s390/mem_detect: limit memory detection loop to "mem=" parameter

The current memory detection loop will detect all present memory of
a machine. This is true even if the user specified the "mem=" parameter
on the kernel command line.
This can be a problem since the memory detection may cause a fully
populated host page table for the guest, even for those parts of the
memory that the guest will never use afterwards.

So fix this and only detect memory up to a user supplied "mem=" limit
if specified.

Reported-by: Michael Johanssen <johanssn@de.ibm.com>
Reviewed-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/mm/mem_detect.c

@@ -12,7 +12,7 @@
 
 #define ADDR2G (1ULL << 31)
 
-static void find_memory_chunks(struct mem_chunk chunk[])
+static void find_memory_chunks(struct mem_chunk chunk[], unsigned long maxsize)
 {
 	unsigned long long memsize, rnmax, rzm;
 	unsigned long addr = 0, size;
@@ -27,6 +27,8 @@ static void find_memory_chunks(struct mem_chunk chunk[])
 		rzm = min(ADDR2G, rzm);
 		memsize = memsize ? min(ADDR2G, memsize) : ADDR2G;
 	}
+	if (maxsize)
+		memsize = memsize ? min((unsigned long)memsize, maxsize) : maxsize;
 	do {
 		size = 0;
 		type = tprot(addr);
@@ -36,6 +38,8 @@ static void find_memory_chunks(struct mem_chunk chunk[])
 				break;
 		} while (type == tprot(addr + size));
 		if (type == CHUNK_READ_WRITE || type == CHUNK_READ_ONLY) {
+			if (memsize && (addr + size > memsize))
+				size = memsize - addr;
 			chunk[i].addr = addr;
 			chunk[i].size = size;
 			chunk[i].type = type;
@@ -45,7 +49,20 @@ static void find_memory_chunks(struct mem_chunk chunk[])
 	} while (addr < memsize && i < MEMORY_CHUNKS);
 }
 
-void detect_memory_layout(struct mem_chunk chunk[])
+/**
+ * detect_memory_layout - fill mem_chunk array with memory layout data
+ * @chunk: mem_chunk array to be filled
+ * @maxsize: maximum address where memory detection should stop
+ *
+ * Fills the passed in memory chunk array with the memory layout of the
+ * machine. The array must have a size of at least MEMORY_CHUNKS and will
+ * be fully initialized afterwards.
+ * If the maxsize paramater has a value > 0 memory detection will stop at
+ * that address. It is guaranteed that all chunks have an ending address
+ * that is smaller than maxsize.
+ * If maxsize is 0 all memory will be detected.
+ */
+void detect_memory_layout(struct mem_chunk chunk[], unsigned long maxsize)
 {
 	unsigned long flags, flags_dat, cr0;
 
@@ -69,7 +86,7 @@ void detect_memory_layout(struct mem_chunk chunk[])
 	}
 	__ctl_store(cr0, 0, 0);
 	__ctl_clear_bit(0, 28);
-	find_memory_chunks(chunk);
+	find_memory_chunks(chunk, maxsize);
 	__ctl_load(cr0, 0, 0);
 out:
 	__arch_local_irq_ssm(flags_dat);