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On x86, purgatory() copies the first 640K of memory to a backup region because the kernel needs those first 640K for the real mode trampoline during boot, among others. However, when SME is enabled, the kernel cannot properly copy the old memory to the backup area but reads only its encrypted contents. The result is that the crash tool gets invalid pointers when parsing vmcore: 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> So reserve the remaining low 1M memory when the crashkernel option is specified (after reserving real mode memory) so that allocated memory does not fall into the low 1M area and thus the copying of the contents of the first 640k to a backup region in purgatory() can be avoided altogether. This way, it does not need to be included in crash dumps or used for anything except the trampolines that must live in the low 1M. [ bp: Heavily rewrite commit message, flip check logic in crash_reserve_low_1M().] Signed-off-by: Lianbo Jiang <lijiang@redhat.com> Signed-off-by: Borislav Petkov <bp@suse.de> Cc: bhe@redhat.com Cc: Dave Young <dyoung@redhat.com> Cc: d.hatayama@fujitsu.com Cc: dhowells@redhat.com Cc: ebiederm@xmission.com Cc: horms@verge.net.au Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jürgen Gross <jgross@suse.com> Cc: kexec@lists.infradead.org Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Tom Lendacky <thomas.lendacky@amd.com> Cc: vgoyal@redhat.com Cc: x86-ml <x86@kernel.org> Link: https://lkml.kernel.org/r/20191108090027.11082-2-lijiang@redhat.com Link: https://bugzilla.kernel.org/show_bug.cgi?id=204793 |
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