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SubjectQ: x86: add context tag to mark mm when running a task in 32-bit compatibility mode
commit c2ef45df3b98a027ec8f9081bd2a19dff520ef9d

This tag is intended to mirror the thread info TIF_IA32 flag.

OK, but

+#ifdef CONFIG_X86_64
+ /* True if mm supports a task running in 32 bit compatibility mode. */
+ unsigned short ia32_compat;
+#endif
Stupid question, why we can't add a simple arch-independent MMF_COMPAT
flag instead?

I am asking because we probably want to backport this change and this
ia32_compat looks a bit annoying, why should we waste a word?

Sure, this is very minor, but perhaps the trivial patch below makes
sense?

Oleg.


--- x/include/linux/sched.h
+++ x/include/linux/sched.h
@@ -436,6 +436,8 @@ extern int get_dumpable(struct mm_struct
#define MMF_VM_MERGEABLE 16 /* KSM may merge identical pages */
#define MMF_VM_HUGEPAGE 17 /* set when VM_HUGEPAGE is set on vma */

+#define MMF_COMPAT 18 /* this task runs in compat mode. */
+
#define MMF_INIT_MASK (MMF_DUMPABLE_MASK | MMF_DUMP_FILTER_MASK)

struct sighand_struct {
--- x/arch/x86/include/asm/mmu.h
+++ x/arch/x86/include/asm/mmu.h
@@ -12,11 +12,6 @@ typedef struct {
void *ldt;
int size;

-#ifdef CONFIG_X86_64
- /* True if mm supports a task running in 32 bit compatibility mode. */
- unsigned short ia32_compat;
-#endif
-
struct mutex lock;
void *vdso;
} mm_context_t;
--- x/arch/x86/kernel/process_64.c
+++ x/arch/x86/kernel/process_64.c
@@ -502,10 +502,6 @@ void set_personality_64bit(void)
/* Make sure to be in 64bit mode */
clear_thread_flag(TIF_IA32);

- /* Ensure the corresponding mm is not marked. */
- if (current->mm)
- current->mm->context.ia32_compat = 0;
-
/* TBD: overwrites user setup. Should have two bits.
But 64bit processes have always behaved this way,
so it's not too bad. The main problem is just that
@@ -522,8 +518,7 @@ void set_personality_ia32(void)
current->personality |= force_personality32;

/* Mark the associated mm as containing 32-bit tasks. */
- if (current->mm)
- current->mm->context.ia32_compat = 1;
+ set_bit(MMF_COMPAT, &current->mm->flags);

/* Prepare the first "return" to user space */
current_thread_info()->status |= TS_COMPAT;
--- x/arch/x86/mm/init_64.c
+++ x/arch/x86/mm/init_64.c
@@ -860,7 +860,7 @@ static struct vm_area_struct gate_vma =
struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
{
#ifdef CONFIG_IA32_EMULATION
- if (!mm || mm->context.ia32_compat)
+ if (!mm || test_bit(MMF_COMPAT, &mm->flags))
return NULL;
#endif
return &gate_vma;
--- x/arch/x86/ia32/ia32_aout.c
+++ x/arch/x86/ia32/ia32_aout.c
@@ -298,7 +298,7 @@ static int load_aout_binary(struct linux
/* OK, This is the point of no return */
set_personality(PER_LINUX);
set_thread_flag(TIF_IA32);
- current->mm->context.ia32_compat = 1;
+ set_bit(MMF_COMPAT, &current->mm->flags);

setup_new_exec(bprm);



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