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[1/2] exec: Don't reuse unassigned_mem_ops for io_mem_rom

Message ID 1513187549-2435-2-git-send-email-peter.maydell@linaro.org
State Superseded
Headers show
Series Don't abort on writes to ROMs | expand

Commit Message

Peter Maydell Dec. 13, 2017, 5:52 p.m. UTC 
We set up the io_mem_rom special memory region using the
unassigned_mem_ops structure; this is then used when a guest tries to
write to ROM.  This is incorrect, because the behaviour of unassigned
memory may be different from that of ROM for writes.  In particular,
on some architectures writing to unassigned memory generates a guest
exception, whereas writing to ROM is generally ignored.  Use a
special readonly_mem_ops for this purpose instead, so writes to
ROM are ignored for all guest CPUs.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

---
 exec.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

-- 
2.7.4
diff mbox series

Patch

diff --git a/exec.c b/exec.c
index 03238a3..74b8727 100644
--- a/exec.c
+++ b/exec.c
@@ -2720,6 +2720,37 @@  static uint16_t dummy_section(PhysPageMap *map, FlatView *fv, MemoryRegion *mr)
     return phys_section_add(map, &section);
 }
 
+static void readonly_mem_write(void *opaque, hwaddr addr,
+                               uint64_t val, unsigned size)
+{
+    /* Ignore any write to ROM. */
+}
+
+static bool readonly_mem_accepts(void *opaque, hwaddr addr,
+                                 unsigned size, bool is_write)
+{
+    return is_write;
+}
+
+/* This will only be used for writes, because reads are special cased
+ * to directly access the underlying host ram.
+ */
+static const MemoryRegionOps readonly_mem_ops = {
+    .write = readonly_mem_write,
+    .valid.accepts = readonly_mem_accepts,
+    .endianness = DEVICE_NATIVE_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+        .unaligned = false,
+    },
+    .impl = {
+        .min_access_size = 1,
+        .max_access_size = 8,
+        .unaligned = false,
+    },
+};
+
 MemoryRegion *iotlb_to_region(CPUState *cpu, hwaddr index, MemTxAttrs attrs)
 {
     int asidx = cpu_asidx_from_attrs(cpu, attrs);
@@ -2732,7 +2763,8 @@  MemoryRegion *iotlb_to_region(CPUState *cpu, hwaddr index, MemTxAttrs attrs)
 
 static void io_mem_init(void)
 {
-    memory_region_init_io(&io_mem_rom, NULL, &unassigned_mem_ops, NULL, NULL, UINT64_MAX);
+    memory_region_init_io(&io_mem_rom, NULL, &readonly_mem_ops,
+                          NULL, NULL, UINT64_MAX);
     memory_region_init_io(&io_mem_unassigned, NULL, &unassigned_mem_ops, NULL,
                           NULL, UINT64_MAX);