drivers: remoteproc: ti_k3_m4: use memremap for no-map reserved memory

Replace devm_ioremap_wc() with memremap(MEMREMAP_WB) for no-map
reserved-memory regions that have struct page backing.

Using ioremap_wc() on a region backed by struct pages violates
ARM64 memory aliasing rules by creating conflicting cached and
write-combining mappings of the same physical pages. This can
cause SIGBUS faults in unrelated userspace processes.

Add a devm cleanup action to call memunmap() on the mapped
region when the device is released.

Signed-off-by: Heinrich Toews <ht@twx-software.de>

drivers/remoteproc/ti_k3_m4_remoteproc.c

@@ -525,6 +525,12 @@ static void k3_m4_rproc_dev_mem_release(void *data)
 	of_reserved_mem_device_release(dev);
 }
 
+
+static void k3_m4_rproc_rmem_release(void *data)
+{
+	memunmap(data);
+}
+
 static int k3_m4_reserved_mem_init(struct k3_m4_rproc *kproc)
 {
 	struct device *dev = kproc->dev;
@@ -580,12 +586,23 @@ static int k3_m4_reserved_mem_init(struct k3_m4_rproc *kproc)
 		/* 64-bit address regions currently not supported */
 		kproc->rmem[i].dev_addr = (u32)rmem->base;
 		kproc->rmem[i].size = rmem->size;
-		kproc->rmem[i].cpu_addr = devm_ioremap_wc(dev, rmem->base, rmem->size);
+		/*
+		 * Use memremap(MEMREMAP_WB) instead of ioremap_wc() for no-map
+		 * reserved-memory regions that have struct page backing.
+		 * ioremap_wc() on a region with struct page violates ARM64 memory
+		 * aliasing rules (cached vs. WC mapping of the same physical page)
+		 * and causes SIGBUS in unrelated userspace processes.
+		 */
+		kproc->rmem[i].cpu_addr = (__force void __iomem *)memremap(rmem->base, rmem->size, MEMREMAP_WB);
 		if (!kproc->rmem[i].cpu_addr) {
 			dev_err(dev, "failed to map reserved memory#%d at %pa of size %pa\n",
 				i + 1, &rmem->base, &rmem->size);
 			return -ENOMEM;
 		}
+		ret = devm_add_action_or_reset(dev, k3_m4_rproc_rmem_release,
+					       (__force void *)kproc->rmem[i].cpu_addr);
+		if (ret)
+			return ret;
 
 		dev_dbg(dev, "reserved memory%d: bus addr %pa size 0x%zx va %pK da 0x%x\n",
 			i + 1, &kproc->rmem[i].bus_addr,