KVM: x86: allow compiling out the Xen hypercall interface

The Xen hypercall interface adds to the attack surface of the hypervisor
and will be used quite rarely.  Allow compiling it out.

Suggested-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 7ac5926..a788d51 100644 (file)
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -103,6 +103,15 @@ config KVM_AMD_SEV
          Provides support for launching Encrypted VMs (SEV) and Encrypted VMs
          with Encrypted State (SEV-ES) on AMD processors.
 
+config KVM_XEN
+       bool "Support for Xen hypercall interface"
+       depends on KVM
+       help
+         Provides KVM support for the hosting Xen HVM guests and
+         passing Xen hypercalls to userspace.
+
+         If in doubt, say "N".
+
 config KVM_MMU_AUDIT
        bool "Audit KVM MMU"
        depends on KVM && TRACEPOINTS

diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index aeab168..1b4766f 100644 (file)
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -14,11 +14,12 @@ kvm-y                       += $(KVM)/kvm_main.o $(KVM)/coalesced_mmio.o \
                                $(KVM)/dirty_ring.o
 kvm-$(CONFIG_KVM_ASYNC_PF)     += $(KVM)/async_pf.o
 
-kvm-y                  += x86.o emulate.o i8259.o irq.o lapic.o xen.o \
+kvm-y                  += x86.o emulate.o i8259.o irq.o lapic.o \
                           i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
                           hyperv.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_XEN)  += xen.o
 
 kvm-intel-y            += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
                           vmx/evmcs.o vmx/nested.o vmx/posted_intr.o

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bfc9284..4a5ce57 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3755,11 +3755,13 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
        case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
                r = 1;
                break;
+#ifdef CONFIG_KVM_XEN
        case KVM_CAP_XEN_HVM:
                r = KVM_XEN_HVM_CONFIG_HYPERCALL_MSR |
                    KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
                    KVM_XEN_HVM_CONFIG_SHARED_INFO;
                break;
+#endif
        case KVM_CAP_SYNC_REGS:
                r = KVM_SYNC_X86_VALID_FIELDS;
                break;
@@ -5012,6 +5014,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
        case KVM_GET_SUPPORTED_HV_CPUID:
                r = kvm_ioctl_get_supported_hv_cpuid(vcpu, argp);
                break;
+#ifdef CONFIG_KVM_XEN
        case KVM_XEN_VCPU_GET_ATTR: {
                struct kvm_xen_vcpu_attr xva;
 
@@ -5032,6 +5035,7 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
                r = kvm_xen_vcpu_set_attr(vcpu, &xva);
                break;
        }
+#endif
        default:
                r = -EINVAL;
        }
@@ -5653,6 +5657,7 @@ set_pit2_out:
                        kvm->arch.bsp_vcpu_id = arg;
                mutex_unlock(&kvm->lock);
                break;
+#ifdef CONFIG_KVM_XEN
        case KVM_XEN_HVM_CONFIG: {
                struct kvm_xen_hvm_config xhc;
                r = -EFAULT;
@@ -5681,6 +5686,7 @@ set_pit2_out:
                r = kvm_xen_hvm_set_attr(kvm, &xha);
                break;
        }
+#endif
        case KVM_SET_CLOCK: {
                struct kvm_clock_data user_ns;
                u64 now_ns;
@@ -8039,8 +8045,10 @@ void kvm_arch_exit(void)
        kvm_mmu_module_exit();
        free_percpu(user_return_msrs);
        kmem_cache_destroy(x86_fpu_cache);
+#ifdef CONFIG_KVM_XEN
        static_key_deferred_flush(&kvm_xen_enabled);
        WARN_ON(static_branch_unlikely(&kvm_xen_enabled.key));
+#endif
 }
 
 static int __kvm_vcpu_halt(struct kvm_vcpu *vcpu, int state, int reason)

diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index b66a921..87eaf2b 100644 (file)
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -9,6 +9,7 @@
 #ifndef __ARCH_X86_KVM_XEN_H__
 #define __ARCH_X86_KVM_XEN_H__
 
+#ifdef CONFIG_KVM_XEN
 #include <linux/jump_label_ratelimit.h>
 
 extern struct static_key_false_deferred kvm_xen_enabled;
@@ -18,7 +19,6 @@ int kvm_xen_vcpu_set_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data)
 int kvm_xen_vcpu_get_attr(struct kvm_vcpu *vcpu, struct kvm_xen_vcpu_attr *data);
 int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
 int kvm_xen_hvm_get_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data);
-int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
 int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data);
 int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc);
 void kvm_xen_destroy_vm(struct kvm *kvm);
@@ -38,6 +38,28 @@ static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
 
        return 0;
 }
+#else
+static inline int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
+{
+       return 1;
+}
+
+static inline void kvm_xen_destroy_vm(struct kvm *kvm)
+{
+}
+
+static inline bool kvm_xen_hypercall_enabled(struct kvm *kvm)
+{
+       return false;
+}
+
+static inline int kvm_xen_has_interrupt(struct kvm_vcpu *vcpu)
+{
+       return 0;
+}
+#endif
+
+int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
 
 /* 32-bit compatibility definitions, also used natively in 32-bit build */
 #include <asm/pvclock-abi.h>