The command is used to decrypt a page of guest memory for debug.

The command will be used by qemu monitor dump and gdbserver to access
the guest memory for debug purposes. A typical usage look like:

 cpu_physical_memory_rw_debug
   cpu_physical_memory_rw_debug_internal
     sev_debug_decrypt

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 sev.c |   36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/sev.c b/sev.c
index d32391e..f8d822d 100644
--- a/sev.c
+++ b/sev.c
@@ -320,6 +320,36 @@ err_1:
 }
 
 static int
+sev_debug_decrypt(SEVState *s, uint8_t *dst, const uint8_t *src, uint32_t len)
+{
+    int ret, error;
+    struct kvm_sev_dbg *dbg;
+
+    if (!s) {
+        return 1;
+    }
+
+    dbg = g_malloc0(sizeof(*dbg));
+    if (!dbg) {
+        return 1;
+    }
+
+    dbg->src_addr = (unsigned long)src;
+    dbg->dst_addr = (unsigned long)dst;
+    dbg->length = len;
+
+    ret = sev_ioctl(KVM_SEV_DBG_DECRYPT, dbg, &error);
+    if (ret) {
+        fprintf(stderr, "failed DBG_DECRYPT %d (%#x)\n", ret, error);
+        goto err;
+    }
+
+err:
+    g_free(dbg);
+    return ret;
+}
+
+static int
 sev_mem_write(uint8_t *dst, const uint8_t *src, uint32_t len, MemTxAttrs attrs)
 {
     SEVState *s = kvm_memcrypt_get_handle();
@@ -335,7 +365,11 @@ sev_mem_write(uint8_t *dst, const uint8_t *src, uint32_t len, MemTxAttrs attrs)
 static int
 sev_mem_read(uint8_t *dst, const uint8_t *src, uint32_t len, MemTxAttrs attrs)
 {
-    return 0;
+    SEVState *s = kvm_memcrypt_get_handle();
+
+    assert(attrs.debug);
+
+    return sev_debug_decrypt(s, dst, src, len);
 }
 
 void *