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[PATCH v4 02/23] linux-user: Introduce PAGE_ANON

From: Richard Henderson
Subject: [PATCH v4 02/23] linux-user: Introduce PAGE_ANON
Date: Thu, 28 Jan 2021 12:41:20 -1000

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.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
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 99a09ee137..c23c77589b 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -275,6 +275,8 @@ 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 c693505b60..7fb4c628e1 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 
+    if (flags & MAP_ANONYMOUS) {
+        page_flags |= PAGE_ANON;
+    }
     page_flags |= PAGE_RESET;
     page_set_flags(start, start + len, page_flags);

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