On Wed, Jul 25, 2007 at 06:14:20AM +0300, Avi Kivity wrote:
> Aurelien Jarno wrote:
> > 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.
> >
>
> Ah, I was looking at amd-specific instructions (vmx decodes lmsw) but
> missed these two. Good work.
>
> > The patch below is very ugly, but it workarounds the problem.
> >
>
> It's not ugly, it just lives in an ugly function. But it does lack a
> changelog and a signoff.
>
After a short discussion on IRC, it seems that all 0x02 0x01
instructions do not use the writeback. Please find an updated and
signedoff patch below.
KVM: disable writeback for 0x02 0x01 instructions.
0x02 0x01 instructions (ie lgdt, lidt, smsw, lmsw and invlpg) does
not use writeback. This patch set no_wb=1 when emulating those
instructions.
Signed-off-by: Aurelien Jarno <[EMAIL PROTECTED]>
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 21ce977..cbbb9c5 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1183,6 +1183,8 @@ pop_instruction:
twobyte_insn:
switch (b) {
case 0x01: /* lgdt, lidt, lmsw */
+ /* Disable writeback. */
+ no_wb = 1;
switch (modrm_reg) {
u16 size;
unsigned long address;
--
.''`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' [EMAIL PROTECTED] | [EMAIL PROTECTED]
`- people.debian.org/~aurel32 | www.aurel32.net
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