KVM: Move x86's version of struct kvm_mmu_memory_cache to common code

Move x86's 'struct kvm_mmu_memory_cache' to common code in anticipation
of moving the entire x86 implementation code to common KVM and reusing
it for arm64 and MIPS. Add a new architecture specific asm/kvm_types.h
to control the existence and parameters of the struct. The new header
is needed to avoid a chicken-and-egg problem with asm/kvm_host.h as all
architectures define instances of the struct in their vCPU structs.

Add an asm-generic version of kvm_types.h to avoid having empty files on
PPC and s390 in the long term, and for arm64 and mips in the short term.

Suggested-by: Christoffer Dall <[e-mail]>
Reviewed-by: Ben Gardon <[e-mail]>
Signed-off-by: Sean Christopherson <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>

arch/arm64/include/asm/Kbuild

···
 # SPDX-License-Identifier: GPL-2.0
 generic-y += early_ioremap.h
+generic-y += kvm_types.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += qrwlock.h

arch/mips/include/asm/Kbuild

···
 generated-y += syscall_table_64_n64.h
 generated-y += syscall_table_64_o32.h
 generic-y += export.h
+generic-y += kvm_types.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += parport.h

arch/powerpc/include/asm/Kbuild

···
 generated-y += syscall_table_c32.h
 generated-y += syscall_table_spu.h
 generic-y += export.h
+generic-y += kvm_types.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h
 generic-y += vtime.h

arch/s390/include/asm/Kbuild

···
 
 generic-y += asm-offsets.h
 generic-y += export.h
+generic-y += kvm_types.h
 generic-y += local64.h
 generic-y += mcs_spinlock.h

arch/x86/include/asm/kvm_host.h

···
 enum x86_intercept;
 enum x86_intercept_stage;
 
-#define KVM_NR_MEM_OBJS 40
-
 #define KVM_NR_DB_REGS	4
 
 #define DR6_BD		(1 << 13)
···
 #define KVM_APIC_PV_EOI_PENDING	1
 
 struct kvm_kernel_irq_routing_entry;
-
-/*
- * We don't want allocation failures within the mmu code, so we preallocate
- * enough memory for a single page fault in a cache.
- */
-struct kvm_mmu_memory_cache {
-	int nobjs;
-	gfp_t gfp_zero;
-	struct kmem_cache *kmem_cache;
-	void *objects[KVM_NR_MEM_OBJS];
-};
 
 /*
  * the pages used as guest page table on soft mmu are tracked by

arch/x86/include/asm/kvm_types.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_KVM_TYPES_H
+#define _ASM_X86_KVM_TYPES_H
+
+#define KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE 40
+
+#endif /* _ASM_X86_KVM_TYPES_H */

include/asm-generic/kvm_types.h

···
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_GENERIC_KVM_TYPES_H
+#define _ASM_GENERIC_KVM_TYPES_H
+
+#endif

include/linux/kvm_types.h

···
 
 #include <linux/types.h>
 
+#include <asm/kvm_types.h>
+
 /*
  * Address types:
  *
···
 	kvm_pfn_t pfn;
 	bool dirty;
 };
+
+#ifdef KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE
+/*
+ * Memory caches are used to preallocate memory ahead of various MMU flows,
+ * e.g. page fault handlers.  Gracefully handling allocation failures deep in
+ * MMU flows is problematic, as is triggering reclaim, I/O, etc... while
+ * holding MMU locks.  Note, these caches act more like prefetch buffers than
+ * classical caches, i.e. objects are not returned to the cache on being freed.
+ */
+struct kvm_mmu_memory_cache {
+	int nobjs;
+	gfp_t gfp_zero;
+	struct kmem_cache *kmem_cache;
+	void *objects[KVM_ARCH_NR_OBJS_PER_MEMORY_CACHE];
+};
+#endif
+
 
 #endif /* __KVM_TYPES_H__ */