kvm, emulator: Use opcode length

Add a field to the current emulation context which contains the
instruction opcode length. This will streamline handling of opcodes of
different length.

Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 11 insertions, 6 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 15f960c06ff7..92a176ad456c 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -279,8 +279,12 @@ struct x86_emulate_ctxt {
         bool have_exception;
         struct x86_exception exception;
 
-        /* decode cache */
-        u8 twobyte;
+        /*
+         * decode cache
+         */
+
+        /* current opcode length in bytes */
+        u8 opcode_len;
         u8 b;
         u8 intercept;
         u8 lock_prefix;
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ddc3f3d2afdb..d554d96afbca 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4126,6 +4126,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
         ctxt->_eip = ctxt->eip;
         ctxt->fetch.start = ctxt->_eip;
         ctxt->fetch.end = ctxt->fetch.start + insn_len;
+        ctxt->opcode_len = 1;
         if (insn_len > 0)
                 memcpy(ctxt->fetch.data, insn, insn_len);
 
@@ -4208,7 +4209,7 @@ done_prefixes:
         opcode = opcode_table[ctxt->b];
         /* Two-byte opcode? */
         if (ctxt->b == 0x0f) {
-                ctxt->twobyte = 1;
+                ctxt->opcode_len = 2;
                 ctxt->b = insn_fetch(u8, ctxt);
                 opcode = twobyte_table[ctxt->b];
         }
@@ -4540,7 +4541,7 @@ special_insn:
                 goto writeback;
         }
 
-        if (ctxt->twobyte)
+        if (ctxt->opcode_len == 2)
                 goto twobyte_insn;
 
         switch (ctxt->b) {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3d1e3ee8b39e..d00d88455fef 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4789,8 +4789,8 @@ static void inject_emulated_exception(struct kvm_vcpu *vcpu)
 
 static void init_decode_cache(struct x86_emulate_ctxt *ctxt)
 {
-        memset(&ctxt->twobyte, 0,
-               (void *)&ctxt->_regs - (void *)&ctxt->twobyte);
+        memset(&ctxt->opcode_len, 0,
+               (void *)&ctxt->_regs - (void *)&ctxt->opcode_len);
 
         ctxt->fetch.start = 0;
         ctxt->fetch.end = 0;