mirror of
https://github.com/AuxXxilium/linux_dsm_epyc7002.git
synced 2024-12-15 20:56:44 +07:00
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
This commit is contained in:
parent
c806e88734
commit
577ff465f5
@ -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);
|
||||
}
|
||||
|
||||
|
Loading…
Reference in New Issue
Block a user