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Subject[PATCH 1/2] x86: mmu.h: move mm_context_t::lock member inside CONFIG_MODIFY_LDT_SYSCALL
Date
The placement of the lock member in mm_context_t suggests that it is
used to protect the vdso* members, but AFAICT, it is only ever used
under #ifdef CONFIG_MODIFY_LDT_SYSCALL. So guarding the member by the
same config option is a cheap way to reduce sizeof(mm_struct) by 32
bytes (only for !CONFIG_MODIFY_LDT_SYSCALL kernels, of course).

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
---
arch/x86/include/asm/mmu.h | 11 ++++++++---
arch/x86/include/asm/mmu_context.h | 3 +--
2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/mmu.h b/arch/x86/include/asm/mmu.h
index e78c7db87801..b1bb47a3577b 100644
--- a/arch/x86/include/asm/mmu.h
+++ b/arch/x86/include/asm/mmu.h
@@ -30,14 +30,13 @@ typedef struct {
#ifdef CONFIG_MODIFY_LDT_SYSCALL
struct rw_semaphore ldt_usr_sem;
struct ldt_struct *ldt;
+ struct mutex lock;
#endif
-
#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 __user *vdso; /* vdso base address */
const struct vdso_image *vdso_image; /* vdso image in use */

@@ -56,10 +55,16 @@ typedef struct {
#endif
} mm_context_t;

+#ifdef CONFIG_MODIFY_LDT_SYSCALL
+#define INIT_MM_CONTEXT_LOCK(mm) .lock = __MUTEX_INITIALIZER(mm.context.lock),
+#else
+#define INIT_MM_CONTEXT_LOCK(mm)
+#endif
+
#define INIT_MM_CONTEXT(mm) \
.context = { \
.ctx_id = 1, \
- .lock = __MUTEX_INITIALIZER(mm.context.lock), \
+ INIT_MM_CONTEXT_LOCK(mm) \
}

void leave_mm(int cpu);
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index 9024236693d2..ac8e3ef8a774 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -82,6 +82,7 @@ static inline void init_new_context_ldt(struct mm_struct *mm)
{
mm->context.ldt = NULL;
init_rwsem(&mm->context.ldt_usr_sem);
+ mutex_init(&mm->context.lock);
}
int ldt_dup_context(struct mm_struct *oldmm, struct mm_struct *mm);
void destroy_context_ldt(struct mm_struct *mm);
@@ -186,8 +187,6 @@ void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk);
static inline int init_new_context(struct task_struct *tsk,
struct mm_struct *mm)
{
- mutex_init(&mm->context.lock);
-
mm->context.ctx_id = atomic64_inc_return(&last_mm_ctx_id);
atomic64_set(&mm->context.tlb_gen, 0);

--
2.20.1
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