linux-kernel - Re: [PATCH v2] x86, espfix: init espfix on the boot cpu side

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Date:	Mon, 29 Jun 2015 08:48:59 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Zhu Guihua <zhugh.fnst@...fujitsu.com>, hpa@...or.com,
	linux-kernel@...r.kernel.org, luto@...capital.net, luto@...nel.org,
	tglx@...utronix.de, x86@...nel.org
Subject: Re: [PATCH v2] x86, espfix: init espfix on the boot cpu side


* Borislav Petkov <bp@...en8.de> wrote:

> On Fri, Jun 26, 2015 at 05:33:22PM +0800, Zhu Guihua wrote:
> > The following lockdep warning occurrs when running with latest kernel:
> > [    3.178000] ------------[ cut here ]------------
> > [    3.183000] WARNING: CPU: 128 PID: 0 at kernel/locking/lockdep.c:2755 lockdep_trace_alloc+0xdd/0xe0()
> > [    3.193000] DEBUG_LOCKS_WARN_ON(irqs_disabled_flags(flags))
> > [    3.199000] Modules linked in:
> > 
> > [    3.203000] CPU: 128 PID: 0 Comm: swapper/128 Not tainted 4.1.0-rc3 #70
> > [    3.221000]  0000000000000000 2d6601fb3e6d4e4c ffff88086fd5fc38 ffffffff81773f0a
> > [    3.230000]  0000000000000000 ffff88086fd5fc90 ffff88086fd5fc78 ffffffff8108c85a
> > [    3.238000]  ffff88086fd60000 0000000000000092 ffff88086fd60000 00000000000000d0
> > [    3.246000] Call Trace:
> > [    3.249000]  [<ffffffff81773f0a>] dump_stack+0x4c/0x65
> > [    3.255000]  [<ffffffff8108c85a>] warn_slowpath_common+0x8a/0xc0
> > [    3.261000]  [<ffffffff8108c8e5>] warn_slowpath_fmt+0x55/0x70
> > [    3.268000]  [<ffffffff810ee24d>] lockdep_trace_alloc+0xdd/0xe0
> > [    3.274000]  [<ffffffff811cda0d>] __alloc_pages_nodemask+0xad/0xca0
> > [    3.281000]  [<ffffffff810ec7ad>] ? __lock_acquire+0xf6d/0x1560
> > [    3.288000]  [<ffffffff81219c8a>] alloc_page_interleave+0x3a/0x90
> > [    3.295000]  [<ffffffff8121b32d>] alloc_pages_current+0x17d/0x1a0
> > [    3.301000]  [<ffffffff811c869e>] ? __get_free_pages+0xe/0x50
> > [    3.308000]  [<ffffffff811c869e>] __get_free_pages+0xe/0x50
> > [    3.314000]  [<ffffffff8102640b>] init_espfix_ap+0x17b/0x320
> > [    3.320000]  [<ffffffff8105c691>] start_secondary+0xf1/0x1f0
> > [    3.327000] ---[ end trace 1b3327d9d6a1d62c ]---
> > 
> > As we alloc pages with GFP_KERNEL in init_espfix_ap() which is called
> > before enabled local irq, and the lockdep sub-system considers this
> > behaviour as allocating memory with GFP_FS with local irq disabled,
> > then trigger the warning as mentioned about.
> > 
> > So we allocate them on the boot CPU side when the target CPU is bringing
> > up by the primary CPU, and hand them over to the secondary CPU.
> > 
> > Signed-off-by: Zhu Guihua <zhugh.fnst@...fujitsu.com>
> > ---
> > v2:
> >  -allocate espfix stack pages when the targert CPU is bringing up by the
> >   primary CPU
> >  -commit messages changed
> > v1:
> >  -Alloc the page on the node the target CPU is on.
> > RFC v2:
> >  -Let the boot up routine init the espfix stack for the target cpu after it
> >   booted.
> 
> Looks ok to me and it works on the 16-node NUMA guest I was triggering the splat
> with.
> 
> hpa, is that what you had in mind?

Looks good to me, but please split it into two parts: one that pushes down the CPU 
index - another that does the actual change.

Should this break anything then being in two parts will make it much easier to 
bisect to.

Thanks,

	Ingo
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