linux-kernel - RE: [char-misc-next] mei: use kvmalloc for read buffer

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Message-ID: <CY5PR11MB636626DB1AB4507D847E21CEED442@CY5PR11MB6366.namprd11.prod.outlook.com>
Date: Mon, 14 Oct 2024 13:15:49 +0000
From: "Usyskin, Alexander" <alexander.usyskin@...el.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: "Weil, Oren jer" <oren.jer.weil@...el.com>, Tomas Winkler
	<tomasw@...il.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [char-misc-next] mei: use kvmalloc for read buffer

> -----Original Message-----
> From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Sent: Sunday, October 13, 2024 6:08 PM
> To: Usyskin, Alexander <alexander.usyskin@...el.com>
> Cc: Weil, Oren jer <oren.jer.weil@...el.com>; Tomas Winkler
> <tomasw@...il.com>; linux-kernel@...r.kernel.org
> Subject: Re: [char-misc-next] mei: use kvmalloc for read buffer
> 
> On Sun, Oct 13, 2024 at 02:22:27PM +0000, Usyskin, Alexander wrote:
> > > -----Original Message-----
> > > From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Sent: Sunday, October 13, 2024 3:14 PM
> > > To: Usyskin, Alexander <alexander.usyskin@...el.com>
> > > Cc: Weil, Oren jer <oren.jer.weil@...el.com>; Tomas Winkler
> > > <tomasw@...il.com>; linux-kernel@...r.kernel.org
> > > Subject: Re: [char-misc-next] mei: use kvmalloc for read buffer
> > >
> > > On Sun, Oct 13, 2024 at 02:53:14PM +0300, Alexander Usyskin wrote:
> > > > Read buffer is allocated according to max message size,
> > > > reported by the firmware and may reach 64K in systems
> > > > with pxp client.
> > > > Contiguous 64k allocation may fail under memory pressure.
> > > > Read buffer is used as in-driver message storage and
> > > > not required to be contiguous.
> > > > Use kvmalloc to allow kernel to allocate non-contiguous
> > > > memory in this case.
> > > >
> > > > Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
> > > > ---
> > > >  drivers/misc/mei/client.c | 4 ++--
> > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > What about this thread:
> > > 	https://lore.kernel.org/all/20240813084542.2921300-1-
> > > rohiagar@...omium.org/

[1] https://lore.kernel.org/all/20240813084542.2921300-1-rohiagar@chromium.org/
> > >
> > > No attribution for the reporter?  Does it solve their problem?
> > >
> > This patch is a result from non-public bug report on ChromeOS.
> 
> Then make that bug report public as it was discussed in public already :)
> 
Unfortunately, it is not my call.
For now, I'll anchor this on [1]

> > > Also, where is this memory pressure coming from, what is the root cause
> > > and what commit does this fix?  Stable backports needed?  Anything else?
> > >
> > The ChromeOS is extremely short on memory by design and can trigger
> > this situation very easily.
> 
> So normal allocations are failing?  That feels wrong, what caused this?

64K is order 4 allocation and may fail according to [1].

> > I do not think that this patch fixes any commit - the problematic code exists
> > from the earliest versions of this driver.
> > As this problem reproduced only on ChromeOS I believe that no need
> > in wide backport, the ChromeOS can cherry-pick the patch.
> > From your experience, is this the right strategy?
> 
> No.

Sure, I'll use
Fixes: 3030dc056459 ("mei: add wrapper for queuing control commands.")
where the first time such buffer allocated and add stable here in v2.

- - 
Thanks,
Sasha