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Subject[PATCHv13 07/16] x86/mm: Reduce untagged_addr() overhead until the first LAM user
Date
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@linux.intel.com>
---
arch/x86/include/asm/uaccess.h | 9 +++++++--
arch/x86/kernel/process_64.c | 4 ++++
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index cbb463e9344f..1d931c7f6741 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 +33,11 @@ static inline bool pagefault_disabled(void);
*/
#define __untagged_addr(mm, addr) ({ \
u64 __addr = (__force u64)(addr); \
- s64 sign = (s64)__addr >> 63; \
- __addr &= READ_ONCE((mm)->context.untag_mask) | sign; \
+ if (static_branch_likely(&tagged_addr_key)) { \
+ s64 sign = (s64)__addr >> 63; \
+ u64 mask = READ_ONCE((mm)->context.untag_mask); \
+ __addr &= mask | sign; \
+ } \
(__force __typeof__(addr))__addr; \
})

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index fef127ed79b6..09e7f3d3fb5c 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);
+
#define LAM_U57_BITS 6

static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
@@ -773,6 +776,7 @@ static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)

mmap_write_unlock(mm);

+ static_branch_enable(&tagged_addr_key);
return 0;
}

--
2.38.2
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