[PATCH 14/27] x86/pkeys: Don't check if PKRU is zero before writting it

Sebastian Andrzej Siewior
2019-04-03T16:43:32Z

write_pkru() checks if the current value is the same as the expected
value. So instead just checking if the current and new value is zero
(and skip the write in such a case) we can benefit from that.

Remove the zero check of PKRU, write_pkru() provides a similar check.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
arch/x86/mm/pkeys.c | 7 -------
1 file changed, 7 deletions(-)

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index 05bb9a44eb1c3..50f65fc1b9a3f 100644
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -142,13 +142,6 @@ u32 init_pkru_value = PKRU_AD_KEY( 1) | PKRU_AD_KEY( 2) | PKRU_AD_KEY( 3) |
void copy_init_pkru_to_fpregs(void)
{
u32 init_pkru_value_snapshot = READ_ONCE(init_pkru_value);
- /*
- * Any write to PKRU takes it out of the XSAVE 'init
- * state' which increases context switch cost. Avoid
- * writing 0 when PKRU was already 0.
- */
- if (!init_pkru_value_snapshot && !read_pkru())
- return;
/*
* Override the PKRU state that came from 'init_fpstate'
* with the baseline from the process.
--
2.20.1