Re: NMI for ARC

On Thu, Sep 29, 2016 at 12:48:03PM -0700, Vineet Gupta wrote: > > [1] There's an exception on 64-bit AMD CPUs because AMD blew it. > > Also, x86 NMI return is itself severely overcomplicated because we don't > > have good control over NMI nesting. > > For ARC (HS38 cores)

Re: NMI for ARC

On Thu, Sep 29, 2016 at 12:48:03PM -0700, Vineet Gupta wrote: > > [1] There's an exception on 64-bit AMD CPUs because AMD blew it. > > Also, x86 NMI return is itself severely overcomplicated because we don't > > have good control over NMI nesting. > > For ARC (HS38 cores)

Re: NMI for ARC

eempt_count(NMI_OFFSET) in entry of nmi handler. > The perf NMI code won't schedule. In general, you just need to ensure > that is_nmi() is true. Any kernel code that touches normal locks, > schedules, gets page faults without extreme caution, etc. needs to be > aware that nmis are s

Re: NMI for ARC

eempt_count(NMI_OFFSET) in entry of nmi handler. > The perf NMI code won't schedule. In general, you just need to ensure > that is_nmi() is true. Any kernel code that touches normal locks, > schedules, gets page faults without extreme caution, etc. needs to be > aware that nmis are s

Re: NMI for ARC

On Thu, Sep 29, 2016 at 9:47 AM, Vineet Gupta wrote: > On 09/28/2016 11:43 PM, Peter Zijlstra wrote: >> On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: >>> On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> >> >> userirq nmi >> >> |

Re: NMI for ARC

On Thu, Sep 29, 2016 at 9:47 AM, Vineet Gupta wrote: > On 09/28/2016 11:43 PM, Peter Zijlstra wrote: >> On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: >>> On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> >> >> userirq nmi >> >> | >> | >> `-> .

Re: NMI for ARC

On Sep 28, 2016 6:20 PM, "Vineet Gupta" wrote: > > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> Right, so what I think Vineet is asking is if we need to disable NMIs as > >> > well, we cannot on x86 disable NMIs so no. > >> > > > The same argument works here, too: an

Re: NMI for ARC

On Sep 28, 2016 6:20 PM, "Vineet Gupta" wrote: > > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> Right, so what I think Vineet is asking is if we need to disable NMIs as > >> > well, we cannot on x86 disable NMIs so no. > >> > > > The same argument works here, too: an NMI won't set

Re: NMI for ARC

On 09/28/2016 11:43 PM, Peter Zijlstra wrote: > On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: >> On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > > > userirq nmi > > | > | > `-> . > | > | > | >

Re: NMI for ARC

On 09/28/2016 11:43 PM, Peter Zijlstra wrote: > On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: >> On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > > > userirq nmi > > | > | > `-> . > | > | > | >

Re: NMI for ARC

On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> Right, so what I think Vineet is asking is if we need to disable NMIs as > >> > well, we cannot on x86 disable NMIs so no. > >> > > > The same argument works here, too: an NMI won't

Re: NMI for ARC

On Wed, Sep 28, 2016 at 06:20:29PM -0700, Vineet Gupta wrote: > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > >> Right, so what I think Vineet is asking is if we need to disable NMIs as > >> > well, we cannot on x86 disable NMIs so no. > >> > > > The same argument works here, too: an NMI won't

Re: NMI for ARC

On 09/28/2016 03:26 PM, Andy Lutomirski wrote: >> Right, so what I think Vineet is asking is if we need to disable NMIs as >> > well, we cannot on x86 disable NMIs so no. >> > > The same argument works here, too: an NMI won't set TIF_NEED_RESCHED > without sending an IPI, so we can't miss a

Re: NMI for ARC

On 09/28/2016 03:26 PM, Andy Lutomirski wrote: >> Right, so what I think Vineet is asking is if we need to disable NMIs as >> > well, we cannot on x86 disable NMIs so no. >> > > The same argument works here, too: an NMI won't set TIF_NEED_RESCHED > without sending an IPI, so we can't miss a

Re: NMI for ARC

On Wed, Sep 28, 2016 at 3:44 PM, Vineet Gupta wrote: > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: >> 2. The low level return code, resume_user_mode_begin and/or >> resume_kernel_mode >> > > >> require interrupt safety, does that need to be NMI safe as

Re: NMI for ARC

On Wed, Sep 28, 2016 at 3:44 PM, Vineet Gupta wrote: > On 09/28/2016 03:26 PM, Andy Lutomirski wrote: >> 2. The low level return code, resume_user_mode_begin and/or >> resume_kernel_mode >> > > >> require interrupt safety, does that need to be NMI safe as well. >> > > >> We

Re: NMI for ARC

On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > 2. The low level return code, resume_user_mode_begin and/or > resume_kernel_mode > > > >> require interrupt safety, does that need to be NMI safe as well. > > > >> We ofcourse want > > > >> the very late register restore parts

Re: NMI for ARC

On 09/28/2016 03:26 PM, Andy Lutomirski wrote: > 2. The low level return code, resume_user_mode_begin and/or > resume_kernel_mode > > > >> require interrupt safety, does that need to be NMI safe as well. > > > >> We ofcourse want > > > >> the very late register restore parts

Re: NMI for ARC

On Sep 28, 2016 1:37 PM, "Peter Zijlstra" wrote: > > On Wed, Sep 28, 2016 at 12:25:11PM -0700, Andy Lutomirski wrote: > > > Yes. If the NMI returns to kernel space you must not attempt preemption > > > for reasons you found :-), > > > > Last time I looked at this, I decided

Re: NMI for ARC

On Sep 28, 2016 1:37 PM, "Peter Zijlstra" wrote: > > On Wed, Sep 28, 2016 at 12:25:11PM -0700, Andy Lutomirski wrote: > > > Yes. If the NMI returns to kernel space you must not attempt preemption > > > for reasons you found :-), > > > > Last time I looked at this, I decided that there was no

Re: NMI for ARC

On Wed, Sep 28, 2016 at 12:25:11PM -0700, Andy Lutomirski wrote: > > Yes. If the NMI returns to kernel space you must not attempt preemption > > for reasons you found :-), > > Last time I looked at this, I decided that there was no reason that > NMIs would ever need to handle preemption. Even if

Re: NMI for ARC

On Wed, Sep 28, 2016 at 12:25:11PM -0700, Andy Lutomirski wrote: > > Yes. If the NMI returns to kernel space you must not attempt preemption > > for reasons you found :-), > > Last time I looked at this, I decided that there was no reason that > NMIs would ever need to handle preemption. Even if

Re: NMI for ARC

On Wed, Sep 28, 2016 at 12:16 AM, Peter Zijlstra wrote: > On Tue, Sep 27, 2016 at 05:22:13PM -0700, Vineet Gupta wrote: > >> > Yeah, Sparc64 might be a better example, it more closely matches your >> > hardware. See >> >

Re: NMI for ARC

On Wed, Sep 28, 2016 at 12:16 AM, Peter Zijlstra wrote: > On Tue, Sep 27, 2016 at 05:22:13PM -0700, Vineet Gupta wrote: > >> > Yeah, Sparc64 might be a better example, it more closely matches your >> > hardware. See >> > arch/sparc/include/asm/irqflags_64.h:arch_local_irq_save(). >> >> So I

Re: NMI for ARC

On 09/28/2016 12:16 AM, Peter Zijlstra wrote: >> 1. Is it OK in general to short-circuit preemption off irq checks for NMI >> style >> > interrupts. > Yes. If the NMI returns to kernel space you must not attempt preemption > for reasons you found :-), if the NMI returns to userspace you should

Re: NMI for ARC

On 09/28/2016 12:16 AM, Peter Zijlstra wrote: >> 1. Is it OK in general to short-circuit preemption off irq checks for NMI >> style >> > interrupts. > Yes. If the NMI returns to kernel space you must not attempt preemption > for reasons you found :-), if the NMI returns to userspace you should

Re: NMI for ARC

On Tue, Sep 27, 2016 at 05:22:13PM -0700, Vineet Gupta wrote: > > Yeah, Sparc64 might be a better example, it more closely matches your > > hardware. See > > arch/sparc/include/asm/irqflags_64.h:arch_local_irq_save(). > > So I finally got around to doing this and as expected has turned out to be

Re: NMI for ARC

On Tue, Sep 27, 2016 at 05:22:13PM -0700, Vineet Gupta wrote: > > Yeah, Sparc64 might be a better example, it more closely matches your > > hardware. See > > arch/sparc/include/asm/irqflags_64.h:arch_local_irq_save(). > > So I finally got around to doing this and as expected has turned out to be

Re: NMI for ARC

Hi Peter, On 11/17/2015 05:15 AM, Peter Zijlstra wrote: > On Tue, Nov 17, 2015 at 06:23:21PM +0530, Vineet Gupta wrote: >> On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: >> >>> This is assuming you now have these NMIs we talked about earlier. If all >>> you have are regular IRQs this

Re: NMI for ARC

Hi Peter, On 11/17/2015 05:15 AM, Peter Zijlstra wrote: > On Tue, Nov 17, 2015 at 06:23:21PM +0530, Vineet Gupta wrote: >> On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: >> >>> This is assuming you now have these NMIs we talked about earlier. If all >>> you have are regular IRQs this

Re: NMI for ARC

On Tue, Nov 17, 2015 at 06:23:21PM +0530, Vineet Gupta wrote: > On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: > > > This is assuming you now have these NMIs we talked about earlier. If all > > you have are regular IRQs this is not possible, for we should be calling > > ->read() with

NMI for ARC

On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: > This is assuming you now have these NMIs we talked about earlier. If all > you have are regular IRQs this is not possible, for we should be calling > ->read() with IRQs disabled. > No we don't yet. The first stab at it fell flat on

NMI for ARC

On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: > This is assuming you now have these NMIs we talked about earlier. If all > you have are regular IRQs this is not possible, for we should be calling > ->read() with IRQs disabled. > No we don't yet. The first stab at it fell flat on

Re: NMI for ARC

On Tue, Nov 17, 2015 at 06:23:21PM +0530, Vineet Gupta wrote: > On Tuesday 17 November 2015 05:55 PM, Peter Zijlstra wrote: > > > This is assuming you now have these NMIs we talked about earlier. If all > > you have are regular IRQs this is not possible, for we should be calling > > ->read() with