[PATCH v2] softmmu/physmem: Fix address of FlatView access in address_space_(read|write)_cached_slow()

[Alberto Faria <afaria@redhat.com>]

flatview_(read|write)_continue() must be called with an address in the
FlatView's address space, but `addr` is relative to the
MemoryRegionCache.

Convert `addr` from the MemoryRegionCache's address space to the
FlatView's before passing it to flatview_(read|write)_continue().

This problem was uncovered while attempting to perform unaligned writes,
which caused flatview_write_continue() to reach the call to
flatview_translate(), which then translated the erroneous address and
caused the subsequent write to fail.

Fixes: 48564041a7 ("exec: reintroduce MemoryRegion caching")
Co-Developed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Alberto Faria <afaria@redhat.com>
---
 softmmu/physmem.c | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index 50231bab30..bdde4eb927 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -3420,6 +3420,14 @@ static inline MemoryRegion *address_space_translate_cached(
     return section.mr;
 }
 
+/* Converts `addr` from the address space of `cache` to that of `cache->fv`. */
+static inline hwaddr addr_in_cache_to_in_flat_view(MemoryRegionCache *cache,
+                                                   hwaddr addr)
+{
+    hwaddr addr_in_mrs = addr + cache->xlat - cache->mrs.offset_within_region;
+    return addr_in_mrs + cache->mrs.offset_within_address_space;
+}
+
 /* Called from RCU critical section. address_space_read_cached uses this
  * out of line function when the target is an MMIO or IOMMU region.
  */
@@ -3434,8 +3442,9 @@ address_space_read_cached_slow(MemoryRegionCache *cache, hwaddr addr,
     mr = address_space_translate_cached(cache, addr, &addr1, &l, false,
                                         MEMTXATTRS_UNSPECIFIED);
     return flatview_read_continue(cache->fv,
-                                  addr, MEMTXATTRS_UNSPECIFIED, buf, len,
-                                  addr1, l, mr);
+                                  addr_in_cache_to_in_flat_view(cache, addr),
+                                  MEMTXATTRS_UNSPECIFIED, buf, len, addr1, l,
+                                  mr);
 }
 
 /* Called from RCU critical section. address_space_write_cached uses this
@@ -3452,8 +3461,9 @@ address_space_write_cached_slow(MemoryRegionCache *cache, hwaddr addr,
     mr = address_space_translate_cached(cache, addr, &addr1, &l, true,
                                         MEMTXATTRS_UNSPECIFIED);
     return flatview_write_continue(cache->fv,
-                                   addr, MEMTXATTRS_UNSPECIFIED, buf, len,
-                                   addr1, l, mr);
+                                   addr_in_cache_to_in_flat_view(cache, addr),
+                                   MEMTXATTRS_UNSPECIFIED, buf, len, addr1, l,
+                                   mr);
 }
 
 #define ARG1_DECL                MemoryRegionCache *cache
-- 
2.37.2