From mboxrd@z Thu Jan 1 00:00:00 1970 Sender: Ingo Molnar Date: Sun, 28 Jan 2018 20:02:43 +0100 From: Ingo Molnar Message-ID: <20180128190243.gp3ner27uhsnnjpb@gmail.com> References: <03148bcc1b217100e6e8ecf6a5468c45cf4304b6.1517164461.git.luto@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <03148bcc1b217100e6e8ecf6a5468c45cf4304b6.1517164461.git.luto@kernel.org> Subject: [kernel-hardening] Re: [PATCH 2/3] x86/asm: Move 'status' from thread_struct to thread_info To: Andy Lutomirski Cc: x86@kernel.org, LKML , Linus Torvalds , Kernel Hardening , Borislav Petkov List-ID: * Andy Lutomirski wrote: > The TS_COMPAT bit is very hot and is accessed from code paths that > mostly also touch thread_info::flags. Move it into struct > thread_info to improve cache locality. > > The only reason it was in thread_struct is that there was a brief > period during which we didn't allow arch-specific fields in struct > thread_info. > > Linus suggested further changing: > > ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); > > to: > > if (unlikely(ti->status & (TS_COMPAT|TS_I386_REGS_POKED))) > ti->status &= ~(TS_COMPAT|TS_I386_REGS_POKED); > > on the theory that frequently dirtying the cacheline even in pure > 64-bit code that never needs to modify status hurts performance. > That could be a reasonable followup patch, but I suspect it matters > less on top of this patch. > > Suggested-by: Linus Torvalds > Signed-off-by: Andy Lutomirski > --- > arch/x86/entry/common.c | 4 ++-- > arch/x86/include/asm/processor.h | 2 -- > arch/x86/include/asm/syscall.h | 6 +++--- > arch/x86/include/asm/thread_info.h | 3 ++- > arch/x86/kernel/process_64.c | 4 ++-- > arch/x86/kernel/ptrace.c | 2 +- > arch/x86/kernel/signal.c | 2 +- > 7 files changed, 11 insertions(+), 12 deletions(-) Reviewed-by: Ingo Molnar Thanks, Ingo