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>

1 files changed, 27 insertions, 21 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8db0010ed150..a4c266e99e50 100644
--- 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