From: Brian Gerst <brgerst@gmail.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: X86 ML <x86@kernel.org>, Borislav Petkov <bpetkov@suse.de>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Dave Hansen <dave.hansen@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 07/18] x86/asm/64: Merge the fast and slow SYSRET paths
Date: Wed, 1 Nov 2017 13:25:22 -0400 [thread overview]
Message-ID: <CAMzpN2hw6q5G7A-2vb7mHqECf4-Vd8D7XEVGXg7U-Mi06qY_4w@mail.gmail.com> (raw)
In-Reply-To: <998a8c2c39546115f93e4c6e2ad7f918626f6145.1509006199.git.luto@kernel.org>
On Thu, Oct 26, 2017 at 4:26 AM, Andy Lutomirski <luto@kernel.org> wrote:
> They did almost the same thing. Remove a bunch of pointless
> instructions (mostly hidden in macros) and reduce cognitive load by
> merging them.
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> ---
> arch/x86/entry/entry_64.S | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 9dafafa3e0ec..c855ee91a3a5 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -220,10 +220,9 @@ entry_SYSCALL_64_fastpath:
> TRACE_IRQS_ON /* user mode is traced as IRQs on */
> movq RIP(%rsp), %rcx
> movq EFLAGS(%rsp), %r11
> - RESTORE_C_REGS_EXCEPT_RCX_R11
> - movq RSP(%rsp), %rsp
> + addq $6*8, %rsp /* skip extra regs -- they were preserved */
> UNWIND_HINT_EMPTY
> - USERGS_SYSRET64
> + jmp .Lpop_c_regs_except_rcx_r11_and_sysret
>
> 1:
> /*
> @@ -315,6 +314,7 @@ syscall_return_via_sysret:
> /* rcx and r11 are already restored (see code above) */
> UNWIND_HINT_EMPTY
> POP_EXTRA_REGS
> +.Lpop_c_regs_except_rcx_r11_and_sysret:
> popq %rsi /* skip r11 */
> popq %r10
> popq %r9
Wouldn't it be more logical to keep the SYSRET path at the end of the
fast path (reverse of what you are doing here)? That way the fast
path falls through without jumping.
--
Brian Gerst
next prev parent reply other threads:[~2017-11-01 17:25 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 8:26 [PATCH 00/18] Pile o' entry/exit/sp0 changes Andy Lutomirski
2017-10-26 8:26 ` [PATCH 01/18] x86/asm/64: Remove the restore_c_regs_and_iret label Andy Lutomirski
2017-10-26 15:07 ` Borislav Petkov
2017-11-10 6:08 ` [01/18] " kemi
2017-10-26 8:26 ` [PATCH 02/18] x86/asm/64: Split the iret-to-user and iret-to-kernel paths Andy Lutomirski
2017-10-27 18:05 ` Dave Hansen
2017-11-01 11:34 ` Andy Lutomirski
2017-10-27 20:04 ` Borislav Petkov
2017-11-01 11:32 ` Andy Lutomirski
2017-10-26 8:26 ` [PATCH 03/18] x86/asm/64: Move SWAPGS into the common iret-to-usermode path Andy Lutomirski
2017-10-26 13:52 ` Brian Gerst
2017-10-26 14:13 ` Dave Hansen
2017-10-26 14:28 ` Borislav Petkov
2017-10-27 15:44 ` Andy Lutomirski
2017-10-27 18:08 ` Dave Hansen
2017-10-26 8:26 ` [PATCH 04/18] x86/asm/64: Simplify reg restore code in the standard IRET paths Andy Lutomirski
2017-10-26 8:26 ` [PATCH 05/18] x86/asm/64: Shrink paranoid_exit_restore and make labels local Andy Lutomirski
2017-10-27 20:07 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 06/18] x86/asm/64: Use pop instead of movq in syscall_return_via_sysret Andy Lutomirski
2017-10-27 20:11 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 07/18] x86/asm/64: Merge the fast and slow SYSRET paths Andy Lutomirski
2017-10-27 20:11 ` Borislav Petkov
2017-11-01 11:29 ` Andy Lutomirski
2017-11-01 12:35 ` Borislav Petkov
2017-11-01 17:26 ` Thomas Gleixner
2017-11-01 17:25 ` Brian Gerst [this message]
2017-11-01 20:35 ` Andy Lutomirski
2017-10-26 8:26 ` [PATCH 08/18] xen: add xen nmi trap entry Andy Lutomirski
2017-10-26 8:26 ` [PATCH 09/18] x86/asm/64: De-Xen-ify our NMI code Andy Lutomirski
2017-10-26 8:41 ` Juergen Gross
2017-10-27 20:11 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 10/18] x86/asm/32: Pull MSR_IA32_SYSENTER_CS update code out of native_load_sp0() Andy Lutomirski
2017-10-26 18:00 ` Brian Gerst
2017-10-27 13:51 ` Thomas Gleixner
2017-10-27 15:50 ` Andy Lutomirski
2017-10-27 20:11 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 11/18] x86/asm/64: Pass sp0 directly to load_sp0() Andy Lutomirski
2017-10-27 20:12 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 12/18] x86/asm: Add task_top_of_stack() to find the top of a task's stack Andy Lutomirski
2017-10-26 8:26 ` [PATCH 13/18] x86/xen/64: Clean up SP code in cpu_initialize_context() Andy Lutomirski
2017-10-26 8:43 ` Juergen Gross
2017-10-26 8:26 ` [PATCH 14/18] x86/boot/64: Stop initializing TSS.sp0 at boot Andy Lutomirski
2017-10-27 18:21 ` Dave Hansen
2017-10-28 8:10 ` Andy Lutomirski
2017-10-26 8:26 ` [PATCH 15/18] x86/asm/64: Remove all remaining direct thread_struct::sp0 reads Andy Lutomirski
2017-11-01 10:08 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 16/18] x86/boot/32: Fix cpu_current_top_of_stack initialization at boot Andy Lutomirski
2017-11-01 10:18 ` Borislav Petkov
2017-10-26 8:26 ` [PATCH 17/18] x86/asm/64: Remove thread_struct::sp0 Andy Lutomirski
2017-10-28 0:52 ` Brian Gerst
2017-11-01 10:23 ` Borislav Petkov
2017-11-01 10:40 ` Andy Lutomirski
2017-10-26 8:26 ` [PATCH 18/18] x86/traps: Use a new on_thread_stack() helper to clean up an assertion Andy Lutomirski
2017-11-01 10:31 ` Borislav Petkov
2017-11-01 10:45 ` Andy Lutomirski
2017-10-26 15:55 ` [PATCH 00/18] Pile o' entry/exit/sp0 changes Linus Torvalds
2017-10-28 7:31 ` Andy Lutomirski
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