Currently support to exit to userspace for private/shared memory
conversion.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Yu Zhang <redacted>
Signed-off-by: Chao Peng <redacted>
---
  arch/x86/kvm/mmu/mmu.c   | 20 ++++++++++++++++++++
  include/uapi/linux/kvm.h | 15 +++++++++++++++
  2 files changed, 35 insertions(+)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index af5ecf4ef62a..780868888aa8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c

@@ -3950,6 +3950,17 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
  
  	slot = __kvm_vcpu_gfn_to_memslot(vcpu, gfn, private);
  
+	/*
+	 * Exit to userspace to map the requested private/shared memory region
+	 * if there is no memslot and (a) the access is private or (b) there is
+	 * an existing private memslot.  Emulated MMIO must be accessed through
+	 * shared GPAs, thus a memslot miss on a private GPA is always handled
+	 * as an implicit conversion "request".
+	 */
+	if (!slot &&
+	    (private || __kvm_vcpu_gfn_to_memslot(vcpu, gfn, true)))
+		goto out_convert;
+
  	/* Don't expose aliases for no slot GFNs or private memslots */
  	if ((cr2_or_gpa & vcpu_gpa_stolen_mask(vcpu)) &&
  	    !kvm_is_visible_memslot(slot)) {

@@ -3994,6 +4005,15 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
  	*pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL,
  				    write, writable, hva);
  	return false;
+
+out_convert:
+	vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
+	vcpu->run->mem.type = private ? KVM_EXIT_MEM_MAP_PRIVATE
+				      : KVM_EXIT_MEM_MAP_SHARE;
+	vcpu->run->mem.u.map.gpa = cr2_or_gpa;
+	vcpu->run->mem.u.map.size = PAGE_SIZE;
+	return true;
+
  

}
  
  static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 8d20caae9180..470c472a9451 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h

@@ -233,6 +233,18 @@ struct kvm_xen_exit {
  	} u;
  };
  
+struct kvm_memory_exit {
+#define KVM_EXIT_MEM_MAP_SHARE          1
+#define KVM_EXIT_MEM_MAP_PRIVATE        2
+	__u32 type;
+	union {
+		struct {
+			__u64 gpa;
+			__u64 size;
+		} map;
+	} u;
+};
+
  #define KVM_S390_GET_SKEYS_NONE   1
  #define KVM_S390_SKEYS_MAX        1048576
  

@@ -272,6 +284,7 @@ struct kvm_xen_exit {
  #define KVM_EXIT_X86_BUS_LOCK     33
  #define KVM_EXIT_XEN              34
  #define KVM_EXIT_TDVMCALL         35
+#define KVM_EXIT_MEMORY_ERROR	  36
  
  /* For KVM_EXIT_INTERNAL_ERROR */
  /* Emulate instruction failed. */

@@ -455,6 +468,8 @@ struct kvm_run {
  			__u64 subfunc;
  			__u64 param[4];
  		} tdvmcall;
+		/* KVM_EXIT_MEMORY_ERROR */
+		struct kvm_memory_exit mem;
  		/* Fix the size of the union. */
  		char padding[256];
  	};