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    SubjectRe: [PATCH] kexec: Enable runtime allocation of crash_image
    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.

    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

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