[PATCH v2 02/17] linux-user: Introduce PAGE_ANON

[Richard Henderson]

Record whether the backing page is anonymous, or if it has file
backing.  This will allow us to get close to the Linux AArch64
ABI for MTE, which allows tag memory only on ram-backed VMAs.

The real ABI allows tag memory on files, when those files are
on ram-backed filesystems, such as tmpfs.  We will not be able
to implement that in QEMU linux-user.

Thankfully, anonymous memory for malloc arenas is the primary
consumer of this feature, so this restricted version should
still be of use.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
---
 include/exec/cpu-all.h | 2 ++
 linux-user/mmap.c      | 3 +++
 2 files changed, 5 insertions(+)

diff --git a/include/exec/cpu-all.h b/include/exec/cpu-all.h
index e5f564fa1f..3cac7750e4 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -277,6 +277,8 @@ extern intptr_t qemu_host_page_mask;
 #define PAGE_WRITE_INV 0x0020
 /* For use with page_set_flags: page is being replaced; target_data cleared. */
 #define PAGE_RESET     0x0040
+/* For linux-user, indicates that the page is MAP_ANON. */
+#define PAGE_ANON      0x0080
 
 #if defined(CONFIG_BSD) && defined(CONFIG_USER_ONLY)
 /* FIXME: Code that sets/uses this is broken and needs to go away.  */
diff --git a/linux-user/mmap.c b/linux-user/mmap.c
index f9832609b0..fdd55986a1 100644
--- a/linux-user/mmap.c
+++ b/linux-user/mmap.c
@@ -599,6 +599,9 @@ abi_long target_mmap(abi_ulong start, abi_ulong len, int 
target_prot,
         }
     }
  the_end1:
+    if (flags & MAP_ANONYMOUS) {
+        page_flags |= PAGE_ANON;
+    }
     page_flags |= PAGE_RESET;
     page_set_flags(start, start + len, page_flags);
  the_end:
-- 
2.25.1