iommu/vt-d: Fix __domain_mapping()'s usage of switch_to_super_page()

switch_to_super_page() assumes the memory range it's working on is aligned
to the target large page level. Unfortunately, __domain_mapping() doesn't
take this into account when using it, and will pass unaligned ranges
ultimately freeing a PTE range larger than expected.

Take for example a mapping with the following iov_pfn range [0x3fe400,
0x4c0600), which should be backed by the following mappings:

iov_pfn [0x3fe400, 0x3fffff] covered by 2MiB pages
iov_pfn [0x400000, 0x4bffff] covered by 1GiB pages
iov_pfn [0x4c0000, 0x4c05ff] covered by 2MiB pages

Under this circumstance, __domain_mapping() will pass [0x400000, 0x4c05ff]
to switch_to_super_page() at a 1 GiB granularity, which will in turn
free PTEs all the way to iov_pfn 0x4fffff.

Mitigate this by rounding down the iov_pfn range passed to
switch_to_super_page() in __domain_mapping()
to the target large page level.

Additionally add range alignment checks to switch_to_super_page.

Fixes: 9906b9352a35 ("iommu/vt-d: Avoid duplicate removing in __domain_mapping()")
Signed-off-by: Eugene Koira <[e-mail]>
Cc: [e-mail]
Reviewed-by: Nicolas Saenz Julienne <[e-mail]>
Reviewed-by: David Woodhouse <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lu Baolu <[e-mail]>
Signed-off-by: Joerg Roedel <[e-mail]>

drivers/iommu/intel/iommu.c

···
 	unsigned long lvl_pages = lvl_to_nr_pages(level);
 	struct dma_pte *pte = NULL;
 
+	if (WARN_ON(!IS_ALIGNED(start_pfn, lvl_pages) ||
+		    !IS_ALIGNED(end_pfn + 1, lvl_pages)))
+		return;
+
 	while (start_pfn <= end_pfn) {
 		if (!pte)
 			pte = pfn_to_dma_pte(domain, start_pfn, &level,
···
 				unsigned long pages_to_remove;
 
 				pteval |= DMA_PTE_LARGE_PAGE;
-				pages_to_remove = min_t(unsigned long, nr_pages,
+				pages_to_remove = min_t(unsigned long,
+							round_down(nr_pages, lvl_pages),
 							nr_pte_to_next_page(pte) * lvl_pages);
 				end_pfn = iov_pfn + pages_to_remove - 1;
 				switch_to_super_page(domain, iov_pfn, end_pfn, largepage_lvl);