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
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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 --- 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 cddf923d405c..b684dfdaaec1 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); }