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| author | Sebastian Andrzej Siewior <bigeasy@linutronix.de> | 2019-04-03 18:41:42 +0200 |
|---|---|---|
| committer | Borislav Petkov <bp@suse.de> | 2019-04-11 15:41:05 +0200 |
| commit | 577ff465f5a6a5a0866d75a033844810baca20a0 (patch) | |
| tree | 67cd0094d0e6fc68d212a9ed0737cb24354ef1bc /arch/x86/include | |
| parent | x86/pkeys: Provide *pkru() helpers (diff) | |
| download | linux-577ff465f5a6a5a0866d75a033844810baca20a0.tar.xz linux-577ff465f5a6a5a0866d75a033844810baca20a0.zip | |
x86/fpu: Only write PKRU if it is different from current
According to Dave Hansen, WRPKRU is more expensive than RDPKRU. It has
a higher cycle cost and it's also practically a (light) speculation
barrier.
As an optimisation read the current PKRU value and only write the new
one if it is different.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: kvm ML <kvm@vger.kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@surriel.com>
Cc: x86-ml <x86@kernel.org>
Link: https://lkml.kernel.org/r/20190403164156.19645-14-bigeasy@linutronix.de
Diffstat (limited to 'arch/x86/include')
| -rw-r--r-- | arch/x86/include/asm/special_insns.h | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index 34897e2b52c9..0a3c4cab39db 100644 --- a/arch/x86/include/asm/special_insns.h +++ b/arch/x86/include/asm/special_insns.h @@ -121,6 +121,13 @@ static inline void wrpkru(u32 pkru) static inline void __write_pkru(u32 pkru) { + /* + * WRPKRU is relatively expensive compared to RDPKRU. + * Avoid WRPKRU when it would not change the value. + */ + if (pkru == rdpkru()) + return; + wrpkru(pkru); } |