Re: [Xen-devel] [PATCH V2] x86/AMD-Vi: Add additional check for invalid special->handle

[Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>]

On 8/29/2013 2:17 AM, Jan Beulich wrote:
> > > > On 28.08.13 at 19:34, <suravee.suthikulpanit@xxxxxxx> wrote:
> > From: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> >
> > This patch add an additional logic to check for the often case when the
> > special->handle is not initialized due to firmware bugs.
> > but the special->usedid is correct. If users overide this using the
> > command line option ivrs_ioapic, then it should use the value instead.
> > ---
> > This patch is supposed to follow the patches:
> > [Xen-devel] [PATCH RFC 2/2] AMD IOMMU: allow command line overrides for
> > broken IVRS tables
> >
> > Changes in V2:
> >         - Fix logic to match the special->used_id with the value provided by 
> > users.
> As said in a previous reply - I'm convinced we can't fix things both
> ways with just a single command line option: We need to know
> which value to use as anchor (I'd generally think that ought to be
> the value inside the square backets) and which value to use as
> overrides.
>
> And since my earlier patch was inspired by the Linux one - I don't
> think Linux allows fixing up things the way you try to here either.
>
> Jan
Actually, on Linux, the it would try matching the handle (i.e. the value 
in the square bracket).  If it is specified via command line, it will 
override the value in the IVRS.  In case the entry contains the handle 
value which is not list as IOAPIC in the ACPI APIC table, we should be 
able to invalidate the entry.  This same rule should also apply when 
users specify invalid handle value.  Also, I never see the case where 
the special->used_id is incorrect. The other case I am seeing is when 
the IVRS special entry is missing for IOAPIC, which this should already 
be handled in your original patch.
I have also verified that this works on Linux.  For example, on my 
system, there are 2 IOAPICs with APIC ID 8 and 9 according to the ACPI 
APIC table.  However, in IVRS, the value in both special entries are 
0xff.  When I give the boot options "ivrs_ioapic[8]=00:14.0 
ivrs_ioapic[9]=00:0.1", this allows IOMMU to initialize correctly.
Suravee


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