在 2019年10月29日 13:28, Baoquan He 写道: > 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()? Thanks for your comment, Baoquan. It means that kernel will reserve 1M 'Byte' memory, the function name does not have special meaning. Would you mind if i change it to the crash_reserve_low_1M()? void __init crash_reserve_low_1M(void) Thanks. Lianbo > 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
