KVM: x86 emulator: simplify read_emulated

No need split mmio read region into 8-bits pieces since we do it in
emulator_read_write_onepage

Changelog:
  Add a WARN_ON to check read-cache overflow

Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 14 insertions, 17 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 85b611e13e84..2c5d1e65d9d1 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -1166,24 +1166,21 @@ static int read_emulated(struct x86_emulate_ctxt *ctxt,
         int rc;
         struct read_cache *mc = &ctxt->mem_read;
 
-        while (size) {
-                int n = min(size, 8u);
-                size -= n;
-                if (mc->pos < mc->end)
-                        goto read_cached;
-
-                rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, n,
-                                              &ctxt->exception);
-                if (rc != X86EMUL_CONTINUE)
-                        return rc;
-                mc->end += n;
+        if (mc->pos < mc->end)
+                goto read_cached;
 
-        read_cached:
-                memcpy(dest, mc->data + mc->pos, n);
-                mc->pos += n;
-                dest += n;
-                addr += n;
-        }
+        WARN_ON((mc->end + size) >= sizeof(mc->data));
+
+        rc = ctxt->ops->read_emulated(ctxt, addr, mc->data + mc->end, size,
+                                      &ctxt->exception);
+        if (rc != X86EMUL_CONTINUE)
+                return rc;
+
+        mc->end += size;
+
+read_cached:
+        memcpy(dest, mc->data + mc->pos, size);
+        mc->pos += size;
         return X86EMUL_CONTINUE;
 }