[PATCH 1/2] x86/kexec: Use up-to-dated screen_info copy to fill boot params
decui at microsoft.com
Mon Nov 16 22:39:44 EST 2020
> From: Kairui Song <kasong at redhat.com>
> Sent: Wednesday, October 14, 2020 2:24 AM
> To: linux-kernel at vger.kernel.org
> kexec_file_load now just reuse the old boot_params.screen_info.
> But if drivers have change the hardware state, boot_param.screen_info
> could contain invalid info.
> For example, the video type might be no longer VGA, or frame buffer
> address changed. If kexec kernel keep using the old screen_info,
> kexec'ed kernel may attempt to write to an invalid framebuffer
> memory region.
> There are two screen_info globally available, boot_params.screen_info
> and screen_info. Later one is a copy, and could be updated by drivers.
> So let kexec_file_load use the updated copy.
> Signed-off-by: Kairui Song <kasong at redhat.com>
> arch/x86/kernel/kexec-bzimage64.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
> diff --git a/arch/x86/kernel/kexec-bzimage64.c
> index 57c2ecf43134..ce831f9448e7 100644
> --- a/arch/x86/kernel/kexec-bzimage64.c
> +++ b/arch/x86/kernel/kexec-bzimage64.c
> @@ -200,8 +200,7 @@ setup_boot_parameters(struct kimage *image, struct
> boot_params *params,
> params->hdr.hardware_subarch = boot_params.hdr.hardware_subarch;
> /* Copying screen_info will do? */
> - memcpy(¶ms->screen_info, &boot_params.screen_info,
> - sizeof(struct screen_info));
> + memcpy(¶ms->screen_info, &screen_info, sizeof(struct screen_info));
> /* Fill in memsize later */
> params->screen_info.ext_mem_k = 0;
According to "man kexec", kdump/kexec can use 2 different syscalls to set up the
Specify that the new KEXEC_FILE_LOAD syscall should be used exclusively.
Specify that the old KEXEC_LOAD syscall should be used exclusively (the default).
It looks I can only reproduce the call-trace
(https://bugzilla.redhat.com/show_bug.cgi?id=1867887#c5) with KEXEC_FILE_LOAD:
I did kdump tests in Ubuntu 20.04 VM and by default the VM used the KEXEC_LOAD
syscall and I couldn't reproduce the call-trace; after I added the "-s" parameter to use
the KEXEC_FILE_LOAD syscall, I could reproduce the call-trace and I can confirm your
patch can eliminate the call-trace because the "efifb" driver doesn't even load with
Your patch is only for the KEXEC_FILE_LOAD syscall, and I'm sure it's not used in the
code path of the KEXEC_LOAD syscall.
So, in the case of the KEXEC_LOAD syscall, do you know how the *kexec* kernel's
boot_params.screen_info.lfb_base is intialized? I haven't figured it out yet.
More information about the kexec