linux-kernel - Re: [PATCH v2 1/2] kexec: Add KEXEC_FILE_NO

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Message-ID: <A39EA0B7-F7C3-49DE-9A35-4CF2A5E49DEE@juniper.net>
Date: Thu, 21 Aug 2025 16:22:29 +0000
From: Brian Mak <makb@...iper.net>
To: Andrew Morton <akpm@...ux-foundation.org>
CC: Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Alexander
 Graf <graf@...zon.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen
	<dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Rob Herring
	<robh@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "x86@...nel.org"
	<x86@...nel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] kexec: Add KEXEC_FILE_NO_CMA as a legal flag

On Aug 20, 2025, at 9:47 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:

> On Tue, 5 Aug 2025 14:15:26 -0700 Brian Mak <makb@...iper.net> wrote:
> 
>> Commit 07d24902977e ("kexec: enable CMA based contiguous allocation")
>> introduces logic to use CMA-based allocation in kexec by default. As
>> part of the changes, it introduces a kexec_file_load flag to disable the
>> use of CMA allocations from userspace. However, this flag is broken
>> since it is missing from the list of legal flags for kexec_file_load.
>> kexec_file_load returns EINVAL when attempting to use the flag.
>> 
>> Fix this by adding the KEXEC_FILE_NO_CMA flag to the list of legal flags
>> for kexec_file_load.
>> 
>> Fixes: 07d24902977e ("kexec: enable CMA based contiguous allocation")
> 
> A description of the userspace-visible runtime effects of this bug
> would be very helpful, please.  A lot more than "is broken"!

Hi Andrew,

Thanks for your comment. The userspace-visible runtime effect of this
bug is that kexec_file_load returns EINVAL when attempting to use the
KEXEC_FILE_NO_CMA flag. This is stated in the sentence following the
"this flag is broken" statement.

Is there something else that you wanted me to add here?

Thanks,
Brian