mm: ioremap: Add ioremap/iounmap_allowed()

Add special hook for architecture to verify addr, size or prot
when ioremap() or iounmap(), which will make the generic ioremap
more useful.

  ioremap_allowed() return a bool,
    - true means continue to remap
    - false means skip remap and return directly
  iounmap_allowed() return a bool,
    - true means continue to vunmap
    - false code means skip vunmap and return directly

Meanwhile, only vunmap the address when it is in vmalloc area
as the generic ioremap only returns vmalloc addresses.

Acked-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Baoquan He <bhe@redhat.com>
Link: https://lore.kernel.org/r/20220607125027.44946-5-wangkefeng.wang@huawei.com
Signed-off-by: Will Deacon <will@kernel.org>

include/asm-generic/io.h

@@ -964,6 +964,32 @@ static inline void iounmap(volatile void __iomem *addr)
 #elif defined(CONFIG_GENERIC_IOREMAP)
 #include <linux/pgtable.h>
 
+/*
+ * Arch code can implement the following two hooks when using GENERIC_IOREMAP
+ * ioremap_allowed() return a bool,
+ *   - true means continue to remap
+ *   - false means skip remap and return directly
+ * iounmap_allowed() return a bool,
+ *   - true means continue to vunmap
+ *   - false means skip vunmap and return directly
+ */
+#ifndef ioremap_allowed
+#define ioremap_allowed ioremap_allowed
+static inline bool ioremap_allowed(phys_addr_t phys_addr, size_t size,
+				   unsigned long prot)
+{
+	return true;
+}
+#endif
+
+#ifndef iounmap_allowed
+#define iounmap_allowed iounmap_allowed
+static inline bool iounmap_allowed(void *addr)
+{
+	return true;
+}
+#endif
+
 void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size,
 			   unsigned long prot);
 void iounmap(volatile void __iomem *addr);

mm/ioremap.c

@@ -28,6 +28,9 @@ void __iomem *ioremap_prot(phys_addr_t phys_addr, size_t size,
 	phys_addr -= offset;
 	size = PAGE_ALIGN(size + offset);
 
+	if (!ioremap_allowed(phys_addr, size, prot))
+		return NULL;
+
 	area = get_vm_area_caller(size, VM_IOREMAP,
 			__builtin_return_address(0));
 	if (!area)
@@ -47,6 +50,12 @@ EXPORT_SYMBOL(ioremap_prot);
 
 void iounmap(volatile void __iomem *addr)
 {
-	vunmap((void *)((unsigned long)addr & PAGE_MASK));
+	void *vaddr = (void *)((unsigned long)addr & PAGE_MASK);
+
+	if (!iounmap_allowed(vaddr))
+		return;
+
+	if (is_vmalloc_addr(vaddr))
+		vunmap(vaddr);
 }
 EXPORT_SYMBOL(iounmap);