Hi Linbo, thanks for your patch. On Wed, Oct 23, 2019 at 10:19:11PM +0800, 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> > --- > 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. > > 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. > > In addition, also need to clean all the code related to the backup > region later. > > arch/x86/realmode/init.c | 2 ++ > include/linux/kexec.h | 2 ++ > kernel/kexec_core.c | 13 +++++++++++++ > 3 files changed, 17 insertions(+) > > diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c > index 7dce39c8c034..064cc79a015d 100644 > --- a/arch/x86/realmode/init.c > +++ b/arch/x86/realmode/init.c > @@ -3,6 +3,7 @@ > #include <linux/slab.h> > #include <linux/memblock.h> > #include <linux/mem_encrypt.h> > +#include <linux/kexec.h> > > #include <asm/set_memory.h> > #include <asm/pgtable.h> > @@ -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) > diff --git a/include/linux/kexec.h b/include/linux/kexec.h > index 1776eb2e43a4..30acf1d738bc 100644 > --- a/include/linux/kexec.h > +++ b/include/linux/kexec.h > @@ -306,6 +306,7 @@ extern void __crash_kexec(struct pt_regs *); > extern void crash_kexec(struct pt_regs *); > int kexec_should_crash(struct task_struct *); > int kexec_crash_loaded(void); > +void __init kexec_reserve_low_1MiB(void); > void crash_save_cpu(struct pt_regs *regs, int cpu); > extern int kimage_crash_copy_vmcoreinfo(struct kimage *image); > > @@ -397,6 +398,7 @@ static inline void __crash_kexec(struct pt_regs *regs) { } > static inline void crash_kexec(struct pt_regs *regs) { } > static inline int kexec_should_crash(struct task_struct *p) { return 0; } > static inline int kexec_crash_loaded(void) { return 0; } > +static inline void __init kexec_reserve_low_1MiB(void) { } > #define kexec_in_progress false > #endif /* CONFIG_KEXEC_CORE */ > > diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c > index 15d70a90b50d..5bd89f1fee42 100644 > --- a/kernel/kexec_core.c > +++ b/kernel/kexec_core.c > @@ -37,6 +37,7 @@ > #include <linux/compiler.h> > #include <linux/hugetlb.h> > #include <linux/frame.h> > +#include <linux/memblock.h> > > #include <asm/page.h> > #include <asm/sections.h> > @@ -70,6 +71,18 @@ struct resource crashk_low_res = { > .desc = IORES_DESC_CRASH_KERNEL > }; > > +/* > + * When the crashkernel option is specified, only use the low > + * 1MiB for the real mode trampoline. > + */ > +void __init kexec_reserve_low_1MiB(void) > +{ > + if (strstr(boot_command_line, "crashkernel=")) { Could you comment on the issue of using strstr which was raised by Hatayama-san in response to an earlier revision of this patch? Thanks in advance! > + memblock_reserve(0, 1<<20); > + pr_info("Reserving the low 1MiB of memory for crashkernel\n"); > + } > +} > + > int kexec_should_crash(struct task_struct *p) > { > /* > -- > 2.17.1 > > > _______________________________________________ > kexec mailing list > kexec@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/kexec > _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
