[PATCH v7 10/14] 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.

After private memory is enabled, this new exit will be used for KVM to
exit to userspace for shared memory <-> 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.
    * if the fault is due to a private memory access then causes a
      userspace exit for a shared->private conversion when the page
      is recognized as shared by KVM.
    * If the fault is due to a shared memory access then causes a
      userspace exit for a private->shared conversion when the page
      is recognized as private by KVM.

Suggested-by: Sean Christopherson <seanjc@google.com>
Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
---
 Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
 include/uapi/linux/kvm.h       |  9 +++++++++
 2 files changed, 31 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 4f27c973a952..5ecfc7fbe0ee 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6583,6 +6583,28 @@ 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 c467c69b7ad7..83c278f284dd 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -299,6 +299,7 @@ struct kvm_xen_exit {
 #define KVM_EXIT_XEN              34
 #define KVM_EXIT_RISCV_SBI        35
 #define KVM_EXIT_NOTIFY           36
+#define KVM_EXIT_MEMORY_FAULT     37
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -530,6 +531,14 @@ 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