dept needs to notice every entrance from user to kernel mode to treat
every kernel context independently when tracking wait-event dependencies.
Roughly, system call and user oriented fault are the cases.

Make dept aware of the entrances of x86_64 and add support
CONFIG_ARCH_HAS_DEPT_SUPPORT to x86_64.

Signed-off-by: Byungchul Park <byungchul@sk.com>
---
 arch/x86/Kconfig            | 1 +
 arch/x86/entry/syscall_64.c | 7 +++++++
 arch/x86/mm/fault.c         | 7 +++++++
 3 files changed, 15 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 05880301212e..46021cf5934b 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -38,6 +38,7 @@ config X86_64
 	select ZONE_DMA32
 	select EXECMEM if DYNAMIC_FTRACE
 	select ACPI_MRRM if ACPI
+	select ARCH_HAS_DEPT_SUPPORT
 
 config FORCE_DYNAMIC_FTRACE
 	def_bool y
diff --git a/arch/x86/entry/syscall_64.c b/arch/x86/entry/syscall_64.c
index b6e68ea98b83..66bd5af5aff1 100644
--- a/arch/x86/entry/syscall_64.c
+++ b/arch/x86/entry/syscall_64.c
@@ -8,6 +8,7 @@
 #include <linux/entry-common.h>
 #include <linux/nospec.h>
 #include <asm/syscall.h>
+#include <linux/dept.h>
 
 #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
 #define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
@@ -86,6 +87,12 @@ static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
 /* Returns true to return using SYSRET, or false to use IRET */
 __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
 {
+	/*
+	 * This is a system call from user mode.  Make dept work with a
+	 * new kernel mode context.
+	 */
+	dept_update_cxt();
+
 	add_random_kstack_offset();
 	nr = syscall_enter_from_user_mode(regs, nr);
 
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 998bd807fc7b..017edb75f0a0 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -19,6 +19,7 @@
 #include <linux/mm_types.h>
 #include <linux/mm.h>			/* find_and_lock_vma() */
 #include <linux/vmalloc.h>
+#include <linux/dept.h>
 
 #include <asm/cpufeature.h>		/* boot_cpu_has, ...		*/
 #include <asm/traps.h>			/* dotraplinkage, ...		*/
@@ -1219,6 +1220,12 @@ void do_user_addr_fault(struct pt_regs *regs,
 	tsk = current;
 	mm = tsk->mm;
 
+	/*
+	 * This fault comes from user mode.  Make dept work with a new
+	 * kernel mode context.
+	 */
+	dept_update_cxt();
+
 	if (unlikely((error_code & (X86_PF_USER | X86_PF_INSTR)) == X86_PF_INSTR)) {
 		/*
 		 * Whoops, this is kernel mode code trying to execute from
-- 
2.17.1

On 10/2/25 01:12, Byungchul Park wrote:
> dept needs to notice every entrance from user to kernel mode to treat
> every kernel context independently when tracking wait-event dependencies.
> Roughly, system call and user oriented fault are the cases.

"Roughly"?

>  #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
>  #define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
> @@ -86,6 +87,12 @@ static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
>  /* Returns true to return using SYSRET, or false to use IRET */
>  __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
>  {
> +	/*
> +	 * This is a system call from user mode.  Make dept work with a
> +	 * new kernel mode context.
> +	 */
> +	dept_update_cxt();
> +
>  	add_random_kstack_offset();
>  	nr = syscall_enter_from_user_mode(regs, nr);

Please take a look in syscall_enter_from_user_mode(). You'll see the
quite nicely-named function: enter_from_user_mode(). That might be a
nice place to put code that you want to run when the kernel is entered
from user mode.

> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 998bd807fc7b..017edb75f0a0 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -19,6 +19,7 @@
>  #include <linux/mm_types.h>
>  #include <linux/mm.h>			/* find_and_lock_vma() */
>  #include <linux/vmalloc.h>
> +#include <linux/dept.h>
>  
>  #include <asm/cpufeature.h>		/* boot_cpu_has, ...		*/
>  #include <asm/traps.h>			/* dotraplinkage, ...		*/
> @@ -1219,6 +1220,12 @@ void do_user_addr_fault(struct pt_regs *regs,
>  	tsk = current;
>  	mm = tsk->mm;
>  
> +	/*
> +	 * This fault comes from user mode.  Make dept work with a new
> +	 * kernel mode context.
> +	 */
> +	dept_update_cxt();
No, this fault does not come from user mode. That's why we call it "user
addr" fault, not "user mode" fault. You end up here if, for instance,
the kernel faults doing a copy_from_user().

On Thu, Oct 02, 2025 at 08:22:29AM -0700, Dave Hansen wrote:
> On 10/2/25 01:12, Byungchul Park wrote:
> > dept needs to notice every entrance from user to kernel mode to treat
> > every kernel context independently when tracking wait-event dependencies.
> > Roughly, system call and user oriented fault are the cases.
> 
> "Roughly"?

I will change it to a better one.

> >  #define __SYSCALL(nr, sym) extern long __x64_##sym(const struct pt_regs *);
> >  #define __SYSCALL_NORETURN(nr, sym) extern long __noreturn __x64_##sym(const struct pt_regs *);
> > @@ -86,6 +87,12 @@ static __always_inline bool do_syscall_x32(struct pt_regs *regs, int nr)
> >  /* Returns true to return using SYSRET, or false to use IRET */
> >  __visible noinstr bool do_syscall_64(struct pt_regs *regs, int nr)
> >  {
> > +     /*
> > +      * This is a system call from user mode.  Make dept work with a
> > +      * new kernel mode context.
> > +      */
> > +     dept_update_cxt();
> > +
> >       add_random_kstack_offset();
> >       nr = syscall_enter_from_user_mode(regs, nr);
> 
> Please take a look in syscall_enter_from_user_mode(). You'll see the
> quite nicely-named function: enter_from_user_mode(). That might be a
> nice place to put code that you want to run when the kernel is entered
> from user mode.

I wanted to put dept_update_cxt() to the very beginning of c code but..
yeah enter_from_user_mode() looks fine or even better.  Thanks a lot.

> > diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> > index 998bd807fc7b..017edb75f0a0 100644
> > --- a/arch/x86/mm/fault.c
> > +++ b/arch/x86/mm/fault.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/mm_types.h>
> >  #include <linux/mm.h>                        /* find_and_lock_vma() */
> >  #include <linux/vmalloc.h>
> > +#include <linux/dept.h>
> >
> >  #include <asm/cpufeature.h>          /* boot_cpu_has, ...            */
> >  #include <asm/traps.h>                       /* dotraplinkage, ...           */
> > @@ -1219,6 +1220,12 @@ void do_user_addr_fault(struct pt_regs *regs,
> >       tsk = current;
> >       mm = tsk->mm;
> >
> > +     /*
> > +      * This fault comes from user mode.  Make dept work with a new
> > +      * kernel mode context.
> > +      */
> > +     dept_update_cxt();
> No, this fault does not come from user mode. That's why we call it "user
> addr" fault, not "user mode" fault. You end up here if, for instance,
> the kernel faults doing a copy_from_user().

My bad.  Thank you.  I will fix it.  Thank you very much.

	Byungchul