linux-kernel - Re: [PATCH] resource,kexec: walk_system_ram_res

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Message-ID: <ZxJbOinZ0E4Ppmak@smile.fi.intel.com>
Date: Fri, 18 Oct 2024 15:57:30 +0300
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Gregory Price <gourry@...rry.net>
Cc: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org, bhelgaas@...gle.com,
	ilpo.jarvinen@...ux.intel.com, mika.westerberg@...ux.intel.com,
	ying.huang@...el.com, bhe@...hat.com, tglx@...utronix.de,
	takahiro.akashi@...aro.org, stable@...r.kernel.org
Subject: Re: [PATCH] resource,kexec: walk_system_ram_res_rev must retain
 resource flags

On Thu, Oct 17, 2024 at 03:03:47PM -0400, Gregory Price wrote:
> walk_system_ram_res_rev() erroneously discards resource flags when
> passing the information to the callback.
> 
> This causes systems with IORESOURCE_SYSRAM_DRIVER_MANAGED memory to
> have these resources selected during kexec to store kexec buffers
> if that memory happens to be at placed above normal system ram.
> 
> This leads to undefined behavior after reboot. If the kexec buffer
> is never touched, nothing happens. If the kexec buffer is touched,
> it could lead to a crash (like below) or undefined behavior.
> 
> Tested on a system with CXL memory expanders with driver managed
> memory, TPM enabled, and CONFIG_IMA_KEXEC=y. Adding printk's
> showed the flags were being discarded and as a result the check
> for IORESOURCE_SYSRAM_DRIVER_MANAGED passes.
> 
> find_next_iomem_res: name(System RAM (kmem))
> 		     start(10000000000)
> 		     end(1034fffffff)
> 		     flags(83000200)
> 
> locate_mem_hole_top_down: start(10000000000) end(1034fffffff) flags(0)
> 
> [.] BUG: unable to handle page fault for address: ffff89834ffff000

Please, cut this down to only important ~3-5 lines as suggested in
the Submitting Patches documentation.

Yeah, I see that Andrew applied it to hist testing branch, if it's not going to
be updated there, consider above as a hint for the future contributions with
backtraces.

-- 
With Best Regards,
Andy Shevchenko