[PATCH] KVM: Access registers for instructions with ModR/M byte and Mod = 3

[Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>]

On Wed, Oct 17, 2007 at 06:23:41PM +0200, Aurelien Jarno wrote:
> >> The 0F 01 instruction is then correctly emulated, but another of this
> > Oops s/0F 01/invlpg/
> >> group is probably not, as the patch clearly fix the problem on AMD.
> > 
> 
> I confirm the problem. SVM does not virtualize smsw and lmsw that have
> to be emulated. And it looks like the decoding or/and emulation of those
> instructions is currently broken in KVM.
>

Ok, next try. This time I have opened the IA32 manual (I should have
done that before), so I hope it is correct.


KVM: Access registers for instructions with ModR/M byte and Mod = 3

The patch belows changes the access type to register from memory for 
instructions that are declared as SrcMem or DstMem, but have a 
ModR/M byte with Mod = 3.

It fixes (at least) the lmsw and smsw instructions on an AMD64 CPU,
which are needed for FreeBSD.

Signed-off-by: Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index e974ace..005e57c 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -831,6 +831,12 @@ modrm_done:
 		if (c->twobyte && c->b == 0x01
 				    && c->modrm_reg == 7)
 			break;
+		/* For instructions with a ModR/M byte, switch to register
+		   access if Mod = 3. */
+		if ((c->d & ModRM) && c->modrm_mod == 3) {
+			c->src.type = OP_REG;
+			break;
+		}
 srcmem_common:
 		c->src.type = OP_MEM;
 		break;
@@ -893,7 +899,12 @@ srcmem_common:
 		}
 		break;
 	case DstMem:
-		c->dst.type = OP_MEM;
+		/* For instructions with a ModR/M byte, switch to register
+		   access if Mod = 3. */
+		if ((c->d & ModRM) && c->modrm_mod == 3)
+			c->dst.type = OP_REG;
+		else
+			c->dst.type = OP_MEM;
 		break;
 	}
 

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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