remoteproc: qcom_q6v5_mss: map/unmap metadata region before/after use

The application processor accessing the dynamically assigned metadata
region after assigning it to the remote Q6 would lead to an XPU violation.
Fix this by un-mapping the metadata region post firmware header copy. The
metadata region is freed only after the modem Q6 is done with fw header
authentication.
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/1652248625-990-1-git-send-email-quic_sibis@quicinc.com

drivers/remoteproc/qcom_q6v5_mss.c

@@ -10,6 +10,7 @@
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/devcoredump.h>
+#include <linux/dma-map-ops.h>
 #include <linux/dma-mapping.h>
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
@@ -932,27 +933,52 @@ static void q6v5proc_halt_axi_port(struct q6v5 *qproc,
 static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
 				const char *fw_name)
 {
-	unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS;
+	unsigned long dma_attrs = DMA_ATTR_FORCE_CONTIGUOUS | DMA_ATTR_NO_KERNEL_MAPPING;
+	unsigned long flags = VM_DMA_COHERENT | VM_FLUSH_RESET_PERMS;
+	struct page **pages;
+	struct page *page;
 	dma_addr_t phys;
 	void *metadata;
 	int mdata_perm;
 	int xferop_ret;
 	size_t size;
-	void *ptr;
+	void *vaddr;
+	int count;
 	int ret;
+	int i;
 
 	metadata = qcom_mdt_read_metadata(fw, &size, fw_name, qproc->dev);
 	if (IS_ERR(metadata))
 		return PTR_ERR(metadata);
 
-	ptr = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
-	if (!ptr) {
+	page = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
+	if (!page) {
 		kfree(metadata);
 		dev_err(qproc->dev, "failed to allocate mdt buffer\n");
 		return -ENOMEM;
 	}
 
-	memcpy(ptr, metadata, size);
+	count = PAGE_ALIGN(size) >> PAGE_SHIFT;
+	pages = kmalloc_array(count, sizeof(struct page *), GFP_KERNEL);
+	if (!pages) {
+		ret = -ENOMEM;
+		goto free_dma_attrs;
+	}
+
+	for (i = 0; i < count; i++)
+		pages[i] = nth_page(page, i);
+
+	vaddr = vmap(pages, count, flags, pgprot_dmacoherent(PAGE_KERNEL));
+	kfree(pages);
+	if (!vaddr) {
+		dev_err(qproc->dev, "unable to map memory region: %pa+%zx\n", &phys, size);
+		ret = -EBUSY;
+		goto free_dma_attrs;
+	}
+
+	memcpy(vaddr, metadata, size);
+
+	vunmap(vaddr);
 
 	/* Hypervisor mapping to access metadata by modem */
 	mdata_perm = BIT(QCOM_SCM_VMID_HLOS);
@@ -982,7 +1008,7 @@ static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
 			 "mdt buffer not reclaimed system may become unstable\n");
 
 free_dma_attrs:
-	dma_free_attrs(qproc->dev, size, ptr, phys, dma_attrs);
+	dma_free_attrs(qproc->dev, size, page, phys, dma_attrs);
 	kfree(metadata);
 
 	return ret < 0 ? ret : 0;