[RFC PATCH v2 4/5] softmmu/physmem: Introduce flatview_access_allowed() to check bus perms

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

Introduce flatview_access_allowed() to check bus permission
before running any bus transaction. For now this is a simple
stub.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 softmmu/physmem.c | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/softmmu/physmem.c b/softmmu/physmem.c
index e534dc69918..0d31a2f4199 100644
--- a/softmmu/physmem.c
+++ b/softmmu/physmem.c
@@ -2754,6 +2754,27 @@ static bool prepare_mmio_access(MemoryRegion *mr)
     return release_lock;
 }
 
+/**
+ * flatview_access_allowed
+ * @mr: #MemoryRegion to be accessed
+ * @attrs: memory transaction attributes
+ * @addr: address within that memory region
+ * @len: the number of bytes to access
+ * @result: optional pointer to a MemTxResult or NULL
+ *
+ * Check if a memory transaction is allowed. If an error occurs this
+ * method will return false to indicate denial, as well as setting
+ * @result to contain corresponding #MemTxResult.
+ *
+ * Returns: true if transaction is allowed, false if denied.
+ */
+static inline bool flatview_access_allowed(MemoryRegion *mr, MemTxAttrs attrs,
+                                           hwaddr addr, hwaddr len,
+                                           MemTxResult *result)
+{
+    return true;
+}
+
 /* Called within RCU critical section.  */
 static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
                                            MemTxAttrs attrs,
@@ -2768,7 +2789,9 @@ static MemTxResult flatview_write_continue(FlatView *fv, hwaddr addr,
     const uint8_t *buf = ptr;
 
     for (;;) {
-        if (!memory_access_is_direct(mr, true)) {
+        if (!flatview_access_allowed(mr, attrs, addr1, l, &result)) {
+            /* 'result' contains the error, keep going. */
+        } else if (!memory_access_is_direct(mr, true)) {
             release_lock |= prepare_mmio_access(mr);
             l = memory_access_size(mr, l, addr1);
             /* XXX: could force current_cpu to NULL to avoid
@@ -2810,9 +2833,13 @@ static MemTxResult flatview_write(FlatView *fv, hwaddr addr, MemTxAttrs attrs,
     hwaddr l;
     hwaddr addr1;
     MemoryRegion *mr;
+    MemTxResult result = MEMTX_OK;
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, true, attrs);
+    if (!flatview_access_allowed(mr, attrs, addr, len, &result)) {
+        return result;
+    }
     return flatview_write_continue(fv, addr, attrs, buf, len,
                                    addr1, l, mr);
 }
@@ -2831,7 +2858,9 @@ MemTxResult flatview_read_continue(FlatView *fv, hwaddr addr,
 
     fuzz_dma_read_cb(addr, len, mr);
     for (;;) {
-        if (!memory_access_is_direct(mr, false)) {
+        if (!flatview_access_allowed(mr, attrs, addr1, l, &result)) {
+            /* 'result' contains the error, keep going. */
+        } else if (!memory_access_is_direct(mr, false)) {
             /* I/O case */
             release_lock |= prepare_mmio_access(mr);
             l = memory_access_size(mr, l, addr1);
@@ -2871,9 +2900,13 @@ static MemTxResult flatview_read(FlatView *fv, hwaddr addr,
     hwaddr l;
     hwaddr addr1;
     MemoryRegion *mr;
+    MemTxResult result = MEMTX_OK;
 
     l = len;
     mr = flatview_translate(fv, addr, &addr1, &l, false, attrs);
+    if (!flatview_access_allowed(mr, attrs, addr, len, &result)) {
+        return result;
+    }
     return flatview_read_continue(fv, addr, attrs, buf, len,
                                   addr1, l, mr);
 }
-- 
2.31.1