KVM: x86 emulator: Add Virtual-8086 mode of emulation

For some instructions CPU behaves differently for real-mode and
virtual 8086. Let emulator know which mode cpu is in, so it will
not poke into vcpu state directly.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Cc: stable@kernel.org
Signed-off-by: Avi Kivity <avi@redhat.com>

3 files changed, 10 insertions, 6 deletions

diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h
index 9b697c2735d9..784d7c586d8e 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -168,6 +168,7 @@ struct x86_emulate_ctxt {
 
 /* Execution mode, passed to the emulator. */
 #define X86EMUL_MODE_REAL     0 /* Real mode.             */
+#define X86EMUL_MODE_VM86     1 /* Virtual 8086 mode.     */
 #define X86EMUL_MODE_PROT16   2 /* 16-bit protected mode. */
 #define X86EMUL_MODE_PROT32   4 /* 32-bit protected mode. */
 #define X86EMUL_MODE_PROT64   8 /* 64-bit (long) mode.    */
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 45a4f7c1bb0b..e4e2df3b6038 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -899,6 +899,7 @@ x86_decode_insn(struct x86_emulate_ctxt *ctxt, struct x86_emulate_ops *ops)
 
         switch (mode) {
         case X86EMUL_MODE_REAL:
+        case X86EMUL_MODE_VM86:
         case X86EMUL_MODE_PROT16:
                 def_op_bytes = def_ad_bytes = 2;
                 break;
@@ -1525,7 +1526,7 @@ emulate_syscall(struct x86_emulate_ctxt *ctxt)
 
         /* syscall is not available in real mode */
         if (c->lock_prefix || ctxt->mode == X86EMUL_MODE_REAL
-            || !is_protmode(ctxt->vcpu))
+            || ctxt->mode == X86EMUL_MODE_VM86)
                 return -1;
 
         setup_syscalls_segments(ctxt, &cs, &ss);
@@ -1577,8 +1578,8 @@ emulate_sysenter(struct x86_emulate_ctxt *ctxt)
         if (c->lock_prefix)
                 return -1;
 
-        /* inject #GP if in real mode or paging is disabled */
-        if (ctxt->mode == X86EMUL_MODE_REAL || !is_protmode(ctxt->vcpu)) {
+        /* inject #GP if in real mode */
+        if (ctxt->mode == X86EMUL_MODE_REAL) {
                 kvm_inject_gp(ctxt->vcpu, 0);
                 return -1;
         }
@@ -1642,8 +1643,9 @@ emulate_sysexit(struct x86_emulate_ctxt *ctxt)
         if (c->lock_prefix)
                 return -1;
 
-        /* inject #GP if in real mode or paging is disabled */
-        if (ctxt->mode == X86EMUL_MODE_REAL || !is_protmode(ctxt->vcpu)) {
+        /* inject #GP if in real mode or Virtual 8086 mode */
+        if (ctxt->mode == X86EMUL_MODE_REAL ||
+            ctxt->mode == X86EMUL_MODE_VM86) {
                 kvm_inject_gp(ctxt->vcpu, 0);
                 return -1;
         }
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b2f91b9af00d..a28379507d30 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3348,8 +3348,9 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
                 vcpu->arch.emulate_ctxt.vcpu = vcpu;
                 vcpu->arch.emulate_ctxt.eflags = kvm_get_rflags(vcpu);
                 vcpu->arch.emulate_ctxt.mode =
+                        (!is_protmode(vcpu)) ? X86EMUL_MODE_REAL :
                         (vcpu->arch.emulate_ctxt.eflags & X86_EFLAGS_VM)
-                        ? X86EMUL_MODE_REAL : cs_l
+                        ? X86EMUL_MODE_VM86 : cs_l
                         ? X86EMUL_MODE_PROT64 : cs_db
                         ? X86EMUL_MODE_PROT32 : X86EMUL_MODE_PROT16;