_XEN
 	bool "Support for Xen hypercall interface"
 	depends on KVM_X86
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index 0cb47cfc1162..794c847ccecc 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -6,13 +6,13 @@ ccflags-$(CONFIG_KVM_WERROR) += -Werror
 include $(srctree)/virt/kvm/Makefile.kvm
 
 kvm-y			+= x86.o emulate.o irq.o lapic.o cpuid.o msrs.o pmu.o regs.o \
-			   mtrr.o debugfs.o mmu/mmu.o mmu/page_track.o mmu/spte.o \
-			   vmware.o
+			   mtrr.o debugfs.o mmu/mmu.o mmu/page_track.o mmu/spte.o
 
 kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
 kvm-$(CONFIG_KVM_IOAPIC) += i8259.o i8254.o ioapic.o
 kvm-$(CONFIG_KVM_HYPERV) += hyperv.o
 kvm-$(CONFIG_KVM_XEN)	+= xen.o
+kvm-$(CONFIG_KVM_VMWARE) += vmware.o
 kvm-$(CONFIG_KVM_SMM)	+= smm.o
 
 kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
diff --git a/arch/x86/kvm/vmware.h b/arch/x86/kvm/vmware.h
index bf250cc6e232..5951e419e1a7 100644
--- a/arch/x86/kvm/vmware.h
+++ b/arch/x86/kvm/vmware.h
@@ -4,10 +4,41 @@
 
 #include <linux/kvm_host.h>
 
+#ifdef CONFIG_KVM_VMWARE
+
 bool kvm_is_vmware_backdoor_enabled(struct kvm_vcpu *vcpu);
 bool kvm_is_vmware_io_port(struct kvm_vcpu *vcpu, u16 port);
 bool kvm_is_vmware_backdoor_pmc(struct kvm_vcpu *vcpu, u32 pmc_idx);
 bool kvm_is_vmware_backdoor_opcode(u8 opcode_len, u8 opcode);
+
+#else /* !CONFIG_KVM_VMWARE */
+
+static __always_inline bool
+kvm_is_vmware_backdoor_enabled(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
+
+static __always_inline bool
+kvm_is_vmware_io_port(struct kvm_vcpu *vcpu, u16 port)
+{
+	return false;
+}
+
+static __always_inline bool
+kvm_is_vmware_backdoor_pmc(struct kvm_vcpu *vcpu, u32 pmc_idx)
+{
+	return false;
+}
+
+static __always_inline bool
+kvm_is_vmware_backdoor_opcode(u8 opcode_len, u8 opcode)
+{
+	return false;
+}
+
+#endif /* CONFIG_KVM_VMWARE */
+
 int kvm_vmware_pmu_rdpmc(struct kvm_vcpu *vcpu, unsigned int idx, u64 *data);
 
 #endif /* __KVM_X86_VMWARE_H */
-- 
2.53.0