Re: [PATCH 26/26] KVM: Hide KVM internal data structures and values from kernel at-large

[Anup Patel]

On Sat, Sep 16, 2023 at 6:02 AM Sean Christopherson <seanjc@xxxxxxxxxx> wrote:
>
> Wrap all KVM internal APIs, data structures, values, etc. in public
> headers with "#ifdef __KVM__" to effectively hide KVM's internal details
> from other subsystems and the kernel at-large.  Hiding KVM details for
> all architectures will, in the very distant future, allow loading a new
> (or old) KVM module without needing to rebuild and reboot the entire
> kernel, or to even allow loading and running multiple versions of KVM
> simultaneously on a single host.
>
> To allow different instances of KVM modules to freely modify KVM data
> structures, enums, #defines, etc., e.g. the struct kvm_vcpu layout, there
> must be exactly zero dereferences of KVM-defined structures/values in
> non-KVM code (excepting code for architectures that don't support such
> shenanigans).  Any such references could lead to latent bugs, e.g. as the
> kernel would think a KVM structure has layout X, but in reality the
> current incarnation of KVM uses layout Y.
>
> In KVM x86, all remaining non-KVM references to KVM details have been now
> eliminated.  To harden KVM against new references being introduced, hide
> KVM's details to ensure that KVM doesn’t create a de facto ABI with the
> rest of the kernel.
>
> Use #ifdeffery to hide KVM details as doing so requires, by far, the least
> amount of churn and impact on architectures that freely share select KVM
> details with the rest of the kernel, e.g. s390, ARM64 and PPC, have
> significant usage of KVM-defined APIs, structures, values, etc.  E.g.
> attempting to extract the "private" chunks into dedicated KVM-internal
> headers would require massive churn, even on x86, and it's not obvious the
> end result would be a net positive (all attempts at moving code around
> failed long before getting anywhere near compiling cleanly).
>
> Another (bad) alternative that would be relative churn-free would be to
> move the KVM headers to a dedicated KVM-specific path while maintaining
> the generic layout, e.g. something like virt/kvm/include/linux.  That
> would allow x86 to simply omit the KVM-specific include path.  But that
> would require modifying the global include path, i.e. would make KVM a
> really special snowflake and set the awful precedent that it's "ok" to
> add subsystem specific directories to the global include path.
>
> Grant exceptions to asm-offsets.c as needed, and to s390's VFIO AP driver.
> Creating a KVM-specific asm-offsets, as was done for x86, adds no value
> (x86 did so to avoid exposing vendor specific headers) and doesn't create
> much of a "slippery slope" risk.  s390's VFIO AP driver on the other hand
> is simply too intertwined with KVM to realistically treat it as anything
> other than KVM code, despite it living in crypto drivers, e.g. the driver
> has some rather crazy lock ordering rules between the device and KVM.
>
> Add a static assert that __KVM__ is defined in trace/events/kvm.h, as that
> is effectively a private KVM header that just happens to live in a public
> path.
>
> Shuffle a few PPC includes and an s390 declaration as needed, and
> opportunistically include kvm_host.h in trace/events.kvm.h instead of
> relying on the parent to provide the right includes.
>
> Cc: Anish Ghulati <aghulati@xxxxxxxxxx>
> Cc: Venkatesh Srinivas <venkateshs@xxxxxxxxxxxx>
> Cc: Andrew Thornton <andrewth@xxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

For KVM RISC-V:
Anup Patel <anup@xxxxxxxxxxxxxx>

Regards,
Anup

> ---
>  arch/arm64/include/asm/kvm_emulate.h     | 3 +++
>  arch/arm64/include/asm/kvm_host.h        | 2 ++
>  arch/arm64/include/asm/kvm_mmu.h         | 4 ++++
>  arch/arm64/kernel/asm-offsets.c          | 2 ++
>  arch/arm64/kvm/hyp/Makefile              | 2 +-
>  arch/arm64/kvm/hyp/nvhe/Makefile         | 3 ++-
>  arch/arm64/kvm/hyp/vhe/Makefile          | 2 +-
>  arch/mips/include/asm/kvm_host.h         | 2 ++
>  arch/mips/kernel/asm-offsets.c           | 2 ++
>  arch/powerpc/include/asm/kvm_book3s.h    | 3 +++
>  arch/powerpc/include/asm/kvm_book3s_64.h | 2 ++
>  arch/powerpc/include/asm/kvm_booke.h     | 4 ++++
>  arch/powerpc/include/asm/kvm_host.h      | 7 ++++---
>  arch/powerpc/include/asm/kvm_ppc.h       | 2 ++
>  arch/powerpc/kernel/asm-offsets.c        | 1 +
>  arch/riscv/include/asm/kvm_host.h        | 3 +++
>  arch/riscv/kernel/asm-offsets.c          | 1 +
>  arch/s390/include/asm/kvm_host.h         | 7 +++++--
>  arch/s390/kernel/asm-offsets.c           | 1 +
>  arch/x86/include/asm/kvm_host.h          | 3 +++
>  drivers/s390/crypto/vfio_ap_drv.c        | 1 +
>  drivers/s390/crypto/vfio_ap_ops.c        | 2 ++
>  include/linux/kvm_host.h                 | 4 ++++
>  include/linux/kvm_types.h                | 3 +++
>  include/trace/events/kvm.h               | 5 +++++
>  virt/kvm/Makefile.kvm                    | 2 +-
>  26 files changed, 64 insertions(+), 9 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 3d6725ff0bf6..5861fa00763b 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -21,6 +21,8 @@
>  #include <asm/cputype.h>
>  #include <asm/virt.h>
>
> +#ifdef __KVM__
> +
>  #define CURRENT_EL_SP_EL0_VECTOR       0x0
>  #define CURRENT_EL_SP_ELx_VECTOR       0x200
>  #define LOWER_EL_AArch64_VECTOR                0x400
> @@ -615,4 +617,5 @@ static __always_inline void kvm_reset_cptr_el2(struct kvm_vcpu *vcpu)
>
>         kvm_write_cptr_el2(val);
>  }
> +#endif /* __KVM__ */
>  #endif /* __ARM64_KVM_EMULATE_H__ */
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 89b40c34f0af..ba4065db5d5c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -93,6 +93,7 @@ static inline bool kvm_pmu_counter_deferred(struct perf_event_attr *attr)
>         return (!has_vhe() && attr->exclude_host);
>  }
>
> +#ifdef __KVM__
>  DECLARE_STATIC_KEY_FALSE(userspace_irqchip_in_use);
>
>  extern unsigned int __ro_after_init kvm_sve_max_vl;
> @@ -1149,4 +1150,5 @@ int kvm_trng_call(struct kvm_vcpu *vcpu);
>  void kvm_arm_vcpu_power_off(struct kvm_vcpu *vcpu);
>  bool kvm_arm_vcpu_stopped(struct kvm_vcpu *vcpu);
>
> +#endif /* __KVM__ */
>  #endif /* __ARM64_KVM_HOST_H__ */
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 96a80e8f6226..9d8c92cda3b6 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -125,6 +125,8 @@ void kvm_update_va_mask(struct alt_instr *alt,
>  void kvm_compute_layout(void);
>  void kvm_apply_hyp_relocations(void);
>
> +#ifdef __KVM__
> +
>  #define __hyp_pa(x) (((phys_addr_t)(x)) + hyp_physvirt_offset)
>
>  static __always_inline unsigned long __kern_hyp_va(unsigned long v)
> @@ -314,5 +316,7 @@ static inline struct kvm *kvm_s2_mmu_to_kvm(struct kvm_s2_mmu *mmu)
>  {
>         return container_of(mmu->arch, struct kvm, arch);
>  }
> +
> +#endif /* __KVM__ */
>  #endif /* __ASSEMBLY__ */
>  #endif /* __ARM64_KVM_MMU_H__ */
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 5ff1942b04fc..dc02ea9a002c 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -7,6 +7,8 @@
>   * Copyright (C) 2012 ARM Ltd.
>   */
>
> +#define __KVM__
> +
>  #include <linux/arm_sdei.h>
>  #include <linux/sched.h>
>  #include <linux/ftrace.h>
> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> index 4ce8c86967b5..99982b75671a 100644
> --- a/arch/arm64/kvm/hyp/Makefile
> +++ b/arch/arm64/kvm/hyp/Makefile
> @@ -5,6 +5,6 @@
>
>  incdir := $(srctree)/$(src)/include
>  subdir-asflags-y := -I$(incdir) -I$(srctree)/arch/arm64/kvm
> -subdir-ccflags-y := -I$(incdir) -I$(srctree)/arch/arm64/kvm
> +subdir-ccflags-y := -I$(incdir) -I$(srctree)/arch/arm64/kvm -D__KVM__
>
>  obj-$(CONFIG_KVM) += vhe/ nvhe/ pgtable.o
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index 2250253a6429..b5f4750fa16e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -9,7 +9,8 @@ asflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS
>  # there is no way to execute them and any such MMIO access from nVHE KVM
>  # will explode instantly (Words of Marc Zyngier). So introduce a generic flag
>  # __DISABLE_TRACE_MMIO__ to disable MMIO tracing for nVHE KVM.
> -ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS -D__DISABLE_TRACE_MMIO__
> +ccflags-y := -D__KVM_NVHE_HYPERVISOR__ -D__DISABLE_EXPORTS \
> +            -D__DISABLE_TRACE_MMIO__  -D__KVM__
>  ccflags-y += -fno-stack-protector      \
>              -DDISABLE_BRANCH_PROFILING \
>              $(DISABLE_STACKLEAK_PLUGIN)
> diff --git a/arch/arm64/kvm/hyp/vhe/Makefile b/arch/arm64/kvm/hyp/vhe/Makefile
> index 3b9e5464b5b3..54cd3c444102 100644
> --- a/arch/arm64/kvm/hyp/vhe/Makefile
> +++ b/arch/arm64/kvm/hyp/vhe/Makefile
> @@ -4,7 +4,7 @@
>  #
>
>  asflags-y := -D__KVM_VHE_HYPERVISOR__
> -ccflags-y := -D__KVM_VHE_HYPERVISOR__
> +ccflags-y := -D__KVM_VHE_HYPERVISOR__ -D__KVM__
>
>  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o
>  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
> diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
> index f8f63d0aa399..6fd7c998d7b9 100644
> --- a/arch/mips/include/asm/kvm_host.h
> +++ b/arch/mips/include/asm/kvm_host.h
> @@ -25,6 +25,7 @@
>  #include <asm/inst.h>
>  #include <asm/mipsregs.h>
>
> +#ifdef __KVM__
>  /* MIPS KVM register ids */
>  #define MIPS_CP0_32(_R, _S)                                    \
>         (KVM_REG_MIPS_CP0 | KVM_REG_SIZE_U32 | (8 * (_R) + (_S)))
> @@ -897,4 +898,5 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>
>  #define __KVM_HAVE_ARCH_FLUSH_REMOTE_TLBS
>
> +#endif /* __KVM__ */
>  #endif /* __MIPS_KVM_HOST_H__ */
> diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c
> index d1b11f66f748..8a233bddfea0 100644
> --- a/arch/mips/kernel/asm-offsets.c
> +++ b/arch/mips/kernel/asm-offsets.c
> @@ -9,6 +9,8 @@
>   * Kevin Kissell, kevink@xxxxxxxx and Carsten Langgaard, carstenl@xxxxxxxx
>   * Copyright (C) 2000 MIPS Technologies, Inc.
>   */
> +#define __KVM__
> +
>  #include <linux/compat.h>
>  #include <linux/types.h>
>  #include <linux/sched.h>
> diff --git a/arch/powerpc/include/asm/kvm_book3s.h b/arch/powerpc/include/asm/kvm_book3s.h
> index bbf5e2c5fe09..8880bc7c8a32 100644
> --- a/arch/powerpc/include/asm/kvm_book3s.h
> +++ b/arch/powerpc/include/asm/kvm_book3s.h
> @@ -13,6 +13,8 @@
>  #include <linux/kvm_host.h>
>  #include <asm/kvm_book3s_asm.h>
>
> +#ifdef __KVM__
> +
>  struct kvmppc_bat {
>         u64 raw;
>         u32 bepi;
> @@ -483,4 +485,5 @@ static inline u32 kvmppc_pack_vcpu_id(struct kvm *kvm, u32 id)
>         return packed_id;
>  }
>
> +#endif /* __KVM__ */
>  #endif /* __ASM_KVM_BOOK3S_H__ */
> diff --git a/arch/powerpc/include/asm/kvm_book3s_64.h b/arch/powerpc/include/asm/kvm_book3s_64.h
> index d49065af08e9..a807716ccae6 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_64.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_64.h
> @@ -16,6 +16,7 @@
>  #include <asm/ppc-opcode.h>
>  #include <asm/pte-walk.h>
>
> +#ifdef __KVM__
>  /*
>   * Structure for a nested guest, that is, for a guest that is managed by
>   * one of our guests.
> @@ -679,4 +680,5 @@ extern pte_t *find_kvm_nested_guest_pte(struct kvm *kvm, unsigned long lpid,
>
>  #endif /* CONFIG_KVM_BOOK3S_HV_POSSIBLE */
>
> +#endif /* __KVM__ */
>  #endif /* __ASM_KVM_BOOK3S_64_H__ */
> diff --git a/arch/powerpc/include/asm/kvm_booke.h b/arch/powerpc/include/asm/kvm_booke.h
> index 0c3401b2e19e..85ebc0314539 100644
> --- a/arch/powerpc/include/asm/kvm_booke.h
> +++ b/arch/powerpc/include/asm/kvm_booke.h
> @@ -12,6 +12,8 @@
>  #include <linux/types.h>
>  #include <linux/kvm_host.h>
>
> +#ifdef __KVM__
> +
>  /*
>   * Number of available lpids. Only the low-order 6 bits of LPID rgister are
>   * implemented on e500mc+ cores.
> @@ -105,4 +107,6 @@ static inline bool kvmppc_supports_magic_page(struct kvm_vcpu *vcpu)
>         return false;
>  #endif
>  }
> +
> +#endif /* __KVM__ */
>  #endif /* __ASM_KVM_BOOKE_H__ */
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 14ee0dece853..1e7a008ce085 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -14,6 +14,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/types.h>
>  #include <linux/kvm_types.h>
> +#include <linux/mmu_notifier.h>
>  #include <linux/threads.h>
>  #include <linux/spinlock.h>
>  #include <linux/kvm_para.h>
> @@ -25,13 +26,14 @@
>  #include <asm/cacheflush.h>
>  #include <asm/hvcall.h>
>  #include <asm/mce.h>
> +#include <asm/cputhreads.h>
>
> +#ifdef __KVM__
>  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
>
>  #define KVM_MAX_VCPUS          NR_CPUS
>  #define KVM_MAX_VCORES         NR_CPUS
>
> -#include <asm/cputhreads.h>
>
>  #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>  #include <asm/kvm_book3s_asm.h>                /* for MAX_SMT_THREADS */
> @@ -60,8 +62,6 @@
>  #define KVM_REQ_EPR_EXIT       KVM_ARCH_REQ(1)
>  #define KVM_REQ_PENDING_TIMER  KVM_ARCH_REQ(2)
>
> -#include <linux/mmu_notifier.h>
> -
>  #define KVM_ARCH_WANT_MMU_NOTIFIER
>
>  #define HPTEG_CACHE_NUM                        (1 << 15)
> @@ -883,4 +883,5 @@ static inline void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu) {}
>  static inline void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) {}
>  static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>
> +#endif /* __KVM__ */
>  #endif /* __POWERPC_KVM_HOST_H__ */
> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
> index ead2ad892ebc..03d9998d0111 100644
> --- a/arch/powerpc/include/asm/kvm_ppc.h
> +++ b/arch/powerpc/include/asm/kvm_ppc.h
> @@ -183,6 +183,7 @@ static inline void kvmppc_clear_host_ipi(int cpu)
>  static inline bool kvm_hv_mode_active(void)            { return false; }
>  #endif
>
> +#ifdef __KVM__
>  /*
>   * KVMPPC_INST_SW_BREAKPOINT is debug Instruction
>   * for supporting software breakpoint.
> @@ -1076,4 +1077,5 @@ static inline ulong kvmppc_get_ea_indexed(struct kvm_vcpu *vcpu, int ra, int rb)
>         return ea;
>  }
>
> +#endif /* __KVM__ */
>  #endif /* __POWERPC_KVM_PPC_H__ */
> diff --git a/arch/powerpc/kernel/asm-offsets.c b/arch/powerpc/kernel/asm-offsets.c
> index 9f14d95b8b32..872d44971536 100644
> --- a/arch/powerpc/kernel/asm-offsets.c
> +++ b/arch/powerpc/kernel/asm-offsets.c
> @@ -8,6 +8,7 @@
>   * compile this file to assembler, and then extract the
>   * #defines from the assembly-language output.
>   */
> +#define __KVM__
>
>  #include <linux/compat.h>
>  #include <linux/signal.h>
> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h
> index 1ebf20dfbaa6..a81ae8c4b739 100644
> --- a/arch/riscv/include/asm/kvm_host.h
> +++ b/arch/riscv/include/asm/kvm_host.h
> @@ -22,6 +22,8 @@
>  #include <asm/kvm_vcpu_timer.h>
>  #include <asm/kvm_vcpu_pmu.h>
>
> +#ifdef __KVM__
> +
>  #define KVM_MAX_VCPUS                  1024
>
>  #define KVM_HALT_POLL_NS_DEFAULT       500000
> @@ -354,4 +356,5 @@ bool kvm_riscv_vcpu_has_interrupts(struct kvm_vcpu *vcpu, u64 mask);
>  void kvm_riscv_vcpu_power_off(struct kvm_vcpu *vcpu);
>  void kvm_riscv_vcpu_power_on(struct kvm_vcpu *vcpu);
>
> +#endif /* __KVM__ */
>  #endif /* __RISCV_KVM_HOST_H__ */
> diff --git a/arch/riscv/kernel/asm-offsets.c b/arch/riscv/kernel/asm-offsets.c
> index d6a75aac1d27..476263e78f39 100644
> --- a/arch/riscv/kernel/asm-offsets.c
> +++ b/arch/riscv/kernel/asm-offsets.c
> @@ -5,6 +5,7 @@
>   */
>
>  #define GENERATING_ASM_OFFSETS
> +#define __KVM__
>
>  #include <linux/kbuild.h>
>  #include <linux/mm.h>
> diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
> index 427f9528a7b6..9153420bb5ac 100644
> --- a/arch/s390/include/asm/kvm_host.h
> +++ b/arch/s390/include/asm/kvm_host.h
> @@ -380,6 +380,10 @@ struct sie_page {
>         __u8 reserved700[2304];         /* 0x0700 */
>  };
>
> +extern char sie_exit;
> +
> +#ifdef __KVM__
> +
>  struct kvm_vcpu_stat {
>         struct kvm_vcpu_stat_generic generic;
>         u64 exit_userspace;
> @@ -1028,8 +1032,6 @@ static inline int sie64a(struct kvm_s390_sie_block *sie_block, u64 *rsa)
>         return __sie64a(virt_to_phys(sie_block), sie_block, rsa);
>  }
>
> -extern char sie_exit;
> -
>  bool kvm_s390_pv_is_protected(struct kvm *kvm);
>  bool kvm_s390_pv_cpu_is_protected(struct kvm_vcpu *vcpu);
>
> @@ -1049,6 +1051,7 @@ static inline void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) {}
>
>  #define __KVM_HAVE_ARCH_VM_FREE
>  void kvm_arch_free_vm(struct kvm *kvm);
> +#endif /* __KVM__ */
>
>  struct zpci_kvm_hook {
>         int (*kvm_register)(void *opaque, struct kvm *kvm);
> diff --git a/arch/s390/kernel/asm-offsets.c b/arch/s390/kernel/asm-offsets.c
> index fa5f6885c74a..22ed673871ee 100644
> --- a/arch/s390/kernel/asm-offsets.c
> +++ b/arch/s390/kernel/asm-offsets.c
> @@ -6,6 +6,7 @@
>   */
>
>  #define ASM_OFFSETS_C
> +#define __KVM__
>
>  #include <linux/kbuild.h>
>  #include <linux/kvm_host.h>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 29db870dbaae..eda45a937666 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -37,6 +37,8 @@
>  #include <asm/kvm_vcpu_regs.h>
>  #include <asm/hyperv-tlfs.h>
>
> +#ifdef __KVM__
> +
>  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
>
>  #define KVM_MAX_VCPUS 1024
> @@ -2229,4 +2231,5 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
>   */
>  #define KVM_EXIT_HYPERCALL_MBZ         GENMASK_ULL(31, 1)
>
> +#endif /* __KVM__ */
>  #endif /* _ASM_X86_KVM_HOST_H */
> diff --git a/drivers/s390/crypto/vfio_ap_drv.c b/drivers/s390/crypto/vfio_ap_drv.c
> index a5ab03e42ff1..55744f0f4758 100644
> --- a/drivers/s390/crypto/vfio_ap_drv.c
> +++ b/drivers/s390/crypto/vfio_ap_drv.c
> @@ -7,6 +7,7 @@
>   * Author(s): Tony Krowiak <akrowiak@xxxxxxxxxxxxx>
>   *           Pierre Morel <pmorel@xxxxxxxxxxxxx>
>   */
> +#define __KVM__
>
>  #include <linux/module.h>
>  #include <linux/mod_devicetable.h>
> diff --git a/drivers/s390/crypto/vfio_ap_ops.c b/drivers/s390/crypto/vfio_ap_ops.c
> index 4db538a55192..0dd98f42e9d5 100644
> --- a/drivers/s390/crypto/vfio_ap_ops.c
> +++ b/drivers/s390/crypto/vfio_ap_ops.c
> @@ -8,6 +8,8 @@
>   *           Halil Pasic <pasic@xxxxxxxxxxxxx>
>   *           Pierre Morel <pmorel@xxxxxxxxxxxxx>
>   */
> +#define __KVM__
> +
>  #include <linux/string.h>
>  #include <linux/vfio.h>
>  #include <linux/device.h>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index d520d6801070..f0afe549c0d6 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -45,6 +45,8 @@
>  #include <asm/kvm_host.h>
>  #include <linux/kvm_dirty_ring.h>
>
> +#ifdef __KVM__
> +
>  #ifndef KVM_MAX_VCPU_IDS
>  #define KVM_MAX_VCPU_IDS KVM_MAX_VCPUS
>  #endif
> @@ -2329,4 +2331,6 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
>  /* Max number of entries allowed for each kvm dirty ring */
>  #define  KVM_DIRTY_RING_MAX_ENTRIES  65536
>
> +#endif /* __KVM__ */
> +
>  #endif
> diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
> index 6f4737d5046a..4804bce2a655 100644
> --- a/include/linux/kvm_types.h
> +++ b/include/linux/kvm_types.h
> @@ -48,6 +48,8 @@ typedef u64            hfn_t;
>
>  typedef hfn_t kvm_pfn_t;
>
> +#ifdef __KVM__
> +
>  enum pfn_cache_usage {
>         KVM_GUEST_USES_PFN = BIT(0),
>         KVM_HOST_USES_PFN  = BIT(1),
> @@ -123,4 +125,5 @@ struct kvm_vcpu_stat_generic {
>
>  #define KVM_STATS_NAME_SIZE    48
>
> +#endif /* __KVM__ */
>  #endif /* __KVM_TYPES_H__ */
> diff --git a/include/trace/events/kvm.h b/include/trace/events/kvm.h
> index 3bd31ea23fee..aee85527bb74 100644
> --- a/include/trace/events/kvm.h
> +++ b/include/trace/events/kvm.h
> @@ -2,8 +2,13 @@
>  #if !defined(_TRACE_KVM_MAIN_H) || defined(TRACE_HEADER_MULTI_READ)
>  #define _TRACE_KVM_MAIN_H
>
> +#include <linux/kvm_host.h>
>  #include <linux/tracepoint.h>
>
> +#ifndef __KVM__
> +static_assert(0, "Do not include trace/events/kvm.h from non-KVM code");
> +#endif
> +
>  #undef TRACE_SYSTEM
>  #define TRACE_SYSTEM kvm
>
> diff --git a/virt/kvm/Makefile.kvm b/virt/kvm/Makefile.kvm
> index e85079ad245d..4de10d447ef3 100644
> --- a/virt/kvm/Makefile.kvm
> +++ b/virt/kvm/Makefile.kvm
> @@ -3,7 +3,7 @@
>  # Makefile for Kernel-based Virtual Machine module
>  #
>
> -ccflags-y += -I$(srctree)/$(src)
> +ccflags-y += -I$(srctree)/$(src) -D__KVM__
>
>  KVM ?= ../../../virt/kvm
>
> --
> 2.42.0.459.ge4e396fd5e-goog
>