From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
Borislav Petkov <bp@alien8.de>,
Linus Torvalds <torvalds@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>
Subject: Re: [RFC 1/2] x86/entry/64: Use the TSS sp2 slot for rsp_scratch
Date: Sun, 22 Jul 2018 22:12:11 +0200 [thread overview]
Message-ID: <20180722201211.GA30923@gmail.com> (raw)
In-Reply-To: <38b5a24f3c9f519dd7dc98171eb3a3c669fff48c.1532281180.git.luto@kernel.org>
* Andy Lutomirski <luto@kernel.org> wrote:
> In the non-trampoline SYSCALL64 path, we use a percpu variable to
> temporarily store the user RSP value. Instead of a separate
> variable, use the otherwise unused sp2 slot in the TSS. This will
> improve cache locality, as the sp1 slot is already used in the same
> code to find the kernel stack. It will also simplify a future
> change to make the non-trampoline path work in PTI mode.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/include/asm/processor.h | 5 +++++
> arch/x86/include/asm/thread_info.h | 1 +
> arch/x86/kernel/asm-offsets_64.c | 1 +
> arch/x86/kernel/process_64.c | 2 --
> 4 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index cfd29ee8c3da..2ef4c39ded45 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -308,7 +308,12 @@ struct x86_hw_tss {
> */
> u64 sp1;
>
> + /*
> + * sp2 is scratch space used by the SYSCALL64 handler. Linux does
> + * not use rung 2, so sp2 is not otherwise needed.
> + */
> u64 sp2;
s/rung/ring
Thanks,
Ingo
next prev parent reply other threads:[~2018-07-22 20:19 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-22 17:45 [RFC 0/2] Get rid of the entry trampoline Andy Lutomirski
2018-07-22 17:45 ` [RFC 1/2] x86/entry/64: Use the TSS sp2 slot for rsp_scratch Andy Lutomirski
2018-07-22 20:12 ` Ingo Molnar [this message]
2018-07-23 12:38 ` Dave Hansen
2018-07-24 2:36 ` Andy Lutomirski
2018-07-22 17:45 ` [RFC 2/2] x86/pti/64: Remove the SYSCALL64 entry trampoline Andy Lutomirski
2018-07-22 18:27 ` Linus Torvalds
2018-07-22 20:59 ` Andy Lutomirski
2018-07-23 12:59 ` Dave Hansen
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