KVM: Export KVM-internal symbols for sub-modules only

Rework the vast majority of KVM's exports to expose symbols only to KVM
submodules, i.e. to x86's kvm-{amd,intel}.ko and PPC's kvm-{pr,hv}.ko.
With few exceptions, KVM's exported APIs are intended (and safe) for KVM-
internal usage only.

Keep kvm_get_kvm(), kvm_get_kvm_safe(), and kvm_put_kvm() as normal
exports, as they are needed by VFIO, and are generally safe for external
usage (though ideally even the get/put APIs would be KVM-internal, and
VFIO would pin a VM by grabbing a reference to its associated file).

Implement a framework in kvm_types.h in anticipation of providing a macro
to restrict KVM-specific kernel exports, i.e. to provide symbol exports
for KVM if and only if KVM is built as one or more modules.

Link: https://lore.kernel.org/r/[email protected]
Cc: Nathan Chancellor <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>

Author: sean-jc

arch/powerpc/include/asm/Kbuild

@@ -3,7 +3,6 @@ generated-y += syscall_table_32.h
 generated-y += syscall_table_64.h
 generated-y += syscall_table_spu.h
 generic-y += agp.h
-generic-y += kvm_types.h
 generic-y += mcs_spinlock.h
 generic-y += qrwlock.h
 generic-y += early_ioremap.h

arch/powerpc/include/asm/kvm_types.h

@@ -0,0 +1,15 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_PPC_KVM_TYPES_H
+#define _ASM_PPC_KVM_TYPES_H
+
+#if IS_MODULE(CONFIG_KVM_BOOK3S_64_PR) && IS_MODULE(CONFIG_KVM_BOOK3S_64_HV)
+#define KVM_SUB_MODULES kvm-pr,kvm-hv
+#elif IS_MODULE(CONFIG_KVM_BOOK3S_64_PR)
+#define KVM_SUB_MODULES kvm-pr
+#elif IS_MODULE(CONFIG_KVM_BOOK3S_64_HV)
+#define KVM_SUB_MODULES kvm-hv
+#else
+#undef KVM_SUB_MODULES
+#endif
+
+#endif

arch/x86/include/asm/kvm_types.h

@@ -2,6 +2,16 @@
 #ifndef _ASM_X86_KVM_TYPES_H
 #define _ASM_X86_KVM_TYPES_H
 
+#if IS_MODULE(CONFIG_KVM_AMD) && IS_MODULE(CONFIG_KVM_INTEL)
+#define KVM_SUB_MODULES kvm-amd,kvm-intel
+#elif IS_MODULE(CONFIG_KVM_AMD)
+#define KVM_SUB_MODULES kvm-amd
+#elif IS_MODULE(CONFIG_KVM_INTEL)
+#define KVM_SUB_MODULES kvm-intel
+#else
+#undef KVM_SUB_MODULES
+#endif
+
 #define KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE 40
 
 #endif /* _ASM_X86_KVM_TYPES_H */

include/linux/kvm_types.h

@@ -3,6 +3,23 @@
 #ifndef __KVM_TYPES_H__
 #define __KVM_TYPES_H__
 
+#include <linux/bits.h>
+#include <linux/export.h>
+#include <linux/types.h>
+#include <asm/kvm_types.h>
+
+#ifdef KVM_SUB_MODULES
+#define EXPORT_SYMBOL_FOR_KVM_INTERNAL(symbol) \
+	EXPORT_SYMBOL_FOR_MODULES(symbol, __stringify(KVM_SUB_MODULES))
+#else
+#define EXPORT_SYMBOL_FOR_KVM_INTERNAL(symbol)
+#endif
+
+#ifndef __ASSEMBLER__
+
+#include <linux/mutex.h>
+#include <linux/spinlock_types.h>
+
 struct kvm;
 struct kvm_async_pf;
 struct kvm_device_ops;
@@ -19,13 +36,6 @@ struct kvm_memslots;
 
 enum kvm_mr_change;
 
-#include <linux/bits.h>
-#include <linux/mutex.h>
-#include <linux/types.h>
-#include <linux/spinlock_types.h>
-
-#include <asm/kvm_types.h>
-
 /*
  * Address types:
  *
@@ -116,5 +126,6 @@ struct kvm_vcpu_stat_generic {
 };
 
 #define KVM_STATS_NAME_SIZE	48
+#endif /* !__ASSEMBLER__ */
 
 #endif /* __KVM_TYPES_H__ */

virt/kvm/eventfd.c

@@ -525,7 +525,7 @@ bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin)
 
 	return false;
 }
-EXPORT_SYMBOL_GPL(kvm_irq_has_notifier);
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_irq_has_notifier);
 
 void kvm_notify_acked_gsi(struct kvm *kvm, int gsi)
 {

virt/kvm/guest_memfd.c

@@ -702,7 +702,7 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 	fput(file);
 	return r;
 }
-EXPORT_SYMBOL_GPL(kvm_gmem_get_pfn);
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn);
 
 #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
 long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long npages,
@@ -785,5 +785,5 @@ long kvm_gmem_populate(struct kvm *kvm, gfn_t start_gfn, void __user *src, long
 	fput(file);
 	return ret && !i ? ret : i;
 }
-EXPORT_SYMBOL_GPL(kvm_gmem_populate);
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_populate);
 #endif