From: Thomas Gleixner <tglx@linutronix.de>
To: Sohil Mehta <sohil.mehta@intel.com>, x86@kernel.org
Cc: Sohil Mehta <sohil.mehta@intel.com>,
Tony Luck <tony.luck@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
"H . Peter Anvin" <hpa@zytor.com>,
Andy Lutomirski <luto@kernel.org>, Jens Axboe <axboe@kernel.dk>,
Christian Brauner <christian@brauner.io>,
Peter Zijlstra <peterz@infradead.org>,
Shuah Khan <shuah@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Jonathan Corbet <corbet@lwn.net>, Ashok Raj <ashok.raj@intel.com>,
Jacob Pan <jacob.jun.pan@linux.intel.com>,
Gayatri Kammela <gayatri.kammela@intel.com>,
Zeng Guang <guang.zeng@intel.com>,
Dan Williams <dan.j.williams@intel.com>,
Randy E Witt <randy.e.witt@intel.com>,
Ravi V Shankar <ravi.v.shankar@intel.com>,
Ramesh Thomas <ramesh.thomas@intel.com>,
linux-api@vger.kernel.org, linux-arch@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org
Subject: Re: [RFC PATCH 05/13] x86/irq: Reserve a user IPI notification vector
Date: Fri, 24 Sep 2021 01:07:47 +0200 [thread overview]
Message-ID: <87fstugabg.ffs@tglx> (raw)
In-Reply-To: <20210913200132.3396598-6-sohil.mehta@intel.com>
On Mon, Sep 13 2021 at 13:01, Sohil Mehta wrote:
> A user interrupt notification vector is used on the receiver's cpu to
> identify an interrupt as a user interrupt (and not a kernel interrupt).
> Hardware uses the same notification vector to generate an IPI from a
> sender's cpu core when the SENDUIPI instruction is executed.
>
> Typically, the kernel shouldn't receive an interrupt with this vector.
> However, it is possible that the kernel might receive this vector.
>
> Scenario that can cause the spurious interrupt:
>
> Step cpu 0 (receiver task) cpu 1 (sender task)
> ---- --------------------- -------------------
> 1 task is running
> 2 executes SENDUIPI
> 3 IPI sent
> 4 context switched out
> 5 IPI delivered
> (kernel interrupt detected)
>
> A kernel interrupt can be detected, if a receiver task gets scheduled
> out after the SENDUIPI-based IPI was sent but before the IPI was
> delivered.
What happens if the SENDUIPI is issued when the target task is not on
the CPU? How is that any different from the above?
> The kernel doesn't need to do anything in this case other than receiving
> the interrupt and clearing the local APIC. The user interrupt is always
> stored in the receiver's UPID before the IPI is generated. When the
> receiver gets scheduled back the interrupt would be delivered based on
> its UPID.
So why on earth is that vector reaching the CPU at all?
> +#ifdef CONFIG_X86_USER_INTERRUPTS
> + seq_printf(p, "%*s: ", prec, "UIS");
No point in printing that when user interrupts are not available/enabled
on the system.
> + for_each_online_cpu(j)
> + seq_printf(p, "%10u ", irq_stats(j)->uintr_spurious_count);
> + seq_puts(p, " User-interrupt spurious event\n");
> #endif
> return 0;
> }
> @@ -325,6 +331,33 @@ DEFINE_IDTENTRY_SYSVEC_SIMPLE(sysvec_kvm_posted_intr_nested_ipi)
> }
> #endif
>
> +#ifdef CONFIG_X86_USER_INTERRUPTS
> +/*
> + * Handler for UINTR_NOTIFICATION_VECTOR.
> + *
> + * The notification vector is used by the cpu to detect a User Interrupt. In
> + * the typical usage, the cpu would handle this interrupt and clear the local
> + * apic.
> + *
> + * However, it is possible that the kernel might receive this vector. This can
> + * happen if the receiver thread was running when the interrupt was sent but it
> + * got scheduled out before the interrupt was delivered. The kernel doesn't
> + * need to do anything other than clearing the local APIC. A pending user
> + * interrupt is always saved in the receiver's UPID which can be referenced
> + * when the receiver gets scheduled back.
> + *
> + * If the kernel receives a storm of these, it could mean an issue with the
> + * kernel's saving and restoring of the User Interrupt MSR state; Specifically,
> + * the notification vector bits in the IA32_UINTR_MISC_MSR.
Definitely well thought out hardware that.
Thanks,
tglx
next prev parent reply other threads:[~2021-09-23 23:07 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-13 20:01 [RFC PATCH 00/13] x86 User Interrupts support Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 01/13] x86/uintr/man-page: Include man pages draft for reference Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 02/13] Documentation/x86: Add documentation for User Interrupts Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 03/13] x86/cpu: Enumerate User Interrupts support Sohil Mehta
2021-09-23 22:24 ` Thomas Gleixner
2021-09-24 19:59 ` Sohil Mehta
2021-09-27 20:42 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 04/13] x86/fpu/xstate: Enumerate User Interrupts supervisor state Sohil Mehta
2021-09-23 22:34 ` Thomas Gleixner
2021-09-27 22:25 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 05/13] x86/irq: Reserve a user IPI notification vector Sohil Mehta
2021-09-23 23:07 ` Thomas Gleixner [this message]
2021-09-25 13:30 ` Thomas Gleixner
2021-09-26 12:39 ` Thomas Gleixner
2021-09-27 19:07 ` Sohil Mehta
2021-09-28 8:11 ` Thomas Gleixner
2021-09-27 19:26 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 06/13] x86/uintr: Introduce uintr receiver syscalls Sohil Mehta
2021-09-23 12:26 ` Greg KH
2021-09-24 0:05 ` Thomas Gleixner
2021-09-27 23:20 ` Sohil Mehta
2021-09-28 4:39 ` Greg KH
2021-09-28 16:47 ` Sohil Mehta
2021-09-23 23:52 ` Thomas Gleixner
2021-09-27 23:57 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 07/13] x86/process/64: Add uintr task context switch support Sohil Mehta
2021-09-24 0:41 ` Thomas Gleixner
2021-09-28 0:30 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 08/13] x86/process/64: Clean up uintr task fork and exit paths Sohil Mehta
2021-09-24 1:02 ` Thomas Gleixner
2021-09-28 1:23 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 09/13] x86/uintr: Introduce vector registration and uintr_fd syscall Sohil Mehta
2021-09-24 10:33 ` Thomas Gleixner
2021-09-28 20:40 ` Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 10/13] x86/uintr: Introduce user IPI sender syscalls Sohil Mehta
2021-09-23 12:28 ` Greg KH
2021-09-28 18:01 ` Sohil Mehta
2021-09-29 7:04 ` Greg KH
2021-09-29 14:27 ` Sohil Mehta
2021-09-24 10:54 ` Thomas Gleixner
2021-09-13 20:01 ` [RFC PATCH 11/13] x86/uintr: Introduce uintr_wait() syscall Sohil Mehta
2021-09-24 11:04 ` Thomas Gleixner
2021-09-25 12:08 ` Thomas Gleixner
2021-09-28 23:13 ` Sohil Mehta
2021-09-28 23:08 ` Sohil Mehta
2021-09-26 14:41 ` Thomas Gleixner
2021-09-29 1:09 ` Sohil Mehta
2021-09-29 3:30 ` Andy Lutomirski
2021-09-29 4:56 ` Sohil Mehta
2021-09-30 18:08 ` Andy Lutomirski
2021-09-30 19:29 ` Thomas Gleixner
2021-09-30 22:01 ` Andy Lutomirski
2021-10-01 0:01 ` Thomas Gleixner
2021-10-01 4:41 ` Andy Lutomirski
2021-10-01 9:56 ` Thomas Gleixner
2021-10-01 15:13 ` Andy Lutomirski
2021-10-01 18:04 ` Sohil Mehta
2021-10-01 21:29 ` Thomas Gleixner
2021-10-01 23:00 ` Sohil Mehta
2021-10-01 23:04 ` Andy Lutomirski
2021-09-13 20:01 ` [RFC PATCH 12/13] x86/uintr: Wire up the user interrupt syscalls Sohil Mehta
2021-09-13 20:01 ` [RFC PATCH 13/13] selftests/x86: Add basic tests for User IPI Sohil Mehta
2021-09-13 20:27 ` [RFC PATCH 00/13] x86 User Interrupts support Dave Hansen
2021-09-14 19:03 ` Mehta, Sohil
2021-09-23 12:19 ` Greg KH
2021-09-23 14:09 ` Greg KH
2021-09-23 14:46 ` Dave Hansen
2021-09-23 15:07 ` Greg KH
2021-09-23 23:24 ` Sohil Mehta
2021-09-23 23:09 ` Sohil Mehta
2021-09-24 0:17 ` Sohil Mehta
2021-09-23 14:39 ` Jens Axboe
2021-09-29 4:31 ` Andy Lutomirski
2021-09-30 16:30 ` Stefan Hajnoczi
2021-09-30 17:24 ` Sohil Mehta
2021-09-30 17:26 ` Andy Lutomirski
2021-10-01 16:35 ` Stefan Hajnoczi
2021-10-01 16:41 ` Richard Henderson
2021-09-30 16:26 ` Stefan Hajnoczi
2021-10-01 0:40 ` Sohil Mehta
2021-10-01 8:19 ` Pavel Machek
2021-11-18 22:19 ` Sohil Mehta
2021-11-16 3:49 ` Prakash Sangappa
2021-11-18 21:44 ` Sohil Mehta
2021-12-22 16:17 ` Chrisma Pakha
2022-01-07 2:08 ` Sohil Mehta
2022-01-17 1:14 ` Chrisma Pakha
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