powerpc/mem: Remove address argument to flush_coherent_icache()

flush_coherent_icache() can use any valid address as mentionned
by the comment.

Use PAGE_OFFSET as base address. This allows removing the
user access stuff.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/742b6360ae4f344a1c6ecfadcf3b6645f443fa7a.1617895813.git.christophe.leroy@csgroup.eu

arch/powerpc/mm/cacheflush.c

@@ -5,10 +5,9 @@
 
 /**
  * flush_coherent_icache() - if a CPU has a coherent icache, flush it
- * @addr: The base address to use (can be any valid address, the whole cache will be flushed)
  * Return true if the cache was flushed, false otherwise
  */
-static inline bool flush_coherent_icache(unsigned long addr)
+static inline bool flush_coherent_icache(void)
 {
 	/*
 	 * For a snooping icache, we still need a dummy icbi to purge all the
@@ -18,9 +17,7 @@ static inline bool flush_coherent_icache(unsigned long addr)
 	 */
 	if (cpu_has_feature(CPU_FTR_COHERENT_ICACHE)) {
 		mb(); /* sync */
-		allow_read_from_user((const void __user *)addr, L1_CACHE_BYTES);
-		icbi((void *)addr);
-		prevent_read_from_user((const void __user *)addr, L1_CACHE_BYTES);
+		icbi((void *)PAGE_OFFSET);
 		mb(); /* sync */
 		isync();
 		return true;
@@ -60,7 +57,7 @@ static void invalidate_icache_range(unsigned long start, unsigned long stop)
  */
 void flush_icache_range(unsigned long start, unsigned long stop)
 {
-	if (flush_coherent_icache(start))
+	if (flush_coherent_icache())
 		return;
 
 	clean_dcache_range(start, stop);
@@ -146,7 +143,7 @@ static void __flush_dcache_icache(void *p)
 {
 	unsigned long addr = (unsigned long)p;
 
-	if (flush_coherent_icache(addr))
+	if (flush_coherent_icache())
 		return;
 
 	clean_dcache_range(addr, addr + PAGE_SIZE);
@@ -200,7 +197,7 @@ void flush_dcache_icache_page(struct page *page)
 	} else {
 		unsigned long addr = page_to_pfn(page) << PAGE_SHIFT;
 
-		if (flush_coherent_icache(addr))
+		if (flush_coherent_icache())
 			return;
 		flush_dcache_icache_phys(addr);
 	}