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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
	Sean Christopherson <sean.j.christopherson@intel.com>
Subject: Re: [patch V2 20/29] x86/dumpstack/64: Speedup in_exception_stack()
Date: Fri, 5 Apr 2019 16:55:20 -0500	[thread overview]
Message-ID: <20190405215520.wsevtopb63oetkfd@treble> (raw)
In-Reply-To: <20190405150930.219316964@linutronix.de>

On Fri, Apr 05, 2019 at 05:07:18PM +0200, Thomas Gleixner wrote:
> The current implementation of in_exception_stack() iterates over the
> exception stacks array. Most of the time this is an useless exercise, but
> even for the actual use cases (perf and ftrace) it takes at least 2
> iterations to get to the NMI stack.
> 
> As the exception stacks and the guard pages are page aligned the loop can
> be avoided completely.
> 
> Add a initial check whether the stack pointer is inside the full exception
> stack area and leave early if not.
> 
> Create a lookup table which describes the stack area. The table index is
> the page offset from the beginning of the exception stacks. So for any
> given stack pointer the page offset is computed and a lookup in the
> description table is performed. If it is inside a guard page, return. If
> not, use the descriptor to fill in the info structure.
> 
> The table is filled at compile time and for the !KASAN case the interesting
> page descriptors exactly fit into a single cache line. Just the last guard
> page descriptor is in the next cacheline, but that should not be accessed
> in the regular case.
> 
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> ---
> V2: Simplify the macro maze

This is indeed a little better.  It's friday, have an ack.

Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>

I don't like the clever ISTACK_* macro naming however...

-- 
Josh

  reply	other threads:[~2019-04-05 21:55 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-05 15:06 [patch V2 00/29] x86: Add guard pages to exception and interrupt stacks Thomas Gleixner
2019-04-05 15:06 ` [patch V2 01/29] x86/irq/64: Limit IST stack overflow check to #DB stack Thomas Gleixner
2019-04-05 15:07 ` [patch V2 02/29] x86/dumpstack: Fix off-by-one errors in stack identification Thomas Gleixner
2019-04-05 15:44   ` Sean Christopherson
2019-04-05 15:07 ` [patch V2 03/29] x86/irq/64: Remove a hardcoded irq_stack_union access Thomas Gleixner
2019-04-05 16:37   ` Sean Christopherson
2019-04-05 16:38     ` Sean Christopherson
2019-04-05 17:18     ` Josh Poimboeuf
2019-04-05 17:47       ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 04/29] x86/irq/64: Sanitize the top/bottom confusion Thomas Gleixner
2019-04-05 16:54   ` Sean Christopherson
2019-04-05 15:07 ` [patch V2 05/29] x86/idt: Remove unused macro SISTG Thomas Gleixner
2019-04-05 15:07 ` [patch V2 06/29] x86/exceptions: Remove unused stack defines on 32bit Thomas Gleixner
2019-04-05 15:07 ` [patch V2 07/29] x86/exceptions: Make IST index zero based Thomas Gleixner
2019-04-05 18:59   ` Sean Christopherson
2019-04-05 15:07 ` [patch V2 08/29] x86/cpu_entry_area: Cleanup setup functions Thomas Gleixner
2019-04-05 19:25   ` Sean Christopherson
2019-04-05 15:07 ` [patch V2 09/29] x86/exceptions: Add structs for exception stacks Thomas Gleixner
2019-04-05 20:48   ` Sean Christopherson
2019-04-05 20:50     ` Sean Christopherson
2019-04-05 21:00     ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 10/29] x86/cpu_entry_area: Prepare for IST guard pages Thomas Gleixner
2019-04-05 15:07 ` [patch V2 11/29] x86/cpu_entry_area: Provide exception stack accessor Thomas Gleixner
2019-04-05 15:07 ` [patch V2 12/29] x86/traps: Use cpu_entry_area instead of orig_ist Thomas Gleixner
2019-04-05 15:07 ` [patch V2 13/29] x86/irq/64: Use cpu entry area " Thomas Gleixner
2019-04-05 15:07 ` [patch V2 14/29] x86/dumpstack/64: Use cpu_entry_area " Thomas Gleixner
2019-04-05 15:07 ` [patch V2 15/29] x86/cpu: Prepare TSS.IST setup for guard pages Thomas Gleixner
2019-04-05 15:07 ` [patch V2 16/29] x86/cpu: Remove orig_ist array Thomas Gleixner
2019-04-05 15:07 ` [patch V2 17/29] x86/exceptions: Disconnect IST index and stack order Thomas Gleixner
2019-04-05 21:57   ` Josh Poimboeuf
2019-04-05 22:00     ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 18/29] x86/exceptions: Enable IST guard pages Thomas Gleixner
2019-04-05 15:07 ` [patch V2 19/29] x86/exceptions: Split debug IST stack Thomas Gleixner
2019-04-05 20:55   ` Sean Christopherson
2019-04-05 21:01     ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 20/29] x86/dumpstack/64: Speedup in_exception_stack() Thomas Gleixner
2019-04-05 21:55   ` Josh Poimboeuf [this message]
2019-04-05 21:56     ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 21/29] x86/irq/32: Define IRQ_STACK_SIZE Thomas Gleixner
2019-04-05 15:07 ` [patch V2 22/29] x86/irq/32: Make irq stack a character array Thomas Gleixner
2019-04-05 15:07 ` [patch V2 23/29] x86/irq/32: Rename hard/softirq_stack to hard/softirq_stack_ptr Thomas Gleixner
2019-04-05 15:07 ` [patch V2 24/29] x86/irq/64: Rename irq_stack_ptr to hardirq_stack_ptr Thomas Gleixner
2019-04-05 15:07 ` [patch V2 25/29] x86/irq/32: Invoke irq_ctx_init() from init_IRQ() Thomas Gleixner
2019-04-05 15:27   ` Juergen Gross
2019-04-05 15:07 ` [patch V2 26/29] x86/irq/32: Handle irq stack allocation failure proper Thomas Gleixner
2019-04-05 15:07 ` [patch V2 27/29] x86/irq/64: Split the IRQ stack into its own pages Thomas Gleixner
2019-04-05 15:07 ` [patch V2 28/29] x86/irq/64: Remap the IRQ stack with guard pages Thomas Gleixner
2019-04-07  4:56   ` Andy Lutomirski
2019-04-07  6:08     ` Thomas Gleixner
2019-04-07  9:28       ` Andy Lutomirski
2019-04-07  9:34         ` Thomas Gleixner
2019-04-07 14:03           ` Andy Lutomirski
2019-04-07 22:44     ` Thomas Gleixner
2019-04-08  2:23       ` Andy Lutomirski
2019-04-08  6:46         ` Thomas Gleixner
2019-04-08 16:18           ` Andy Lutomirski
2019-04-08 16:36             ` Josh Poimboeuf
2019-04-08 16:44             ` Thomas Gleixner
2019-04-08 18:19               ` Thomas Gleixner
2019-04-05 15:07 ` [patch V2 29/29] x86/irq/64: Remove stack overflow debug code Thomas Gleixner

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