make gnttab_dma_map_page() compound page aware

While this was found to be a problem in practice only on recent
kernels, it was nevertheless a mistake from the beginning to not take
into consideration compound pages.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/arch/i386/kernel/pci-dma-xen.c
+++ b/arch/i386/kernel/pci-dma-xen.c
@@ -120,7 +120,7 @@ dma_map_sg(struct device *hwdev, struct 
 		for (i = 0; i < nents; i++ ) {
 			BUG_ON(!sg[i].page);
 			sg[i].dma_address =
-				gnttab_dma_map_page(sg[i].page) + sg[i].offset;
+				gnttab_dma_map_page(sg[i].page, sg[i].offset);
 			sg[i].dma_length  = sg[i].length;
 			IOMMU_BUG_ON(address_needs_mapping(
 				hwdev, sg[i].dma_address));
@@ -165,7 +165,7 @@ dma_map_page(struct device *dev, struct 
 		dma_addr = swiotlb_map_page(
 			dev, page, offset, size, direction);
 	} else {
-		dma_addr = gnttab_dma_map_page(page) + offset;
+		dma_addr = gnttab_dma_map_page(page, offset);
 		IOMMU_BUG_ON(address_needs_mapping(dev, dma_addr));
 	}
 
@@ -363,8 +363,8 @@ dma_map_single(struct device *dev, void 
 	if (swiotlb) {
 		dma = swiotlb_map_single(dev, ptr, size, direction);
 	} else {
-		dma = gnttab_dma_map_page(virt_to_page(ptr)) +
-		      offset_in_page(ptr);
+		dma = gnttab_dma_map_page(virt_to_page(ptr),
+					  offset_in_page(ptr));
 		IOMMU_BUG_ON(range_straddles_page_boundary(__pa(ptr), size));
 		IOMMU_BUG_ON(address_needs_mapping(dev, dma));
 	}
--- a/arch/ia64/hp/common/sba_iommu.c
+++ b/arch/ia64/hp/common/sba_iommu.c
@@ -1522,7 +1522,7 @@ dma_map_sg(struct device *hwdev, struct 
 		for (sg = sglist ; filled < nents ; filled++, sg++){
 			sg->dma_length = sg->length;
 #ifdef CONFIG_XEN
-			sg->dma_address = gnttab_dma_map_page(sg->page) + sg->offset;
+			sg->dma_address = gnttab_dma_map_page(sg->page, sg->offset);
 #else
 			sg->dma_address = virt_to_bus(sba_sg_address(sg));
 #endif
--- a/arch/ia64/xen/xen_dma.c
+++ b/arch/ia64/xen/xen_dma.c
@@ -92,7 +92,7 @@ dma_map_sg(struct device *hwdev, struct 
 	int i;
 
 	for (i = 0 ; i < nents ; i++) {
-		sg[i].dma_address = gnttab_dma_map_page(sg[i].page) + sg[i].offset;
+		sg[i].dma_address = gnttab_dma_map_page(sg[i].page, sg[i].offset);
 		sg[i].dma_length  = sg[i].length;
 
 		IOMMU_BUG_ON(address_needs_mapping(dev, sg[i].dma_address));
--- a/drivers/xen/core/gnttab.c
+++ b/drivers/xen/core/gnttab.c
@@ -705,6 +705,8 @@ void __gnttab_dma_map_page(struct page *
 	if (!is_running_on_xen() || !PageForeign(page))
 		return;
 
+	BUG_ON(PageCompound(page));
+
 	do {
 		seq = read_seqbegin(&gnttab_dma_lock);
 
--- a/include/asm-i386/mach-xen/asm/gnttab_dma.h
+++ b/include/asm-i386/mach-xen/asm/gnttab_dma.h
@@ -21,16 +21,24 @@
 #ifndef _ASM_I386_GNTTAB_DMA_H
 #define _ASM_I386_GNTTAB_DMA_H
 
+#include <asm/bug.h>
+
 static inline int gnttab_dma_local_pfn(struct page *page)
 {
 	/* Has it become a local MFN? */
 	return pfn_valid(mfn_to_local_pfn(pfn_to_mfn(page_to_pfn(page))));
 }
 
-static inline maddr_t gnttab_dma_map_page(struct page *page)
+static inline maddr_t gnttab_dma_map_page(struct page *page,
+					  unsigned long offset)
 {
+	unsigned int pgnr = offset >> PAGE_SHIFT;
+	unsigned int order = PageCompound(page) ? (long)page[1].lru.prev : 0;
+
+	BUG_ON(pgnr >> order);
 	__gnttab_dma_map_page(page);
-	return ((maddr_t)pfn_to_mfn(page_to_pfn(page)) << PAGE_SHIFT);
+	return ((maddr_t)pfn_to_mfn(page_to_pfn(page) + pgnr) << PAGE_SHIFT)
+	       + (offset & ~PAGE_MASK);
 }
 
 static inline void gnttab_dma_unmap_page(maddr_t maddr)
--- a/include/asm-ia64/gnttab_dma.h
+++ b/include/asm-ia64/gnttab_dma.h
@@ -21,6 +21,8 @@
 #ifndef _ASM_IA64_GNTTAB_DMA_H
 #define _ASM_IA64_GNTTAB_DMA_H
 
+#include <asm/bug.h>
+
 static inline int gnttab_dma_local_pfn(struct page *page)
 {
 	return 0;
@@ -32,10 +34,15 @@
 	__gnttab_dma_map_page(page);
 }
 
-static inline dma_addr_t gnttab_dma_map_page(struct page *page)
+static inline dma_addr_t gnttab_dma_map_page(struct page *page,
+					     unsigned long offset)
 {
+	unsigned int pgnr = offset >> PAGE_SHIFT;
+	unsigned int order = PageCompound(page) ? (long)page[1].lru.prev : 0;
+
+	BUG_ON(pgnr >> order);
 	gnttab_dma_use_page(page);
-	return page_to_bus(page);
+	return page_to_bus(page + pgnr) + (offset & ~PAGE_MASK);
 }
 
 static inline dma_addr_t gnttab_dma_map_virt(void *ptr)
--- a/lib/swiotlb-xen.c
+++ b/lib/swiotlb-xen.c
@@ -501,8 +501,8 @@ swiotlb_full(struct device *dev, size_t 
 dma_addr_t
 swiotlb_map_single(struct device *hwdev, void *ptr, size_t size, int dir)
 {
-	dma_addr_t dev_addr = gnttab_dma_map_page(virt_to_page(ptr)) +
-			      offset_in_page(ptr);
+	dma_addr_t dev_addr = gnttab_dma_map_page(virt_to_page(ptr),
+						  offset_in_page(ptr));
 	void *map;
 	struct phys_addr buffer;
 
@@ -613,7 +613,7 @@ swiotlb_map_sg(struct device *hwdev, str
 	BUG_ON(dir == DMA_NONE);
 
 	for (i = 0; i < nelems; i++, sg++) {
-		dev_addr = gnttab_dma_map_page(sg->page) + sg->offset;
+		dev_addr = gnttab_dma_map_page(sg->page, sg->offset);
 
 		if (range_straddles_page_boundary(page_to_pseudophys(sg->page)
 						  + sg->offset, sg->length)
@@ -705,7 +705,7 @@ swiotlb_map_page(struct device *hwdev, s
 	dma_addr_t dev_addr;
 	char *map;
 
-	dev_addr = gnttab_dma_map_page(page) + offset;
+	dev_addr = gnttab_dma_map_page(page, offset);
 	if (address_needs_mapping(hwdev, dev_addr)) {
 		gnttab_dma_unmap_page(dev_addr);
 		buffer.page   = page;