From: Linus Torvalds <torvalds@linux-foundation.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: the arch/x86 maintainers <x86@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Kernel Hardening <kernel-hardening@lists.openwall.com>,
Borislav Petkov <bp@alien8.de>
Subject: [kernel-hardening] Re: [PATCH 2/3] x86/asm: Move 'status' from thread_struct to thread_info
Date: Sun, 28 Jan 2018 11:19:38 -0800 [thread overview]
Message-ID: <CA+55aFxhPk=9vk0_6XS82Kzxp8ncFzY3pvL8mh-zCYzsBJCFpA@mail.gmail.com> (raw)
In-Reply-To: <03148bcc1b217100e6e8ecf6a5468c45cf4304b6.1517164461.git.luto@kernel.org>
On Sun, Jan 28, 2018 at 10:38 AM, Andy Lutomirski <luto@kernel.org> wrote:
>
> 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.
Ack, that should be done separately from the movement anyway.
And yes, it's possible that once it's in the same cacheline with the
thread flags, you can't even see the issue anyway. Although I *think*
all those early fields are normally mostly read-only, so that "read
before clear" may end up being a good idea regardless.
Linus
next prev parent reply other threads:[~2018-01-28 19:19 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-28 18:38 [kernel-hardening] [PATCH 0/3] x86/pti-ish syscall cleanups Andy Lutomirski
2018-01-28 18:38 ` [kernel-hardening] [PATCH 1/3] x86/entry/64: Remove the SYSCALL64 fast path Andy Lutomirski
2018-01-28 19:00 ` [kernel-hardening] " Ingo Molnar
2018-01-28 18:38 ` [kernel-hardening] [PATCH 2/3] x86/asm: Move 'status' from thread_struct to thread_info Andy Lutomirski
2018-01-28 19:02 ` [kernel-hardening] " Ingo Molnar
2018-01-28 19:19 ` Linus Torvalds [this message]
2018-01-28 18:38 ` [kernel-hardening] [PATCH 3/3] syscalls: Add a bit of documentation to __SYSCALL_DEFINE Andy Lutomirski
2018-01-28 19:15 ` [kernel-hardening] " Linus Torvalds
2018-01-28 20:21 ` Al Viro
2018-01-28 20:42 ` Linus Torvalds
2018-01-28 22:50 ` Al Viro
2018-01-29 6:22 ` Al Viro
2018-01-28 19:21 ` Ingo Molnar
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