dma-direct: refine dma_direct_alloc zone selection

We need to take the DMA offset and encryption bit into account when
selecting a zone.  User the opportunity to factor out the zone
selection into a helper for reuse.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

kernel/dma/direct.c

@@ -69,6 +69,22 @@ u64 dma_direct_get_required_mask(struct device *dev)
 	return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
 }
 
+static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask,
+		u64 *phys_mask)
+{
+	if (force_dma_unencrypted())
+		*phys_mask = __dma_to_phys(dev, dma_mask);
+	else
+		*phys_mask = dma_to_phys(dev, dma_mask);
+
+	/* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
+	if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
+		return GFP_DMA;
+	if (*phys_mask <= DMA_BIT_MASK(32))
+		return GFP_DMA32;
+	return 0;
+}
+
 static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
 {
 	return phys_to_dma_direct(dev, phys) + size - 1 <=
@@ -81,17 +97,13 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 	unsigned int count = PAGE_ALIGN(size) >> PAGE_SHIFT;
 	int page_order = get_order(size);
 	struct page *page = NULL;
+	u64 phys_mask;
 	void *ret;
 
 	/* we always manually zero the memory once we are done: */
 	gfp &= ~__GFP_ZERO;
-
-	/* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */
-	if (dev->coherent_dma_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))
-		gfp |= GFP_DMA;
-	if (dev->coherent_dma_mask <= DMA_BIT_MASK(32) && !(gfp & GFP_DMA))
-		gfp |= GFP_DMA32;
-
+	gfp |= __dma_direct_optimal_gfp_mask(dev, dev->coherent_dma_mask,
+			&phys_mask);
 again:
 	/* CMA can be used only in the context which permits sleeping */
 	if (gfpflags_allow_blocking(gfp)) {
@@ -110,15 +122,14 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 		page = NULL;
 
 		if (IS_ENABLED(CONFIG_ZONE_DMA32) &&
-		    dev->coherent_dma_mask < DMA_BIT_MASK(64) &&
+		    phys_mask < DMA_BIT_MASK(64) &&
 		    !(gfp & (GFP_DMA32 | GFP_DMA))) {
 			gfp |= GFP_DMA32;
 			goto again;
 		}
 
 		if (IS_ENABLED(CONFIG_ZONE_DMA) &&
-		    dev->coherent_dma_mask < DMA_BIT_MASK(32) &&
-		    !(gfp & GFP_DMA)) {
+		    phys_mask < DMA_BIT_MASK(32) && !(gfp & GFP_DMA)) {
 			gfp = (gfp & ~GFP_DMA32) | GFP_DMA;
 			goto again;
 		}