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Date:   Fri, 25 Nov 2022 17:27:09 +0800
From:   Baoquan He <bhe@redhat.com>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Eric Biederman <ebiederm@xmission.com>,
        Philipp Rudo <prudo@redhat.com>,
        Sergey Senozhatsky <senozhatsky@chromium.org>,
        Ross Zwisler <zwisler@kernel.org>, kexec@lists.infradead.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] kexec: Enable runtime allocation of crash_image
Message-ID: <Y4CKbTxycyW3rxKe@MiWiFi-R3L-srv>
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On 11/25/22 at 09:10am, Ricardo Ribalda wrote:
> Hi Baoquan
> 
> On Fri, 25 Nov 2022 at 08:45, Baoquan He <bhe@redhat.com> wrote:
> >
> > On 11/25/22 at 08:26am, Ricardo Ribalda wrote:
> > > Hi Baoquan
> > >
> > > On Fri, 25 Nov 2022 at 08:15, Baoquan He <bhe@redhat.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@redhat.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
> > > >
> > > > Please check below code in kexec-tools utility, currently we have to use
> > > > kexec -p to enter into kexec_load or kexec_file_load system call. Before
> > > > entering system call, we have below code:
> > >
> > > So your concern is that the current kexec-tools does not let you pass
> > > a crashkernel unless there is memory reserved for it?
> >
> > No, my concern is why we have to do the check in kernel if we have done
> > that in kexec-tools utility. You didn't say your kexec-lite need this
> > until now. I think it's fine to add the check in kernel if you prefer to
> > do the check in kernel, but not in kexec-lite.
> >
> > The motivation or reason you want to make the change is very important.
> 
> kexec-lite is just to test the kernel code. It is easier to follow
> than kexec-utils and supports 32bit userspace on a 64bit kernel.
> 
> 
> I think it was clear. The motivation is to enable the use of
> crashkernel when it is not statically predefined.

I thought you are adding a check on crashkernel region validation. Now I
am totally lost how this patch can enable the use of crashkernel. I will
wait a while to see if other people understand it.

> 
> Any suggestions on how I can make it more clear?
> 
> 
> 
> >
> >
> > >
> > > Once the changes land in the kernel I can make a patch for that. I am
> > > currently using this to test the code:
> > >
> > > https://chromium-review.googlesource.com/c/chromiumos/platform2/+/3953579/4/kexec-lite/kexec-lite.c
> > >
> > > >
> > > > https://kernel.googlesource.com/pub/scm/utils/kernel/kexec/kexec-tools.git/+/refs/heads/master/kexec/kexec.c
> > > >
> > > > int main(int argc, char *argv[])
> > > > {
> > > > ......
> > > >                 if (do_load &&
> > > >             ((kexec_flags & KEXEC_ON_CRASH) ||
> > > >              (kexec_file_flags & KEXEC_FILE_ON_CRASH)) &&
> > > >             !is_crashkernel_mem_reserved()) {
> > > >                 die("Memory for crashkernel is not reserved\n"
> > > >                     "Please reserve memory by passing"
> > > >                     "\"crashkernel=Y@X\" parameter to kernel\n"
> > > >                     "Then try to loading kdump kernel\n");
> 
> Having that check ALSO is unserspace is fine. It lets kexec show a
> more meaningful error message. But we should not rely on userspace
> checks.
> 
> This patch is not about adding an extra check on the kernel, but to
> enable extra functionaliry.
> 
> > > >         }
> > > >
> > > > ......
> > > > }
> > > >
> > > > >
> > > > >
> > > > > >
> > > > > > However, even though we want to do the check, doing like below is much
> > > > > > easier and more reasonable.
> > > > > >
> > > > > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > > > > > index 45637511e0de..4d1339bd2ccf 100644
> > > > > > --- a/kernel/kexec_file.c
> > > > > > +++ b/kernel/kexec_file.c
> > > > > > @@ -344,6 +344,8 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
> > > > > >
> > > > > >         dest_image = &kexec_image;
> > > > > >         if (flags & KEXEC_FILE_ON_CRASH) {
> > > > > > +               if (!crash_memory_valid())
> > > > > > +                       return -EINVAL;
> > > > > >                 dest_image = &kexec_crash_image;
> > > > > >                 if (kexec_crash_image)
> > > > > >                         arch_kexec_unprotect_crashkres();
> > > > > >
> > > > > > So, I am wondering if there is an issue encountered if we don't do the
> > > > > > check in kernel.
> > > > > >
> > > > > > Thanks
> > > > > > Baoquan
> > > > > >
> > > > > > >
> > > > > > > ---
> > > > > > >
> > > > > > > To: Eric Biederman <ebiederm@xmission.com>
> > > > > > > Cc: kexec@lists.infradead.org
> > > > > > > Cc: linux-kernel@vger.kernel.org
> > > > > > > Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
> > > > > > > Cc: linux-kernel@vger.kernel.org
> > > > > > > Cc: Ross Zwisler <zwisler@kernel.org>
> > > > > > > Cc: Philipp Rudo <prudo@redhat.com>
> > > > > > > Cc: Baoquan He <bhe@redhat.com>
> > > > > > > ---
> > > > > > >  include/linux/kexec.h | 1 +
> > > > > > >  kernel/kexec.c        | 9 +++++----
> > > > > > >  kernel/kexec_core.c   | 5 +++++
> > > > > > >  kernel/kexec_file.c   | 7 ++++---
> > > > > > >  4 files changed, 15 insertions(+), 7 deletions(-)
> > > > > > >
> > > > > > > diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> > > > > > > index 41a686996aaa..98ca9a32bc8e 100644
> > > > > > > --- a/include/linux/kexec.h
> > > > > > > +++ b/include/linux/kexec.h
> > > > > > > @@ -427,6 +427,7 @@ extern int kexec_load_disabled;
> > > > > > >  extern bool kexec_in_progress;
> > > > > > >
> > > > > > >  int crash_shrink_memory(unsigned long new_size);
> > > > > > > +bool __crash_memory_valid(void);
> > > > > > >  ssize_t crash_get_memory_size(void);
> > > > > > >
> > > > > > >  #ifndef arch_kexec_protect_crashkres
> > > > > > > diff --git a/kernel/kexec.c b/kernel/kexec.c
> > > > > > > index cb8e6e6f983c..b5c17db25e88 100644
> > > > > > > --- a/kernel/kexec.c
> > > > > > > +++ b/kernel/kexec.c
> > > > > > > @@ -28,7 +28,7 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
> > > > > > >       struct kimage *image;
> > > > > > >       bool kexec_on_panic = flags & KEXEC_ON_CRASH;
> > > > > > >
> > > > > > > -     if (kexec_on_panic) {
> > > > > > > +     if (kexec_on_panic && __crash_memory_valid()) {
> > > > > > >               /* Verify we have a valid entry point */
> > > > > > >               if ((entry < phys_to_boot_phys(crashk_res.start)) ||
> > > > > > >                   (entry > phys_to_boot_phys(crashk_res.end)))
> > > > > > > @@ -44,7 +44,7 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
> > > > > > >       image->nr_segments = nr_segments;
> > > > > > >       memcpy(image->segment, segments, nr_segments * sizeof(*segments));
> > > > > > >
> > > > > > > -     if (kexec_on_panic) {
> > > > > > > +     if (kexec_on_panic && __crash_memory_valid()) {
> > > > > > >               /* Enable special crash kernel control page alloc policy. */
> > > > > > >               image->control_page = crashk_res.start;
> > > > > > >               image->type = KEXEC_TYPE_CRASH;
> > > > > > > @@ -101,7 +101,7 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
> > > > > > >
> > > > > > >       if (flags & KEXEC_ON_CRASH) {
> > > > > > >               dest_image = &kexec_crash_image;
> > > > > > > -             if (kexec_crash_image)
> > > > > > > +             if (kexec_crash_image && __crash_memory_valid())
> > > > > > >                       arch_kexec_unprotect_crashkres();
> > > > > > >       } else {
> > > > > > >               dest_image = &kexec_image;
> > > > > > > @@ -157,7 +157,8 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
> > > > > > >       image = xchg(dest_image, image);
> > > > > > >
> > > > > > >  out:
> > > > > > > -     if ((flags & KEXEC_ON_CRASH) && kexec_crash_image)
> > > > > > > +     if ((flags & KEXEC_ON_CRASH) && kexec_crash_image &&
> > > > > > > +         __crash_memory_valid())
> > > > > > >               arch_kexec_protect_crashkres();
> > > > > > >
> > > > > > >       kimage_free(image);
> > > > > > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> > > > > > > index ca2743f9c634..77083c9760fb 100644
> > > > > > > --- a/kernel/kexec_core.c
> > > > > > > +++ b/kernel/kexec_core.c
> > > > > > > @@ -1004,6 +1004,11 @@ void crash_kexec(struct pt_regs *regs)
> > > > > > >       }
> > > > > > >  }
> > > > > > >
> > > > > > > +bool __crash_memory_valid(void)
> > > > > > > +{
> > > > > > > +     return crashk_res.end != crashk_res.start;
> > > > > > > +}
> > > > > > > +
> > > > > > >  ssize_t crash_get_memory_size(void)
> > > > > > >  {
> > > > > > >       ssize_t size = 0;
> > > > > > > diff --git a/kernel/kexec_file.c b/kernel/kexec_file.c
> > > > > > > index 45637511e0de..0671f4f370ff 100644
> > > > > > > --- a/kernel/kexec_file.c
> > > > > > > +++ b/kernel/kexec_file.c
> > > > > > > @@ -280,7 +280,7 @@ kimage_file_alloc_init(struct kimage **rimage, int kernel_fd,
> > > > > > >
> > > > > > >       image->file_mode = 1;
> > > > > > >
> > > > > > > -     if (kexec_on_panic) {
> > > > > > > +     if (kexec_on_panic && __crash_memory_valid()) {
> > > > > > >               /* Enable special crash kernel control page alloc policy. */
> > > > > > >               image->control_page = crashk_res.start;
> > > > > > >               image->type = KEXEC_TYPE_CRASH;
> > > > > > > @@ -345,7 +345,7 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
> > > > > > >       dest_image = &kexec_image;
> > > > > > >       if (flags & KEXEC_FILE_ON_CRASH) {
> > > > > > >               dest_image = &kexec_crash_image;
> > > > > > > -             if (kexec_crash_image)
> > > > > > > +             if (kexec_crash_image && __crash_memory_valid())
> > > > > > >                       arch_kexec_unprotect_crashkres();
> > > > > > >       }
> > > > > > >
> > > > > > > @@ -408,7 +408,8 @@ SYSCALL_DEFINE5(kexec_file_load, int, kernel_fd, int, initrd_fd,
> > > > > > >  exchange:
> > > > > > >       image = xchg(dest_image, image);
> > > > > > >  out:
> > > > > > > -     if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image)
> > > > > > > +     if ((flags & KEXEC_FILE_ON_CRASH) && kexec_crash_image &&
> > > > > > > +         __crash_memory_valid())
> > > > > > >               arch_kexec_protect_crashkres();
> > > > > > >
> > > > > > >       kexec_unlock();
> > > > > > >
> > > > > > > ---
> > > > > > > base-commit: 4312098baf37ee17a8350725e6e0d0e8590252d4
> > > > > > > change-id: 20221124-kexec-noalloc-3cab3cbe000f
> > > > > > >
> > > > > > > Best regards,
> > > > > > > --
> > > > > > > Ricardo Ribalda <ribalda@chromium.org>
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > > > --
> > > > > Ricardo Ribalda
> > > > >
> > > >
> > >
> > >
> > > --
> > > Ricardo Ribalda
> > >
> >
> 
> 
> -- 
> Ricardo Ribalda
>