linux-user: implement mlock2(2) syscall

[PATCH v2] linux-user: implement mlock2(2) syscall

Posted by Michael Morrell 1 week, 4 days ago

TARGET_NR_mlock2 is defined for every target's syscall table (it has
been available on all Linux architectures since it was added in
kernel 4.4), and linux-user/strace.list already has an entry for it,
but linux-user/syscall.c has no case handler for it. A guest mlock2()
call therefore falls through to the default case and gets -ENOSYS
instead of being emulated, on every target.

mlock2() differs from mlock() only by a third `flags` argument
(MLOCK_ONFAULT). Add TARGET_MLOCK_ONFAULT and a case that validates
the flags argument and forwards to the host mlock2(), mirroring the
existing TARGET_NR_mlock case immediately above it.

Signed-off-by: Michael Morrell <mmorrell@tachyum.com>
---
 linux-user/syscall.c      | 9 +++++++++
 linux-user/syscall_defs.h | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index cfa68dfbdb..9f454502cb 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -11230,6 +11230,15 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
     case TARGET_NR_mlock:
         return get_errno(mlock(g2h(cpu, arg1), arg2));
 #endif
+#ifdef TARGET_NR_mlock2
+    case TARGET_NR_mlock2:
+        if (arg3 & ~TARGET_MLOCK_ONFAULT) {
+            return -TARGET_EINVAL;
+        }
+        return get_errno(mlock2(g2h(cpu, arg1), arg2,
+                                 (arg3 & TARGET_MLOCK_ONFAULT) ?
+                                 MLOCK_ONFAULT : 0));
+#endif
 #ifdef TARGET_NR_munlock
     case TARGET_NR_munlock:
         return get_errno(munlock(g2h(cpu, arg1), arg2));
diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h
index e28853c93b..f5831a6bad 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -2795,6 +2795,10 @@ struct target_mount_attr_ver0 {
 #ifndef RESOLVE_IN_ROOT
 #define RESOLVE_IN_ROOT         0x10
 #endif
+
+/* flags for mlock2() */
+#define TARGET_MLOCK_ONFAULT    0x01
+
 #if (defined(TARGET_I386) && defined(TARGET_ABI32)) || \
     (defined(TARGET_ARM) && defined(TARGET_ABI32)) || \
     defined(TARGET_M68K) || defined(TARGET_MICROBLAZE) || \
-- 
2.43.0

RE: [PATCH v2] linux-user: implement mlock2(2) syscall

Posted by Michael Morrell 4 days ago

ping

-----Original Message-----
From: Michael Morrell <mmorrell@tachyum.com> 
Sent: Monday, September 14, 2026 4:32 PM
To: qemu-devel@nongnu.org
Cc: Laurent Vivier <laurent@vivier.eu>; Helge Deller <deller@gmx.de>; Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>; Michael Morrell <mmorrell@tachyum.com>
Subject: [PATCH v2] linux-user: implement mlock2(2) syscall

TARGET_NR_mlock2 is defined for every target's syscall table (it has been available on all Linux architectures since it was added in kernel 4.4), and linux-user/strace.list already has an entry for it, but linux-user/syscall.c has no case handler for it. A guest mlock2() call therefore falls through to the default case and gets -ENOSYS instead of being emulated, on every target.

mlock2() differs from mlock() only by a third `flags` argument (MLOCK_ONFAULT). Add TARGET_MLOCK_ONFAULT and a case that validates the flags argument and forwards to the host mlock2(), mirroring the existing TARGET_NR_mlock case immediately above it.

Signed-off-by: Michael Morrell <mmorrell@tachyum.com>
---
 linux-user/syscall.c      | 9 +++++++++
 linux-user/syscall_defs.h | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c index cfa68dfbdb..9f454502cb 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -11230,6 +11230,15 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
     case TARGET_NR_mlock:
         return get_errno(mlock(g2h(cpu, arg1), arg2));  #endif
+#ifdef TARGET_NR_mlock2
+    case TARGET_NR_mlock2:
+        if (arg3 & ~TARGET_MLOCK_ONFAULT) {
+            return -TARGET_EINVAL;
+        }
+        return get_errno(mlock2(g2h(cpu, arg1), arg2,
+                                 (arg3 & TARGET_MLOCK_ONFAULT) ?
+                                 MLOCK_ONFAULT : 0)); #endif
 #ifdef TARGET_NR_munlock
     case TARGET_NR_munlock:
         return get_errno(munlock(g2h(cpu, arg1), arg2)); diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h index e28853c93b..f5831a6bad 100644
--- a/linux-user/syscall_defs.h
+++ b/linux-user/syscall_defs.h
@@ -2795,6 +2795,10 @@ struct target_mount_attr_ver0 {  #ifndef RESOLVE_IN_ROOT
 #define RESOLVE_IN_ROOT         0x10
 #endif
+
+/* flags for mlock2() */
+#define TARGET_MLOCK_ONFAULT    0x01
+
 #if (defined(TARGET_I386) && defined(TARGET_ABI32)) || \
     (defined(TARGET_ARM) && defined(TARGET_ABI32)) || \
     defined(TARGET_M68K) || defined(TARGET_MICROBLAZE) || \
--
2.43.0

Re: [PATCH v2] linux-user: implement mlock2(2) syscall

Posted by Helge Deller 4 days ago

On 9/22/26 22:14, Michael Morrell wrote:
> ping

has been merged upstream already:
https://gitlab.com/qemu-project/qemu/-/commit/30fa3eb41f85e114765e8476dc9a32a890b2e78f

Helge


> -----Original Message-----
> From: Michael Morrell <mmorrell@tachyum.com>
> Sent: Monday, September 14, 2026 4:32 PM
> To: qemu-devel@nongnu.org
> Cc: Laurent Vivier <laurent@vivier.eu>; Helge Deller <deller@gmx.de>; Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>; Michael Morrell <mmorrell@tachyum.com>
> Subject: [PATCH v2] linux-user: implement mlock2(2) syscall
> 
> TARGET_NR_mlock2 is defined for every target's syscall table (it has been available on all Linux architectures since it was added in kernel 4.4), and linux-user/strace.list already has an entry for it, but linux-user/syscall.c has no case handler for it. A guest mlock2() call therefore falls through to the default case and gets -ENOSYS instead of being emulated, on every target.
> 
> mlock2() differs from mlock() only by a third `flags` argument (MLOCK_ONFAULT). Add TARGET_MLOCK_ONFAULT and a case that validates the flags argument and forwards to the host mlock2(), mirroring the existing TARGET_NR_mlock case immediately above it.
> 
> Signed-off-by: Michael Morrell <mmorrell@tachyum.com>
> ---
>   linux-user/syscall.c      | 9 +++++++++
>   linux-user/syscall_defs.h | 4 ++++
>   2 files changed, 13 insertions(+)
> 
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c index cfa68dfbdb..9f454502cb 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -11230,6 +11230,15 @@ static abi_long do_syscall1(CPUArchState *cpu_env, int num, abi_long arg1,
>       case TARGET_NR_mlock:
>           return get_errno(mlock(g2h(cpu, arg1), arg2));  #endif
> +#ifdef TARGET_NR_mlock2
> +    case TARGET_NR_mlock2:
> +        if (arg3 & ~TARGET_MLOCK_ONFAULT) {
> +            return -TARGET_EINVAL;
> +        }
> +        return get_errno(mlock2(g2h(cpu, arg1), arg2,
> +                                 (arg3 & TARGET_MLOCK_ONFAULT) ?
> +                                 MLOCK_ONFAULT : 0)); #endif
>   #ifdef TARGET_NR_munlock
>       case TARGET_NR_munlock:
>           return get_errno(munlock(g2h(cpu, arg1), arg2)); diff --git a/linux-user/syscall_defs.h b/linux-user/syscall_defs.h index e28853c93b..f5831a6bad 100644
> --- a/linux-user/syscall_defs.h
> +++ b/linux-user/syscall_defs.h
> @@ -2795,6 +2795,10 @@ struct target_mount_attr_ver0 {  #ifndef RESOLVE_IN_ROOT
>   #define RESOLVE_IN_ROOT         0x10
>   #endif
> +
> +/* flags for mlock2() */
> +#define TARGET_MLOCK_ONFAULT    0x01
> +
>   #if (defined(TARGET_I386) && defined(TARGET_ABI32)) || \
>       (defined(TARGET_ARM) && defined(TARGET_ABI32)) || \
>       defined(TARGET_M68K) || defined(TARGET_MICROBLAZE) || \
> --
> 2.43.0
> 
> 
>