[RFC PATCH 1/8] KVM: Document KVM_MAP_MEMORY ioctl

[isaku.yamahata@intel.com]

From: Isaku Yamahata <isaku.yamahata@intel.com>

Adds documentation of KVM_MAP_MEMORY ioctl.

It pre-populates guest memory. And potentially do initialized memory
contents with encryption and measurement depending on underlying
technology.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 Documentation/virt/kvm/api.rst | 36 ++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index 0b5a33ee71ee..33d2b63f7dbf 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6352,6 +6352,42 @@ a single guest_memfd file, but the bound ranges must not overlap).
 
 See KVM_SET_USER_MEMORY_REGION2 for additional details.
 
+4.143 KVM_MAP_MEMORY
+------------------------
+
+:Capability: KVM_CAP_MAP_MEMORY
+:Architectures: none
+:Type: vcpu ioctl
+:Parameters: struct kvm_memory_mapping(in/out)
+:Returns: 0 on success, <0 on error
+
+KVM_MAP_MEMORY populates guest memory without running vcpu.
+
+::
+
+  struct kvm_memory_mapping {
+	__u64 base_gfn;
+	__u64 nr_pages;
+	__u64 flags;
+	__u64 source;
+  };
+
+  /* For kvm_memory_mapping:: flags */
+  #define KVM_MEMORY_MAPPING_FLAG_WRITE         _BITULL(0)
+  #define KVM_MEMORY_MAPPING_FLAG_EXEC          _BITULL(1)
+  #define KVM_MEMORY_MAPPING_FLAG_USER          _BITULL(2)
+  #define KVM_MEMORY_MAPPING_FLAG_PRIVATE       _BITULL(3)
+
+KVM_MAP_MEMORY populates guest memory in the underlying mapping. If source is
+not zero and it's supported (depending on underlying technology), the guest
+memory content is populated with the source.  The flags field supports three
+flags: KVM_MEMORY_MAPPING_FLAG_WRITE, KVM_MEMORY_MAPPING_FLAG_EXEC, and
+KVM_MEMORY_MAPPING_FLAG_USER.  Which corresponds to fault code for kvm page
+fault to populate guest memory. write fault, fetch fault and user fault.
+When it returned, the input is updated.  If nr_pages is large, it may
+return -EAGAIN and update the values (base_gfn and nr_pages. source if not zero)
+to point the remaining range.
+
 5. The kvm_run structure
 ========================
 
-- 
2.25.1