From: Richard Henderson <richard.henderson@linaro.org>

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>
Message-id: 20210212184902.1251044-3-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@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 6421892830c..aedf5345449 100644
--- a/include/exec/cpu-all.h
+++ b/include/exec/cpu-all.h
@@ -267,6 +267,8 @@ 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 ac0624f31ac..c52b60482e1 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:
-- 
2.20.1

Hi,

Le 16/02/2021 à 17:16, Peter Maydell a écrit :
> From: Richard Henderson <richard.henderson@linaro.org>
> 
> 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>
> Message-id: 20210212184902.1251044-3-richard.henderson@linaro.org
> Signed-off-by: Peter Maydell <peter.maydell@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 6421892830c..aedf5345449 100644
> --- a/include/exec/cpu-all.h
> +++ b/include/exec/cpu-all.h
> @@ -267,6 +267,8 @@ 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 ac0624f31ac..c52b60482e1 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:
> 

Richard,

the new flag seems to break something.

See https://bugs.launchpad.net/qemu/+bug/1922617

Thanks,
Laurent