The semaphore used by the AMD IOMMU to signal command
completion lived on the stack until now, which was safe as
the driver busy-waited on the semaphore with IRQs disabled,
so the stack can't go away under the driver.

But the recently introduced vmap-based stacks break this as
the physical address of the semaphore can't be determinded
easily anymore. The driver used the __pa() macro, but that
only works in the direct-mapping. The result were
Completion-Wait timeout errors seen by the IOMMU driver,
breaking system boot.

Since putting the semaphore on the stack is bad design
anyway, move the semaphore into 'struct amd_iommu'. It is
protected by the per-iommu lock and now in the direct
mapping again. This fixes the Completion-Wait timeout errors
and makes AMD IOMMU systems boot again with vmap-based
stacks enabled.
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>