[RFC PATCH 5/6] kvm: x86: add KVM_EXIT_MEMORY_ERROR exit

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

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

Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
 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];
 	};
-- 
2.17.1