RE: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and early_acpi_os_unmap_memory() from Linux kernel

[Zheng, Lv]

Hi,

> From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-owner@xxxxxxxxxxxxxxx] On Behalf Of Zheng,
> Lv
> Subject: RE: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and
> early_acpi_os_unmap_memory() from Linux kernel
> 
> Hi,
> 
> > From: linux-acpi-owner@xxxxxxxxxxxxxxx [mailto:linux-acpi-owner@xxxxxxxxxxxxxxx] On Behalf Of
> Borislav
> > Petkov
> > Subject: Re: 174cc7187e6f ACPICA: Tables: Back port acpi_get_table_with_size() and
> > early_acpi_os_unmap_memory() from Linux kernel
> >
> > On Sun, Jan 08, 2017 at 03:20:20AM +0100, Rafael J. Wysocki wrote:
> > >  drivers/iommu/amd_iommu_init.c |    2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > Index: linux-pm/drivers/iommu/amd_iommu_init.c
> > > ===================================================================
> > > --- linux-pm.orig/drivers/iommu/amd_iommu_init.c
> > > +++ linux-pm/drivers/iommu/amd_iommu_init.c
> > > @@ -2230,7 +2230,7 @@ static int __init early_amd_iommu_init(v
> > >  	 */
> > >  	ret = check_ivrs_checksum(ivrs_base);
> > >  	if (ret)
> > > -		return ret;
> > > +		goto out;
> > >
> > >  	amd_iommu_target_ivhd_type = get_highest_supported_ivhd_type(ivrs_base);
> > >  	DUMP_printk("Using IVHD type %#x\n", amd_iommu_target_ivhd_type);
> >
> > Good catch, this one needs to be applied regardless.
> >
> > However, it doesn't fix my issue though.
> >
> > But I think I have it - I went and applied the well-proven debugging
> > technique of sprinkling printks around. Here's what I'm seeing:
> >
> > early_amd_iommu_init()
> > |-> acpi_put_table(ivrs_base);
> > |-> acpi_tb_put_table(table_desc);
> > |-> acpi_tb_invalidate_table(table_desc);
> > |-> acpi_tb_release_table(...)
> > |-> acpi_os_unmap_memory
> > |-> acpi_os_unmap_iomem
> > |-> acpi_os_map_cleanup
> > |-> synchronize_rcu_expedited	<-- the kernel/rcu/tree_exp.h version with CONFIG_PREEMPT_RCU=y
> >
> > Now that function goes and sends IPIs, i.e., schedule_work()
> > but this is too early - we haven't even done workqueue_init().
> > Actually, from looking at the callstack, we do
> > kernel_init_freeable->native_smp_prepare_cpus() and workqueue_init()
> > comes next.
> >
> > And this makes sense because the splat rIP points to __queue_work() but
> > we haven't done that yet.
> >
> > So that acpi_put_table() is happening too early. Looks like AMD IOMMU
> > should not put the table but WTH do I know?!
> >
> > In any case, commenting out:
> >
> >         acpi_put_table(ivrs_base);
> >         ivrs_base = NULL;
> >
> > and the end of early_amd_iommu_init() makes the box boot again.
> 
> So please help to comment out these 2 lines (with descriptions and do not delete them).
> Until acpi_os_unmap_memory() is able to handle such an early case.

IMO, synchronize_rcu_expedited() should be improved:
If rcu_init() isn't called or there is nothing to synchronize, schedule_work() shouldn't be invoked.

Thanks and best regards
Lv

> 
> Thanks and best regards
> Lv
> 
> >
> > --
> > Regards/Gruss,
> >     Boris.
> >
> > Good mailing practices for 400: avoid top-posting and trim the reply.