powerpc/vfio/iommu/kvm: Do not pin device memory

This new memory does not have page structs as it is not plugged to
the host so gup() will fail anyway.

This adds 2 helpers:
- mm_iommu_newdev() to preregister the "memory device" memory so
the rest of API can still be used;
- mm_iommu_is_devmem() to know if the physical address is one of thise
new regions which we must avoid unpinning of.

This adds @mm to tce_page_is_contained() and iommu_tce_xchg() to test
if the memory is device memory to avoid pfn_to_page().

This adds a check for device memory in mm_iommu_ua_mark_dirty_rm() which
does delayed pages dirtying.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/iommu.c

@@ -47,6 +47,7 @@
 #include <asm/fadump.h>
 #include <asm/vio.h>
 #include <asm/tce.h>
+#include <asm/mmu_context.h>
 
 #define DBG(...)
 
@@ -993,15 +994,19 @@ int iommu_tce_check_gpa(unsigned long page_shift, unsigned long gpa)
 }
 EXPORT_SYMBOL_GPL(iommu_tce_check_gpa);
 
-long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
-		unsigned long *hpa, enum dma_data_direction *direction)
+long iommu_tce_xchg(struct mm_struct *mm, struct iommu_table *tbl,
+		unsigned long entry, unsigned long *hpa,
+		enum dma_data_direction *direction)
 {
 	long ret;
+	unsigned long size = 0;
 
 	ret = tbl->it_ops->exchange(tbl, entry, hpa, direction);
 
 	if (!ret && ((*direction == DMA_FROM_DEVICE) ||
-			(*direction == DMA_BIDIRECTIONAL)))
+			(*direction == DMA_BIDIRECTIONAL)) &&
+			!mm_iommu_is_devmem(mm, *hpa, tbl->it_page_shift,
+					&size))
 		SetPageDirty(pfn_to_page(*hpa >> PAGE_SHIFT));
 
 	/* if (unlikely(ret))