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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 19 Oct 2018 13:59:26 +0200
Subject: [PATCH 14/27] x86/pkeys: Don't check if PKRU is zero before writting
it
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/5.0/older/patches-5.0.7-rt5.tar.xz
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(-)
--- a/arch/x86/mm/pkeys.c
+++ b/arch/x86/mm/pkeys.c
@@ -143,13 +143,6 @@ 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.
*/
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