From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> mainline inclusion from mainline-v5.2-rc1 commit 577ff465f5a6a5a0866d75a033844810baca20a0 category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I4MKP4 CVE: NA -------------------------------- 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 Signed-off-by: Jackie Liu <liuyun01@kylinos.cn> #openEuler_contributor Signed-off-by: Laibin Qiu <qiulaibin@huawei.com> Reviewed-by: Wei Li <liwei391@huawei.com> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- arch/x86/include/asm/special_insns.h | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h index cddf923d405ce..b684dfdaaec1c 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); } -- 2.25.1