x86/pkeys: Don't check if PKRU is zero before writing it

write_pkru() checks if the current value is the same as the expected
value. So instead of 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 such a check now.

Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Signed-off-by: Borislav Petkov <[email protected]>
Reviewed-by: Dave Hansen <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "Jason A. Donenfeld" <[email protected]>
Cc: kvm ML <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: x86-ml <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]

1 files changed, 0 insertions, 7 deletions

diff --git a/arch/x86/mm/pkeys.c b/arch/x86/mm/pkeys.c
index 05bb9a44eb1c..50f65fc1b9a3 100644
--- 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.
 	 */