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 1M memory(after reserving real mode memory) so that the allocated memory does not fall into the low 1M 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 1M. 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..3dff55f4ed9d 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 crash_reserve_low_1M(void); +#else +static inline void __init crash_reserve_low_1M(void) { } +#endif + #endif /* _ASM_X86_CRASH_H */ diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c index eb651fbde92a..db2301afade5 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 + * 1M for the real mode trampoline. + */ +void __init crash_reserve_low_1M(void) +{ + if (cmdline_find_option(boot_command_line, "crashkernel", + NULL, 0) > 0) { + memblock_reserve(0, 1<<20); + pr_info("Reserving the low 1M 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..262f83cad355 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); + crash_reserve_low_1M(); } static void __init setup_real_mode(void) -- 2.17.1 _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
