Re: [PATCH v8 15/23] dma-direct: pass attrs to dma_capable() for DMA_ATTR_CC_SHARED checks

Mostafa Saleh [off-list ref] writes:

quoted

 static inline bool dma_capable(struct device *dev, dma_addr_t addr, size_t size,
-		bool is_ram)
+		bool is_ram, unsigned long attrs)
 {
 	dma_addr_t end = addr + size - 1;
 
 	if (addr == DMA_MAPPING_ERROR)
 		return false;
+	/*
+	 * The DMA address was derived from encrypted RAM, but this device
+	 * requires unencrypted DMA addresses. Treat it as not DMA-capable
+	 * so the caller can fall back to a suitable SWIOTLB pool.
+	 */
+	if (!(attrs & DMA_ATTR_CC_SHARED) && force_dma_unencrypted(dev))
+		return false;
+

I guess it does not make sense to check the other way? I'd be worried if
some a confidential device uses shared memory which might leak info.

From the perspective of the dma_capable() check, this should be allowed;
that is, a trusted device is permitted to access shared memory.

-aneesh