From: Andy Lutomirski <luto@kernel.org>
To: Fenghua Yu <fenghua.yu@intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Dave Hansen <dave.hansen@intel.com>,
H Peter Anvin <hpa@zytor.com>,
Jean-Philippe Brucker <jean-philippe@linaro.org>,
Dave Jiang <dave.jiang@intel.com>,
Ashok Raj <ashok.raj@intel.com>, x86 <x86@kernel.org>,
amd-gfx <amd-gfx@lists.freedesktop.org>,
Christoph Hellwig <hch@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
Borislav Petkov <bp@alien8.de>,
Thomas Gleixner <tglx@linutronix.de>,
Tony Luck <tony.luck@intel.com>,
Felix Kuehling <Felix.Kuehling@amd.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
iommu <iommu@lists.linux-foundation.org>,
Jacob Jun Pan <jacob.jun.pan@intel.com>,
David Woodhouse <dwmw2@infradead.org>
Subject: Re: [PATCH v6 09/12] x86/process: Clear PASID state for a newly forked/cloned thread
Date: Fri, 31 Jul 2020 18:44:55 -0700 [thread overview]
Message-ID: <CALCETrVZiCG4rcdMrs2F437oyBooQ2xt+feZLeK7qPk90gmOSw@mail.gmail.com> (raw)
In-Reply-To: <1594684087-61184-10-git-send-email-fenghua.yu@intel.com>
On Mon, Jul 13, 2020 at 4:48 PM Fenghua Yu <fenghua.yu@intel.com> wrote:
>
> The PASID state has to be cleared on forks, since the child has a
> different address space. The PASID is also cleared for thread clone. While
> it would be correct to inherit the PASID in this case, it is unknown
> whether the new task will use ENQCMD. Giving it the PASID "just in case"
> would have the downside of increased context switch overhead to setting
> the PASID MSR.
>
> Since #GP faults have to be handled on any threads that were created before
> the PASID was assigned to the mm of the process, newly created threads
> might as well be treated in a consistent way.
Just how much context switch overhead are we talking about here?
Unless the CPU works differently than I expect, I would guess you are
saving exactly zero cycles. What am I missing?
--Andy
>
> Suggested-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> ---
> v2:
> - Modify init_task_pasid().
>
> arch/x86/kernel/process.c | 18 ++++++++++++++++++
> 1 file changed, 18 insertions(+)
>
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index f362ce0d5ac0..1b1492e337a6 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -121,6 +121,21 @@ static int set_new_tls(struct task_struct *p, unsigned long tls)
> return do_set_thread_area_64(p, ARCH_SET_FS, tls);
> }
>
> +/* Initialize the PASID state for the forked/cloned thread. */
> +static void init_task_pasid(struct task_struct *task)
> +{
> + struct ia32_pasid_state *ppasid;
> +
> + /*
> + * Initialize the PASID state so that the PASID MSR will be
> + * initialized to its initial state (0) by XRSTORS when the task is
> + * scheduled for the first time.
> + */
> + ppasid = get_xsave_addr(&task->thread.fpu.state.xsave, XFEATURE_PASID);
> + if (ppasid)
> + ppasid->pasid = INIT_PASID;
> +}
> +
> int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
> unsigned long arg, struct task_struct *p, unsigned long tls)
> {
> @@ -174,6 +189,9 @@ int copy_thread_tls(unsigned long clone_flags, unsigned long sp,
> task_user_gs(p) = get_user_gs(current_pt_regs());
> #endif
>
> + if (static_cpu_has(X86_FEATURE_ENQCMD))
> + init_task_pasid(p);
> +
> /* Set a new TLS for the child thread? */
> if (clone_flags & CLONE_SETTLS)
> ret = set_new_tls(p, tls);
> --
> 2.19.1
>
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next prev parent reply other threads:[~2020-08-01 1:45 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-13 23:47 [PATCH v6 00/12] x86: tag application address space for devices Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 01/12] iommu: Change type of pasid to u32 Fenghua Yu
2020-07-14 2:45 ` Liu, Yi L
2020-07-14 13:54 ` Fenghua Yu
2020-07-14 13:56 ` Liu, Yi L
2020-07-22 14:03 ` Joerg Roedel
2020-07-22 17:21 ` Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 02/12] iommu/vt-d: Change flags type to unsigned int in binding mm Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 03/12] docs: x86: Add documentation for SVA (Shared Virtual Addressing) Fenghua Yu
2020-07-14 3:25 ` Liu, Yi L
2020-07-15 23:32 ` Fenghua Yu
2020-07-13 23:47 ` [PATCH v6 04/12] x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 05/12] x86/fpu/xstate: Add supervisor PASID state for ENQCMD feature Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 06/12] x86/msr-index: Define IA32_PASID MSR Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 07/12] mm: Define pasid in mm Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 08/12] fork: Clear PASID for new mm Fenghua Yu
2021-02-24 10:19 ` Jean-Philippe Brucker
2021-02-25 22:17 ` Fenghua Yu
2021-03-01 23:00 ` Jacob Pan
2021-03-02 10:43 ` Jean-Philippe Brucker
2020-07-13 23:48 ` [PATCH v6 09/12] x86/process: Clear PASID state for a newly forked/cloned thread Fenghua Yu
2020-08-01 1:44 ` Andy Lutomirski [this message]
2020-07-13 23:48 ` [PATCH v6 10/12] x86/mmu: Allocate/free PASID Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 11/12] sched: Define and initialize a flag to identify valid PASID in the task Fenghua Yu
2020-07-13 23:48 ` [PATCH v6 12/12] x86/traps: Fix up invalid PASID Fenghua Yu
2020-07-31 23:34 ` Andy Lutomirski
2020-08-01 0:42 ` Fenghua Yu
2020-08-03 15:03 ` Dave Hansen
2020-08-03 15:12 ` Andy Lutomirski
2020-08-03 15:19 ` Raj, Ashok
2020-08-03 16:36 ` Dave Hansen
2020-08-03 17:16 ` Andy Lutomirski
2020-08-03 17:34 ` Dave Hansen
2020-08-03 19:24 ` Andy Lutomirski
2020-08-01 1:28 ` Andy Lutomirski
2020-08-03 17:19 ` Fenghua Yu
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