From: Thomas Gleixner <tglx@linutronix.de>
To: "Chang S. Bae" <chang.seok.bae@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>, Ingo Molnar <mingo@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Andi Kleen <ak@linux.intel.com>,
Ravi Shankar <ravi.v.shankar@intel.com>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v7 07/18] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on
Date: Fri, 21 Jun 2019 17:22:09 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.21.1906211717500.5503@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1557309753-24073-8-git-send-email-chang.seok.bae@intel.com>
On Wed, 8 May 2019, Chang S. Bae wrote:
> From: Andy Lutomirski <luto@kernel.org>
>
> With the new FSGSBASE instructions, we can efficiently read and write
> the FSBASE and GSBASE in __switch_to(). Use that capability to preserve
> the full state.
>
> This will enable user code to do whatever it wants with the new
> instructions without any kernel-induced gotchas. (There can still be
> architectural gotchas: movl %gs,%eax; movl %eax,%gs may change GSBASE
> if WRGSBASE was used, but users are expected to read the CPU manual
> before doing things like that.)
>
> This is a considerable speedup. It seems to save about 100 cycles
> per context switch compared to the baseline 4.6-rc1 behavior on my
> Skylake laptop.
>
> [ chang: 5~10% performance improvements were seen by a context switch
> benchmark that ran threads with different FS/GSBASE values (to the
> baseline 4.16). Minor edit on the changelog. ]
>
> Signed-off-by: Andy Lutomirski <luto@kernel.org>
> Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Cc: H. Peter Anvin <hpa@zytor.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@kernel.org>
> ---
> arch/x86/kernel/process_64.c | 34 ++++++++++++++++++++++++++++------
> 1 file changed, 28 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
> index 17421c3..e2089c9 100644
> --- a/arch/x86/kernel/process_64.c
> +++ b/arch/x86/kernel/process_64.c
> @@ -239,8 +239,18 @@ static __always_inline void save_fsgs(struct task_struct *task)
> {
> savesegment(fs, task->thread.fsindex);
> savesegment(gs, task->thread.gsindex);
> - save_base_legacy(task, task->thread.fsindex, FS);
> - save_base_legacy(task, task->thread.gsindex, GS);
> + if (static_cpu_has(X86_FEATURE_FSGSBASE)) {
> + /*
> + * If FSGSBASE is enabled, we can't make any useful guesses
> + * about the base, and user code expects us to save the current
> + * value. Fortunately, reading the base directly is efficient.
> + */
> + task->thread.fsbase = rdfsbase();
> + task->thread.gsbase = __rdgsbase_inactive();
This explodes when called from copy_thread_tls() when an interrupt hits
after switching GS in __rdgsbase_inactive(). Wrapped it with
local_irq_save/restore().
Oh well.
Thanks,
tglx
next prev parent reply other threads:[~2019-06-21 15:22 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-08 10:02 [PATCH v7 00/18] x86: Enable FSGSBASE instructions Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 01/18] x86/fsgsbase/64: Fix ARCH_SET_FS/GS behaviors for a remote task Chang S. Bae
[not found] ` <74F4F506-2913-4013-9D81-A0C69FA8CDF1@intel.com>
[not found] ` <6420E1A5-B5AD-4028-AA91-AA4D5445AC83@intel.com>
2019-06-16 15:44 ` Bae, Chang Seok
2019-06-16 16:32 ` Thomas Gleixner
2019-06-22 10:04 ` [tip:x86/cpu] x86/ptrace: Prevent ptrace from clearing the FS/GS selector tip-bot for Chang S. Bae
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 02/18] selftests/x86/fsgsbase: Test ptracer-induced GSBASE write Chang S. Bae
2019-06-22 10:04 ` [tip:x86/cpu] " tip-bot for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 03/18] x86/fsgsbase/64: Add 'unsafe_fsgsbase' to enable CR4.FSGSBASE Chang S. Bae
2019-06-22 10:05 ` [tip:x86/cpu] x86/cpu: " tip-bot for Andy Lutomirski
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Andy Lutomirski
2019-05-08 10:02 ` [PATCH v7 04/18] kbuild: Raise the minimum required binutils version to 2.21 Chang S. Bae
2019-06-22 10:06 ` [tip:x86/cpu] " tip-bot for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 05/18] x86/fsgsbase/64: Add intrinsics for FSGSBASE instructions Chang S. Bae
2019-06-22 10:06 ` [tip:x86/cpu] " tip-bot for Andi Kleen
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Andi Kleen
2019-05-08 10:02 ` [PATCH v7 06/18] x86/fsgsbase/64: Enable FSGSBASE instructions in the helper functions Chang S. Bae
2019-06-22 10:07 ` [tip:x86/cpu] x86/fsgsbase/64: Enable FSGSBASE instructions in " tip-bot for Chang S. Bae
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 07/18] x86/fsgsbase/64: Preserve FS/GS state in __switch_to() if FSGSBASE is on Chang S. Bae
2019-06-21 15:22 ` Thomas Gleixner [this message]
2019-06-22 10:08 ` [tip:x86/cpu] x86/process/64: Use FSBSBASE in switch_to() if available tip-bot for Andy Lutomirski
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Andy Lutomirski
2019-05-08 10:02 ` [PATCH v7 08/18] x86/fsgsbase/64: When copying a thread, use the FSGSBASE instructions Chang S. Bae
2019-06-22 10:09 ` [tip:x86/cpu] x86/process/64: Use FSGSBASE instructions on thread copy and ptrace tip-bot for Chang S. Bae
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 09/18] x86/entry/64: Add the READ_MSR_GSBASE macro Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 10/18] x86/entry/64: Switch CR3 before SWAPGS on the paranoid entry Chang S. Bae
2019-06-22 10:09 ` [tip:x86/cpu] x86/entry/64: Switch CR3 before SWAPGS in " tip-bot for Chang S. Bae
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 11/18] x86/fsgsbase/64: Introduce the FIND_PERCPU_BASE macro Chang S. Bae
2019-06-22 10:10 ` [tip:x86/cpu] x86/entry/64: " tip-bot for Chang S. Bae
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 12/18] x86/fsgsbase/64: GSBASE handling with FSGSBASE in the paranoid path Chang S. Bae
2019-06-22 10:11 ` [tip:x86/cpu] x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit tip-bot for Chang S. Bae
2019-06-29 7:21 ` [PATCH v7 12/18] x86/fsgsbase/64: GSBASE handling with FSGSBASE in the paranoid path Bae, Chang Seok
2019-06-29 7:37 ` Thomas Gleixner
2020-06-18 13:50 ` [tip: x86/fsgsbase] x86/entry/64: Handle FSGSBASE enabled paranoid entry/exit tip-bot2 for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 13/18] x86/fsgsbase/64: Document GSBASE handling in the paranoid path Chang S. Bae
2019-06-22 10:11 ` [tip:x86/cpu] x86/entry/64: " tip-bot for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 14/18] selftests/x86/fsgsbase: Test WRGSBASE Chang S. Bae
2019-06-22 10:12 ` [tip:x86/cpu] selftests/x86/fsgsbase: Test RD/WRGSBASE tip-bot for Andy Lutomirski
2019-05-08 10:02 ` [PATCH v7 15/18] selftests/x86/fsgsbase: Test ptracer-induced GSBASE write with FSGSBASE Chang S. Bae
2019-06-22 10:13 ` [tip:x86/cpu] " tip-bot for Chang S. Bae
2019-05-08 10:02 ` [PATCH v7 16/18] x86/fsgsbase/64: Enable FSGSBASE by default and add a chicken bit Chang S. Bae
2019-06-22 10:14 ` [tip:x86/cpu] x86/cpu: Enable FSGSBASE on 64bit " tip-bot for Andy Lutomirski
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Andy Lutomirski
2019-05-08 10:02 ` [PATCH v7 17/18] x86/elf: Enumerate kernel FSGSBASE capability in AT_HWCAP2 Chang S. Bae
2019-06-22 10:14 ` [tip:x86/cpu] " tip-bot for Andi Kleen
2020-06-18 13:50 ` [tip: x86/fsgsbase] " tip-bot2 for Andi Kleen
2019-05-08 10:02 ` [PATCH v7 18/18] x86/fsgsbase/64: Add documentation for FSGSBASE Chang S. Bae
2019-06-14 6:54 ` Thomas Gleixner
2019-06-14 20:07 ` Bae, Chang Seok
[not found] ` <89BE934A-A392-4CED-83E5-CA4FADDAE6DF@intel.com>
2019-06-16 8:39 ` Thomas Gleixner
2019-06-16 12:34 ` Thomas Gleixner
2019-06-16 15:34 ` Bae, Chang Seok
2019-06-16 16:05 ` Thomas Gleixner
2019-06-16 20:48 ` Bae, Chang Seok
2019-06-16 22:00 ` Thomas Gleixner
[not found] ` <8E2E84B6-BCCC-424D-A1A7-604828B389FB@intel.com>
2019-06-17 5:18 ` Thomas Gleixner
2019-06-16 15:54 ` Randy Dunlap
2019-06-16 16:07 ` Thomas Gleixner
2019-06-22 10:15 ` [tip:x86/cpu] Documentation/x86/64: Add documentation for GS/FS addressing mode tip-bot for Thomas Gleixner
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