On 10/29/19 at 10:10am, Lianbo Jiang wrote: > Kdump kernel will reuse the first 640k region because the real mode > trampoline has to work in this area. When the vmcore is dumped, the > old memory in this area may be accessed, therefore, kernel has to > copy the contents of the first 640k area to a backup region so that > kdump kernel can read the old memory from the backup area of the > first 640k area, which is done in the purgatory(). > > But, the current handling of copying the first 640k area runs into > problems when SME is enabled, kernel does not properly copy these > old memory to the backup area in the purgatory(), thereby, kdump > kernel reads out the encrypted contents, because the kdump kernel > must access the first kernel's memory with the encryption bit set > when SME is enabled in the first kernel. Please refer to this link: > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204793 > > Finally, it causes the following errors, and the crash tool gets > invalid pointers when parsing the 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> > > To avoid the above errors, when the crashkernel option is specified, > lets reserve the remaining low 1MiB memory(after reserving real mode > memory) 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 except the processor > trampolines that must live in the low 1MiB. > > Signed-off-by: Lianbo Jiang <lijiang@xxxxxxxxxx> > --- > arch/x86/include/asm/crash.h | 6 ++++++ > arch/x86/kernel/crash.c | 15 +++++++++++++++ > arch/x86/realmode/init.c | 2 ++ > 3 files changed, 23 insertions(+) > > diff --git a/arch/x86/include/asm/crash.h b/arch/x86/include/asm/crash.h > index 0acf5ee45a21..3e966a3dc823 100644 > --- a/arch/x86/include/asm/crash.h > +++ b/arch/x86/include/asm/crash.h > @@ -8,4 +8,10 @@ int crash_setup_memmap_entries(struct kimage *image, > struct boot_params *params); > void crash_smp_send_stop(void); > > +#ifdef CONFIG_KEXEC_CORE > +void __init kexec_reserve_low_1MiB(void); > +#else > +static inline void __init kexec_reserve_low_1MiB(void) { } > +#endif > + > #endif /* _ASM_X86_CRASH_H */ > diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c > index eb651fbde92a..144f519aef29 100644 > --- a/arch/x86/kernel/crash.c > +++ b/arch/x86/kernel/crash.c > @@ -24,6 +24,7 @@ > #include <linux/export.h> > #include <linux/slab.h> > #include <linux/vmalloc.h> > +#include <linux/memblock.h> > > #include <asm/processor.h> > #include <asm/hardirq.h> > @@ -39,6 +40,7 @@ > #include <asm/virtext.h> > #include <asm/intel_pt.h> > #include <asm/crash.h> > +#include <asm/cmdline.h> > > /* Used while preparing memory map entries for second kernel */ > struct crash_memmap_data { > @@ -68,6 +70,19 @@ static inline void cpu_crash_vmclear_loaded_vmcss(void) > rcu_read_unlock(); > } > > +/* > + * When the crashkernel option is specified, only use the low > + * 1MiB for the real mode trampoline. > + */ > +void __init kexec_reserve_low_1MiB(void) Thanks for the effort, Lianbo. I believe everyone is confident with this solution and fix. I have a tiny concern, why the function name is kexec_reserve_low_1MiB(), but not kexec_reserve_low_1M()? I searched in kernel code with below filter, didn't see MiB appearing in a function name. I am not sure about it either, just ask. git grep "_[1-9]*M " arch/ kernel/ mm include/ drivers/ net/ init fs crypto/ certs/ ipc lib Thanks Baoquan > +{ > + if (cmdline_find_option(boot_command_line, "crashkernel", > + NULL, 0) > 0) { > + memblock_reserve(0, 1<<20); > + pr_info("Reserving the low 1MiB of memory for crashkernel\n"); > + } > +} > + > #if defined(CONFIG_SMP) && defined(CONFIG_X86_LOCAL_APIC) > > static void kdump_nmi_callback(int cpu, struct pt_regs *regs) > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c > index 7dce39c8c034..b8bbd0017ca8 100644 > --- a/arch/x86/realmode/init.c > +++ b/arch/x86/realmode/init.c > @@ -8,6 +8,7 @@ > #include <asm/pgtable.h> > #include <asm/realmode.h> > #include <asm/tlbflush.h> > +#include <asm/crash.h> > > struct real_mode_header *real_mode_header; > u32 *trampoline_cr4_features; > @@ -34,6 +35,7 @@ void __init reserve_real_mode(void) > > memblock_reserve(mem, size); > set_real_mode_mem(mem); > + kexec_reserve_low_1MiB(); > } > > static void __init setup_real_mode(void) > -- > 2.17.1 > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
