powerpc/watchpoint: Fix quadword instruction handling on p10 predecessors

On p10 predecessors, watchpoint with quadword access is compared at
quadword length. If the watch range is doubleword or less than that
in a first half of quadword aligned 16 bytes, and if there is any
unaligned quadword access which will access only the 2nd half, the
handler should consider it as extraneous and emulate/single-step it
before continuing.

Fixes: 74c68810 ("powerpc/watchpoint: Prepare handler to handle more than one watchpoint")
Reported-by: Pedro Miraglia Franco de Carvalho <pedromfc@linux.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902042945.129369-2-ravi.bangoria@linux.ibm.com

arch/powerpc/include/asm/hw_breakpoint.h

@@ -42,6 +42,7 @@ struct arch_hw_breakpoint {
 #else
 #define HW_BREAKPOINT_SIZE  0x8
 #endif
+#define HW_BREAKPOINT_SIZE_QUADWORD	0x10
 
 #define DABR_MAX_LEN	8
 #define DAWR_MAX_LEN	512

arch/powerpc/kernel/hw_breakpoint.c

@@ -520,9 +520,17 @@ static bool ea_hw_range_overlaps(unsigned long ea, int size,
 				 struct arch_hw_breakpoint *info)
 {
 	unsigned long hw_start_addr, hw_end_addr;
+	unsigned long align_size = HW_BREAKPOINT_SIZE;
 
-	hw_start_addr = ALIGN_DOWN(info->address, HW_BREAKPOINT_SIZE);
-	hw_end_addr = ALIGN(info->address + info->len, HW_BREAKPOINT_SIZE);
+	/*
+	 * On p10 predecessors, quadword is handle differently then
+	 * other instructions.
+	 */
+	if (!cpu_has_feature(CPU_FTR_ARCH_31) && size == 16)
+		align_size = HW_BREAKPOINT_SIZE_QUADWORD;
+
+	hw_start_addr = ALIGN_DOWN(info->address, align_size);
+	hw_end_addr = ALIGN(info->address + info->len, align_size);
 
 	return ((ea < hw_end_addr) && (ea + size > hw_start_addr));
 }