[PATCH v8 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit

[Chao Peng]

This new KVM exit allows userspace to handle memory-related errors. It
indicates an error happens in KVM at guest memory range [gpa, gpa+size).
The flags includes additional information for userspace to handle the
error. Currently bit 0 is defined as 'private memory' where '1'
indicates error happens due to private memory access and '0' indicates
error happens due to shared memory access.

When private memory is enabled, this new exit will be used for KVM to
exit to userspace for shared <-> private memory conversion in memory
encryption usage. In such usage, typically there are two kind of memory
conversions:
  - explicit conversion: happens when guest explicitly calls into KVM
    to map a range (as private or shared), KVM then exits to userspace
    to do the map/unmap operations.
  - implicit conversion: happens in KVM page fault handler where KVM
    exits to userspace for an implicit conversion when the page is in a
    different state than requested (private or shared).

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Co-developed-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
 Documentation/virt/kvm/api.rst | 23 +++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  9 +++++++++
 2 files changed, 32 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index c1fac1e9f820..1a6c003b2a0b 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6638,6 +6638,29 @@ array field represents return values. The userspace should update the return
 values of SBI call before resuming the VCPU. For more details on RISC-V SBI
 spec refer, https://github.com/riscv/riscv-sbi-doc.
 
+::
+
+		/* KVM_EXIT_MEMORY_FAULT */
+		struct {
+  #define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1 << 0)
+			__u32 flags;
+			__u32 padding;
+			__u64 gpa;
+			__u64 size;
+		} memory;
+
+If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
+encountered a memory error which is not handled by KVM kernel module and
+userspace may choose to handle it. The 'flags' field indicates the memory
+properties of the exit.
+
+ - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
+   private memory access when the bit is set otherwise the memory error is
+   caused by shared memory access when the bit is clear.
+
+'gpa' and 'size' indicate the memory range the error occurs at. The userspace
+may handle the error and return to KVM to retry the previous memory access.
+
 ::
 
     /* KVM_EXIT_NOTIFY */
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 3ef462fb3b2a..0c8db7b7c138 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -300,6 +300,7 @@ struct kvm_xen_exit {
 #define KVM_EXIT_RISCV_SBI        35
 #define KVM_EXIT_RISCV_CSR        36
 #define KVM_EXIT_NOTIFY           37
+#define KVM_EXIT_MEMORY_FAULT     38
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -538,6 +539,14 @@ struct kvm_run {
 #define KVM_NOTIFY_CONTEXT_INVALID	(1 << 0)
 			__u32 flags;
 		} notify;
+		/* KVM_EXIT_MEMORY_FAULT */
+		struct {
+#define KVM_MEMORY_EXIT_FLAG_PRIVATE	(1 << 0)
+			__u32 flags;
+			__u32 padding;
+			__u64 gpa;
+			__u64 size;
+		} memory;
 		/* Fix the size of the union. */
 		char padding[256];
 	};
-- 
2.25.1