linux-kernel - Re: [PATCH RFC V3 6/9] x86/entry: Pass irqentry_state

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Date:   Sun, 18 Oct 2020 22:37:36 -0700
From:   Ira Weiny <ira.weiny@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>, x86@...nel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC V3 6/9] x86/entry: Pass irqentry_state_t by reference

On Fri, Oct 16, 2020 at 02:55:21PM +0200, Thomas Gleixner wrote:
> On Fri, Oct 16 2020 at 13:45, Peter Zijlstra wrote:
> > On Fri, Oct 09, 2020 at 12:42:55PM -0700, ira.weiny@...el.com wrote:
> >> @@ -238,7 +236,7 @@ noinstr void idtentry_exit_nmi(struct pt_regs *regs, bool restore)
> >>  
> >>  	rcu_nmi_exit();
> >>  	lockdep_hardirq_exit();
> >> -	if (restore)
> >> +	if (irq_state->exit_rcu)
> >>  		lockdep_hardirqs_on(CALLER_ADDR0);
> >>  	__nmi_exit();
> >>  }
> >
> > That's not nice.. The NMI path is different from the IRQ path and has a
> > different variable. Yes, this works, but *groan*.
> >
> > Maybe union them if you want to avoid bloating the structure, but the
> > above makes it really hard to read.
> 
> Right, and also that nmi entry thing should not be in x86. Something
> like the untested below as first cleanup.

Ok, I see what Peter was talking about.  I've added this patch to the series.

> 
> Thanks,
> 
>         tglx
> ----
> Subject: x86/entry: Move nmi entry/exit into common code
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Fri, 11 Sep 2020 10:09:56 +0200
> 
> Add blurb here.

How about:

To prepare for saving PKRS values across NMI's we lift the
idtentry_[enter|exit]_nmi() to the common code.  Rename them to
irqentry_nmi_[enter|exit]() to reflect the new generic nature and store the
state in the same irqentry_state_t structure as the other irqentry_*()
functions.  Finally, differentiate the state being stored between the NMI and
IRQ path by adding 'lockdep' to irqentry_state_t.

?

> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/entry/common.c         |   34 ----------------------------------
>  arch/x86/include/asm/idtentry.h |    3 ---
>  arch/x86/kernel/cpu/mce/core.c  |    6 +++---
>  arch/x86/kernel/nmi.c           |    6 +++---
>  arch/x86/kernel/traps.c         |   13 +++++++------
>  include/linux/entry-common.h    |   20 ++++++++++++++++++++
>  kernel/entry/common.c           |   36 ++++++++++++++++++++++++++++++++++++
>  7 files changed, 69 insertions(+), 49 deletions(-)
> 

[snip]

> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -343,6 +343,7 @@ void irqentry_exit_to_user_mode(struct p
>  #ifndef irqentry_state
>  typedef struct irqentry_state {
>  	bool	exit_rcu;
> +	bool	lockdep;
>  } irqentry_state_t;

Building on what Peter said do you agree this should be made into a union?

It may not be strictly necessary in this patch but I think it would reflect the
mutual exclusivity better and could be changed easy enough in the follow on
patch which adds the pkrs state.

Ira