linux-kernel - Re: [PATCH] kexec: Enable runtime allocation of crash

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Message-ID: <Y4BzPDRsiPiReFLt@MiWiFi-R3L-srv>
Date:   Fri, 25 Nov 2022 15:48:12 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Ricardo Ribalda <ribalda@...omium.org>
Cc:     Eric Biederman <ebiederm@...ssion.com>,
        Philipp Rudo <prudo@...hat.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Ross Zwisler <zwisler@...nel.org>, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: Enable runtime allocation of crash_image

On 11/25/22 at 08:31am, Ricardo Ribalda wrote:
> Hi
> 
> On Fri, 25 Nov 2022 at 08:27, Baoquan He <bhe@...hat.com> wrote:
> >
> > On 11/25/22 at 06:52am, Ricardo Ribalda wrote:
> > > Hi Baoquan
> > >
> > > Thanks for your review!
> > >
> > > On Fri, 25 Nov 2022 at 03:58, Baoquan He <bhe@...hat.com> wrote:
> > > >
> > > > On 11/24/22 at 11:23pm, Ricardo Ribalda wrote:
> > > > > Usually crash_image is defined statically via the crashkernel parameter
> > > > > or DT.
> > > > >
> > > > > But if the crash kernel is not used, or is smaller than then
> > > > > area pre-allocated that memory is wasted.
> > > > >
> > > > > Also, if the crash kernel was not defined at bootime, there is no way to
> > > > > use the crash kernel.
> > > > >
> > > > > Enable runtime allocation of the crash_image if the crash_image is not
> > > > > defined statically. Following the same memory allocation/validation path
> > > > > that for the reboot kexec kernel.
> > > >
> > > > We don't check if the crashkernel memory region is valid in kernel, but
> > > > we do have done the check in kexec-tools utility. Since both kexec_load and
> > > > kexec_file_load need go through path of kexec-tools loading, we haven't
> > > > got problem with lack of the checking in kernel.
> > >
> > > Not sure if I follow you.
> > >
> > > We currently check if the crash kernel is in the right place at
> > > sanity_check_segment_list()
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/kernel/kexec_core.c#n239
> >
> > And it's not checking if crashkernel memory is valid in
> > sanity_check_segment_list(), right? It's checking if the segments
> > are placed correctly.
> 
> If it is not valid, then this condition is not met.

Yeah. BUT, even though it's valid, below condition could not be met
either. They are not the same thing. 

> 
> /* Ensure we are within the crash kernel limits */
> if ((mstart < phys_to_boot_phys(crashk_res.start)) ||
>     (mend > phys_to_boot_phys(crashk_res.end)))
>           return -EADDRNOTAVAIL;
> 
> 
> >
> 
> 
> -- 
> Ricardo Ribalda
>