linux-kernel - RE: [RFC] Order 4 allocation failures in the MEI client driver

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Message-ID: <PH7PR11MB76050864E8DC9F7389314BF2E58F2@PH7PR11MB7605.namprd11.prod.outlook.com>
Date: Thu, 22 Aug 2024 13:27:02 +0000
From: "Winkler, Tomas" <tomas.winkler@...el.com>
To: Arnd Bergmann <arnd@...db.de>, Rohit Agarwal <rohiagar@...omium.org>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Lubart,
 Vitaly" <vitaly.lubart@...el.com>, "Usyskin, Alexander"
	<alexander.usyskin@...el.com>
Subject: RE: [RFC] Order 4 allocation failures in the MEI client driver

> 
> On Wed, Aug 21, 2024, at 05:20, Rohit Agarwal wrote:
> > On 19/08/24 6:45 PM, Arnd Bergmann wrote:
> >> On Tue, Aug 13, 2024, at 10:45, Rohit Agarwal wrote:
> >>
> >> What is the call chain you see in the kernel messages? Is it always
> >> the same?
> > Yes the call stack is same everytime. This is the call stack
> >
> > <4>[ 2019.101352] dump_stack_lvl+0x69/0xa0 <4>[ 2019.101359]
> > warn_alloc+0x10d/0x180 <4>[ 2019.101363]
> > __alloc_pages_slowpath+0xe3d/0xe80
> > <4>[ 2019.101366] __alloc_pages+0x22f/0x2b0 <4>[ 2019.101369]
> > __kmalloc_large_node+0x9d/0x120 <4>[ 2019.101373] ?
> > mei_cl_alloc_cb+0x34/0xa0 <4>[ 2019.101377] ?
> > mei_cl_alloc_cb+0x74/0xa0 <4>[ 2019.101379] __kmalloc+0x86/0x130 <4>[
> > 2019.101382] mei_cl_alloc_cb+0x74/0xa0 <4>[ 2019.101385]
> > mei_cl_enqueue_ctrl_wr_cb+0x38/0x90
> 
> Ok, so this might be a result of mei_cl_enqueue_ctrl_wr_cb() doing
> 
>         /* for RX always allocate at least client's mtu */
>         if (length)
>                 length = max_t(size_t, length, mei_cl_mtu(cl));
> 
> which was added in 3030dc056459 ("mei: add wrapper for queuing control
> commands."). All the callers seem to be passing a short "length" of just a few
> bytes, but this would always extend it to
> cl->me_cl->props.max_msg_length in mei_cl_mtu().
> 
> Not sure where that part is set.

It's allocating maximum header for receiving buffer so it can accommodate any response. 
Looks like this part can be optimized with pre allocated buffer pool.
> 
> > <4>[ 2019.101388] mei_cl_read_start+0xb8/0x230 <4>[ 2019.101391]
> > __mei_cl_recv+0xd3/0x400 <4>[ 2019.101396] ?
> > __pfx_autoremove_wake_function+0x10/0x10
> > <4>[ 2019.101399] mei_pxp_receive_message+0x39/0x60 <4>[
> 2019.101402]
> > intel_pxp_tee_io_message+0x112/0x1e0
> > <4>[ 2019.101407] i915_pxp_ops_ioctl+0x536/0x6c0
> 
> Curiously, I don't see any evidence of i915_pxp_ops_ioctl() ever making it
> into mainline kernels, though I see some discussion about it on the mailing
> lists [1]
> 
> Do you see the same problem with a mainline kernel?
> 
> The only reference I could find to the DRM_IOCTL_I915_PXP_OPS ioctl in
> userspace seems to be in
> https://chromium.googlesource.com/chromium/src/+/a4de986102a45e29c3
> ef596f22704bdca244c26c/media/gpu/vaapi/vaapi_wrapper.cc#2004

This is chrome only mei extension for DRM. 
> 
> >> Allocating 64KB of consecutive pages repeatedly is clearly a problem
> >> at runtime, but having a single allocation during probe time is not
> >> as bad.
> > What if the length of the message is greater than 64KB, wouldn't that
> > be an issue?
> 
> That would make it an order-5 allocation.
> 
>      Arnd
> 
> 
> [1] https://patchwork.kernel.org/project/intel-
> gfx/patch/20201114014537.25495-5-sean.z.huang@...el.com/#23762967