Use static key to reduce untagged_addr() overhead.
The key only gets enabled when the first process enables LAM.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
---
arch/x86/include/asm/uaccess.h | 8 ++++++--
arch/x86/kernel/process_64.c | 4 ++++
2 files changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 0db6f5451854..1d2c79246681 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -23,6 +23,8 @@ static inline bool pagefault_disabled(void);
#endif
#ifdef CONFIG_X86_64
+DECLARE_STATIC_KEY_FALSE(tagged_addr_key);
+
/*
* Mask out tag bits from the address.
*
@@ -31,8 +33,10 @@ static inline bool pagefault_disabled(void);
*/
#define untagged_addr(mm, addr) ({ \
u64 __addr = (__force u64)(addr); \
- s64 sign = (s64)__addr >> 63; \
- __addr &= (mm)->context.untag_mask | sign; \
+ if (static_branch_likely(&tagged_addr_key)) { \
+ s64 sign = (s64)__addr >> 63; \
+ __addr &= (mm)->context.untag_mask | sign; \
+ } \
(__force __typeof__(addr))__addr; \
})
diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index b8f2558a3aeb..457f79be8bc7 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -743,6 +743,9 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
}
#endif
+DEFINE_STATIC_KEY_FALSE(tagged_addr_key);
+EXPORT_SYMBOL_GPL(tagged_addr_key);
+
static void enable_lam_func(void *mm)
{
struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
@@ -798,6 +801,7 @@ static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
}
on_each_cpu_mask(mm_cpumask(mm), enable_lam_func, mm, true);
+ static_branch_enable(&tagged_addr_key);
out:
mmap_write_unlock(mm);
return ret;
--
2.38.0
