KVM: x86 emulator: add support for writing back the source operand

Some instructions write back the source operand, not just the destination.
Add support for doing this via the decode flags.

Gleb: add BUG_ON() to prevent source to be memory operand.

Signed-off-by: Avi Kivity <avi.kivity@gmail.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8db0010ed150d5c1fa1d0b6aa96668587c2d1004..a4c266e99e5032b8a024f9d3153b613020e2fe98 100644 (file)
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -155,6 +155,7 @@
 #define Avx         ((u64)1 << 43)  /* Advanced Vector Extensions */
 #define Fastop      ((u64)1 << 44)  /* Use opcode::u.fastop */
 #define NoWrite     ((u64)1 << 45)  /* No writeback */
+#define SrcWrite    ((u64)1 << 46)  /* Write back src operand */
 
 #define X2(x...) x, x
 #define X3(x...) X2(x), x
@@ -1723,45 +1724,42 @@ static void write_register_operand(struct operand *op)
        }
 }
 
-static int writeback(struct x86_emulate_ctxt *ctxt)
+static int writeback(struct x86_emulate_ctxt *ctxt, struct operand *op)
 {
        int rc;
 
-       if (ctxt->d & NoWrite)
-               return X86EMUL_CONTINUE;
-
-       switch (ctxt->dst.type) {
+       switch (op->type) {
        case OP_REG:
-               write_register_operand(&ctxt->dst);
+               write_register_operand(op);
                break;
        case OP_MEM:
                if (ctxt->lock_prefix)
                        rc = segmented_cmpxchg(ctxt,
-                                              ctxt->dst.addr.mem,
-                                              &ctxt->dst.orig_val,
-                                              &ctxt->dst.val,
-                                              ctxt->dst.bytes);
+                                              op->addr.mem,
+                                              &op->orig_val,
+                                              &op->val,
+                                              op->bytes);
                else
                        rc = segmented_write(ctxt,
-                                            ctxt->dst.addr.mem,
-                                            &ctxt->dst.val,
-                                            ctxt->dst.bytes);
+                                            op->addr.mem,
+                                            &op->val,
+                                            op->bytes);
                if (rc != X86EMUL_CONTINUE)
                        return rc;
                break;
        case OP_MEM_STR:
                rc = segmented_write(ctxt,
-                               ctxt->dst.addr.mem,
-                               ctxt->dst.data,
-                               ctxt->dst.bytes * ctxt->dst.count);
+                               op->addr.mem,
+                               op->data,
+                               op->bytes * op->count);
                if (rc != X86EMUL_CONTINUE)
                        return rc;
                break;
        case OP_XMM:
-               write_sse_reg(ctxt, &ctxt->dst.vec_val, ctxt->dst.addr.xmm);
+               write_sse_reg(ctxt, &op->vec_val, op->addr.xmm);
                break;
        case OP_MM:
-               write_mmx_reg(ctxt, &ctxt->dst.mm_val, ctxt->dst.addr.mm);
+               write_mmx_reg(ctxt, &op->mm_val, op->addr.mm);
                break;
        case OP_NONE:
                /* no writeback */
@@ -4769,9 +4767,17 @@ special_insn:
                goto done;
 
 writeback:
-       rc = writeback(ctxt);
-       if (rc != X86EMUL_CONTINUE)
-               goto done;
+       if (!(ctxt->d & NoWrite)) {
+               rc = writeback(ctxt, &ctxt->dst);
+               if (rc != X86EMUL_CONTINUE)
+                       goto done;
+       }
+       if (ctxt->d & SrcWrite) {
+               BUG_ON(ctxt->src.type == OP_MEM || ctxt->src.type == OP_MEM_STR);
+               rc = writeback(ctxt, &ctxt->src);
+               if (rc != X86EMUL_CONTINUE)
+                       goto done;
+       }
 
        /*
         * restore dst type in case the decoding will be reused