On 09/21/15 at 03:54pm, Joerg Roedel wrote:
> Hi Baoquan,
>
> On Tue, Sep 15, 2015 at 08:06:06PM +0800, Baoquan He wrote:
> > Recently I am free and can try to work out the amd-iommu support for
> > kdump kernel. Now I have some plans and draft them into codes and debugging.
> > And also there are prlblems. I brief them here, could you please have a
> > look and give some suggestions?
> >
> > Two parts:
> >
> > 1) IO page mapping
> > .> Checking if it's in kdump kernel and previously enabled
> > .> If yes do below operatons:
> > .> Do not disable amd iommu
> > .> Copy dev table form old kernel and set the old domain id in
> > amd_iommu_pd_alloc_bitmap
> > .> Don't call update_domain() to update device table until the first
> > __map_single() is called by device driver init
>
> These operations look good so far, but a problem still remains: The AMD
> IOMMU driver uses default domains which get allocated and initialized at
> iommu driver initialization time. So there is no clean way yet to defer
> device domain initialization to device driver init time.
It's so good to get your reply.
Check the code again, though default domains are allocated and
initialized at iommu driver initialization time, it may newly build or
change the io page tables, finally it need call update_domain() to
set domain->pt_root to dte entry. If I changed update_domain() like
below, then any change of io page mapping won't be installed into dte
entry of device, then it doesn't have effect, I think this can defer the
contents of io page tables installed to device driver init time when I
reset the translation_pre_enabled state to make update_main() work.
static void update_domain(struct protection_domain *domain)
{
if (!domain->updated || translation_pre_enabled())
return;
update_device_table(domain);
...
}
Don't know if I understand it correctly.
>
> This needs to be changed before the VT-d driver can be converted to
> default domains too.
>
> I'll also have a look into your patch. Maybe I see something that causes
> the interrupt to fail.
>
>
> Joerg
>
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