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

[Borislav Petkov]

+ Paul for comment.

Leaving in the rest for him.

On Mon, Jan 09, 2017 at 02:36:33AM +0000, Zheng, Lv wrote:
> 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.

-- 
Regards/Gruss,
    Boris.

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