Re: KVM 29: Page fault in kernel mode while booting GNU/kFreeBSD

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

On Fri, Jul 20, 2007 at 09:57:55AM +0300, Avi Kivity wrote:
> Avi Kivity wrote:
> >> Please tell me what I can do to help debugging this problem. 
> >> Alternatively I have uploaded an image to reproduce the problem here:
> >> http://temp.aurel32.net/kfreebsd-amd64.img.g
> >>     
> >
> > I've downloaded the image and booted it three times using kvm HEAD. 
> > Each time I got to the login prompt.
> >
> > Is this always reproducible?  Can you check with kvm HEAD (not that I
> > think of anything that could have fixed this).
> >
> >   
> 
> Sorry, that was on Intel.  It reproduces easily on AMD.

By comparing the cases were the old and the new condition are different,
I have found that the problem occurs for the lmsw and smsw instructions.

The patch below is very ugly, but it workarounds the problem.

diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 21ce977..6c1523f 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1206,11 +1206,13 @@ twobyte_insn:
 				goto cannot_emulate;
 			*(u16 *)&_regs[modrm_rm]
 				= realmode_get_cr(ctxt->vcpu, 0);
+			no_wb = 1;
 			break;
 		case 6: /* lmsw */
 			if (modrm_mod != 3)
 				goto cannot_emulate;
 			realmode_lmsw(ctxt->vcpu, (u16)modrm_val, &_eflags);
+			no_wb = 1;
 			break;
 		case 7: /* invlpg*/

-- 
  .''`.  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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