On Thu, Oct 17, 2019 at 05:43:45PM +0800, Lianbo Jiang wrote: > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204793 Put that as a Link: below. > Kdump kernel will reuse the first 640k region because of some reasons, s/ of some reasons// > for example: the trampline and conventional PC system BIOS region may spellcheck: s/trampline/trampoline/ I see two more typos in here and if you had a spellchecker enabled in your editor where you write the commit message, you'll see them too. Please use one. > require to allocate memory in this area. Obviously, kdump kernel will > also overwrite the first 640k region, Well, it is not obvious to me. Please be more specific: why would the kdump kernel do that? > therefore, kernel has to copy > the contents of the first 640k area to a backup area, which is done in > purgatory(), because vmcore may need the old memory. When vmcore is > dumped, kdump kernel will read the old memory from the backup area of > the first 640k area. > > Basically, the main reason should be clear, kernel does not correctly > handle the first 640k region when SME is active, If you mention the actual reason here, that sentence would be clearer: "When SME is enabled in the first kernel, the kdump kernel must access the first kernel's memory with the encryption bit set." Something like that. > which causes that > kernel does not properly copy these old memory to the backup area in > purgatory(). Therefore, kdump kernel reads out the incorrect contents s/incorrect/encrypted/ > from the backup area when dumping vmcore. Finally, the phenomenon is phenomenon? > as follow: > > [root linux]$ crash vmlinux /var/crash/127.0.0.1-2019-09-19-08\:31\:27/vmcore > WARNING: kernel relocated [240MB]: patching 97110 gdb minimal_symbol values > > KERNEL: /var/crash/127.0.0.1-2019-09-19-08:31:27/vmlinux > DUMPFILE: /var/crash/127.0.0.1-2019-09-19-08:31:27/vmcore [PARTIAL DUMP] > CPUS: 128 > DATE: Thu Sep 19 08:31:18 2019 > UPTIME: 00:01:21 > LOAD AVERAGE: 0.16, 0.07, 0.02 > TASKS: 1343 > NODENAME: amd-ethanol > RELEASE: 5.3.0-rc7+ > VERSION: #4 SMP Thu Sep 19 08:14:00 EDT 2019 > MACHINE: x86_64 (2195 Mhz) > MEMORY: 127.9 GB > PANIC: "Kernel panic - not syncing: sysrq triggered crash" > PID: 9789 > COMMAND: "bash" > TASK: "ffff89711894ae80 [THREAD_INFO: ffff89711894ae80]" > CPU: 83 > STATE: TASK_RUNNING (PANIC) > > crash> kmem -s|grep -i invalid > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086ac099f0c5a4 > kmem: dma-kmalloc-512: slab:ffffd77680001c00 invalid freepointer:a6086ac099f0c5a4 > crash> I fail to see what that's trying to tell me? You have invalid pointers? > BTW: I also tried to fix the above problem in purgatory(), but there > are too many restricts in purgatory() context, for example: i can't > allocate new memory to create the identity mapping page table for SME > situation. This paragraph belongs under the "---" line below. > Currently, there are two places where the first 640k area is needed, > the first one is in the find_trampoline_placement(), another one is > in the reserve_real_mode(), and their content doesn't matter. > > To avoid the above error, when the crashkernel kernel command line > option is specified, lets reserve the remaining low 1MiB memory( > after reserving real mode memroy) so that the allocated memory does > not fall into the low 1MiB area, which makes us not to copy the first > 640k content to a backup region in purgatory(). This indicates that > it does not need to be included in crash dumps or used for anything > execept the processor trampolines that must live in the low 1MiB. > > In addition, also need to clean all the code related to the backup > region later. Ditto. > Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx> > --- > arch/x86/realmode/init.c | 11 +++++++++++ > 1 file changed, 11 insertions(+) > > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c > index 7dce39c8c034..1f0492830f2c 100644 > --- a/arch/x86/realmode/init.c > +++ b/arch/x86/realmode/init.c > @@ -34,6 +34,17 @@ void __init reserve_real_mode(void) > > memblock_reserve(mem, size); > set_real_mode_mem(mem); > + > +#ifdef CONFIG_KEXEC_CORE > + /* > + * When the crashkernel option is specified, only use the low > + * 1MiB for the real mode trampoline. > + */ > + if (strstr(boot_command_line, "crashkernel=")) { > + memblock_reserve(0, 1<<20); > + pr_info("Reserving the low 1MiB of memory for crashkernel\n"); > + } > +#endif /* CONFIG_KEXEC_CORE */ This ifdeffery needs to be a function in kernel/kexec_core.c which is called by reserve_real_mode(), instead. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
