Re: [Xen-devel] Xen 4.0.0-rc7 problem/hang with vt-d DMAR parsing

[Weidong Han <weidong.han@xxxxxxxxx>]

Jan Beulich wrote:
> > > > "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> 24.03.10 02:52 >>>
> > > >         
> > Pasi K?rkk?inen wrote:
> >     
> > > Hmm.. wondering if the patch Jan just sent will help with that.
> > > Sounds like it might help :)
> > >       
> > I guess Jan's patch helps here in a very interesting way:
> >     
> I think reference was to a patch I sent yesterday, which I don't think
> would help here (as the box would have to crash for it to help).
>
>   
> > I suspect your BIOS doesn't construct the DMAR properly, e.g., in acpi_parse_dmar(),  
> > entry_header->length is always 0, so xen'll hang in the while loop and continue printing the 
> > "dmaru->address = 0" message when iommu=verbose.
> >     
> Surely entry_header->length == 0 (or really
> entry_header->length < sizeof(struct acpi_table_XXX)) should be
> considered invalid, and hence get checked for? Linux at least has
> a check against zero here...
>   
yes,  we need the check to solve Pasi's issue. I ported the patch from 
Linux, post below. Pasi, pls test the patch on your machine.
it cannot check entry_header->length < sizeof(struct acpi_table_XXX), 
which is not the actual size in acpi table.
diff -r a4eac162dcb9 xen/drivers/passthrough/vtd/dmar.c
--- a/xen/drivers/passthrough/vtd/dmar.c    Thu Mar 25 01:05:03 2010 +0800
+++ b/xen/drivers/passthrough/vtd/dmar.c    Thu Mar 25 01:54:31 2010 +0800
@@ -659,6 +659,15 @@ static int __init acpi_parse_dmar(struct
    while ( ((unsigned long)entry_header) <
            (((unsigned long)dmar) + table->length) )
    {
+        /* Avoid looping forever on bad ACPI tables */
+        if ( entry_header->length == 0 )
+        {
+            dprintk(XENLOG_WARNING VTDPREFIX,
+                    "Invalid 0-length entry_header\n");
+            ret = -EINVAL;
+            break;
+        }
+
        switch ( entry_header->type )
        {
        case ACPI_DMAR_DRHD:


>   
> > Without verbose message outputing, the loop runs even faster and in 
> > acpi_parse_one_drhd(),  xmalloc(struct acpi_drhd_unit) would NULL in a short 
> > periof of time and hence VT-d is got disabled... :-)
> >     
> Why would you expect xmalloc() to fail soon? This is only to be expected
> on a 32-bit system (which I doubt this one is).
>
> Jan
>
>   
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