[RFC PATCH 10/12] exec/memattrs: Introduce MemTxAttrs::direct_access field

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

Add the 'direct_access' bit to the memory attributes to restrict
bus master access to ROM/RAM.
Have read/write accessors return MEMTX_BUS_ERROR if an access is
restricted and the region is not ROM/RAM ('direct').
Add corresponding trace events.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 include/exec/memattrs.h | 3 +++
 exec.c                  | 8 ++++++++
 trace-events            | 1 +
 3 files changed, 12 insertions(+)

diff --git a/include/exec/memattrs.h b/include/exec/memattrs.h
index 95f2d20d55b..c27cf639a96 100644
--- a/include/exec/memattrs.h
+++ b/include/exec/memattrs.h
@@ -35,6 +35,8 @@ typedef struct MemTxAttrs {
     unsigned int secure:1;
     /* Memory access is usermode (unprivileged) */
     unsigned int user:1;
+    /* Bus master restricted to ROM/RAM slaves */
+    unsigned int direct_access:1;
     /* Requester ID (for MSI for example) */
     unsigned int requester_id:16;
     /* Invert endianness for this page */
@@ -66,6 +68,7 @@ typedef struct MemTxAttrs {
 #define MEMTX_OK 0
 #define MEMTX_ERROR             (1U << 0) /* device returned an error */
 #define MEMTX_DECODE_ERROR      (1U << 1) /* nothing at that address */
+#define MEMTX_BUS_ERROR         (1U << 2) /* bus returned an error */
 typedef uint32_t MemTxResult;
 
 #endif
diff --git a/exec.c b/exec.c
index 7683afb6a8e..e6185eb04de 100644
--- a/exec.c
+++ b/exec.c
@@ -3213,6 +3213,10 @@ static MemTxResult flatview_write(FlatView *fv, hwaddr addr, MemTxAttrs attrs,
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, true, attrs);
+    if (attrs.direct_access && !memory_access_is_direct(mr, true)) {
+        trace_memory_access_illegal(true, addr, len, mr->name);
+        return MEMTX_BUS_ERROR;
+    }
     result = flatview_write_continue(fv, addr, attrs, buf, len,
                                      addr1, l, mr);
 
@@ -3275,6 +3279,10 @@ static MemTxResult flatview_read(FlatView *fv, hwaddr addr,
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, false, attrs);
+    if (attrs.direct_access && !memory_access_is_direct(mr, false)) {
+        trace_memory_access_illegal(false, addr, len, mr->name);
+        return MEMTX_BUS_ERROR;
+    }
     return flatview_read_continue(fv, addr, attrs, buf, len,
                                   addr1, l, mr);
 }
diff --git a/trace-events b/trace-events
index 42107ebc697..931896735b1 100644
--- a/trace-events
+++ b/trace-events
@@ -54,6 +54,7 @@ find_ram_offset_loop(uint64_t size, uint64_t candidate, uint64_t offset, uint64_
 ram_block_discard_range(const char *rbname, void *hva, size_t length, bool need_madvise, bool need_fallocate, int ret) "%s@%p + 0x%zx: madvise: %d fallocate: %d ret: %d"
 memory_notdirty_write_access(uint64_t vaddr, uint64_t ram_addr, unsigned size) "0x%" PRIx64 " ram_addr 0x%" PRIx64 " size %u"
 memory_notdirty_set_dirty(uint64_t vaddr) "0x%" PRIx64
+memory_access_illegal(bool is_write, uint64_t addr, uint64_t len, const char *mr_name) "is_write:%u addr:0x%08" PRIx64 " size:0x%04" PRIx64 " region:'%s'"
 
 # memory.c
 memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value, unsigned size) "cpu %d mr %p addr 0x%"PRIx64" value 0x%"PRIx64" size %u"
-- 
2.26.2