From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Rik van Riel" <riel@redhat.com>,
"Oleg Nesterov" <oleg@redhat.com>,
"Denys Vlasenko" <vda.linux@googlemail.com>,
"Borislav Petkov" <bp@alien8.de>,
"Kees Cook" <keescook@chromium.org>,
"Brian Gerst" <brgerst@gmail.com>,
"Linus Torvalds" <torvalds@linux-foundation.org>
Subject: Re: [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks
Date: Wed, 17 Jun 2015 12:00:09 +0200 [thread overview]
Message-ID: <20150617100009.GA5673@gmail.com> (raw)
In-Reply-To: <0ee44a97cf6ffd9a948425b27fa8d48fa271c440.1434485184.git.luto@kernel.org>
* Andy Lutomirski <luto@kernel.org> wrote:
> This is separate for ease of bisection.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/entry/entry_64.S | 68 +++++------------------------------------------
> 1 file changed, 7 insertions(+), 61 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 33acc3dcc281..a5044d7a9d43 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -229,6 +229,11 @@ entry_SYSCALL_64_fastpath:
> */
> USERGS_SYSRET64
>
> +GLOBAL(int_ret_from_sys_call_irqs_off)
> + TRACE_IRQS_ON
> + ENABLE_INTERRUPTS(CLBR_NONE)
> + jmp int_ret_from_sys_call
Any reason why irq state tracking cannot be done in C as well, like the rest of
the irq state tracking code?
(Btw., context tracking could in theory be merged with irq state tracking, they
have similar needs.)
One complication would be that we have not saved pt_regs yet:
> @@ -272,69 +277,10 @@ tracesys_phase2:
> * Has correct iret frame.
> */
> GLOBAL(int_ret_from_sys_call)
> SAVE_EXTRA_REGS
> + movq %rsp, %rdi
> + call syscall_return_slowpath /* returns with IRQs disabled */
> RESTORE_EXTRA_REGS
... but we can stipulate that IRQs can be enabled after we've constructed pt_regs.
The few cycles constant added latency there isn't an issue - maintainability of
the code is.
... this would also allow us to get rid of paravirt interface uglies like
'CLBR_NONE' which has no place in generic entry code.
With such a conversion very little 'high level, complex logic' should be left in
assembly and as much as possible should be moved to C: that way we can integrate
it all on the C level and achieve similar speedups as with assembly. Half-done
will reduce that potential of speedups through integration.
A bit like how we have done it with do_page_fault(): there's very little left at
the assembly level, still it has not kept people from micro-optimizing the heck
out of the low level page fault code.
Thanks,
Ingo
next prev parent reply other threads:[~2015-06-17 10:00 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-16 20:16 [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 01/13] context_tracking: Add context_tracking_assert_state Andy Lutomirski
2015-06-17 9:41 ` Ingo Molnar
2015-06-17 14:15 ` Andy Lutomirski
2015-06-18 9:57 ` Ingo Molnar
2015-06-18 11:07 ` Andy Lutomirski
2015-06-18 15:52 ` Andy Lutomirski
2015-06-18 16:17 ` Ingo Molnar
2015-06-18 16:26 ` Frederic Weisbecker
2015-06-18 19:26 ` Andy Lutomirski
2015-06-17 15:27 ` Paul E. McKenney
2015-06-18 9:59 ` Ingo Molnar
2015-06-18 22:54 ` Paul E. McKenney
2015-06-19 2:19 ` Paul E. McKenney
2015-06-30 11:04 ` Ingo Molnar
2015-06-30 16:16 ` Paul E. McKenney
2015-06-16 20:16 ` [RFC/INCOMPLETE 02/13] notifiers: Assert that RCU is watching in notify_die Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 03/13] x86: Move C entry and exit code to arch/x86/entry/common.c Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 04/13] x86/traps: Assert that we're in CONTEXT_KERNEL in exception entries Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 05/13] x86/entry: Add enter_from_user_mode and use it in syscalls Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 06/13] x86/entry: Add new, comprehensible entry and exit hooks Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 07/13] x86/entry/64: Really create an error-entry-from-usermode code path Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 08/13] x86/entry/64: Migrate 64-bit syscalls to new exit hooks Andy Lutomirski
2015-06-17 10:00 ` Ingo Molnar [this message]
2015-06-17 10:02 ` Ingo Molnar
2015-06-17 14:12 ` Andy Lutomirski
2015-06-18 10:17 ` Ingo Molnar
2015-06-18 10:19 ` Ingo Molnar
2015-06-16 20:16 ` [RFC/INCOMPLETE 09/13] x86/entry/compat: Migrate compat " Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 10/13] x86/asm/entry/64: Save all regs on interrupt entry Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 11/13] x86/asm/entry/64: Simplify irq stack pt_regs handling Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 12/13] x86/asm/entry/64: Migrate error and interrupt exit work to C Andy Lutomirski
2015-06-16 20:16 ` [RFC/INCOMPLETE 13/13] x86/entry: Remove SCHEDULE_USER and asm/context-tracking.h Andy Lutomirski
2015-06-17 9:48 ` [RFC/INCOMPLETE 00/13] x86: Rewrite exit-to-userspace code Ingo Molnar
2015-06-17 10:13 ` Richard Weinberger
2015-06-17 11:04 ` Ingo Molnar
2015-06-17 14:19 ` Andy Lutomirski
2015-06-17 15:16 ` Andy Lutomirski
2015-06-18 10:14 ` Ingo Molnar
2015-06-17 10:32 ` Ingo Molnar
2015-06-17 11:14 ` Ingo Molnar
2015-06-17 14:23 ` Andy Lutomirski
2015-06-18 10:11 ` Ingo Molnar
2015-06-18 11:06 ` Andy Lutomirski
2015-06-18 16:24 ` Ingo Molnar
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