在 2019年10月24日 18:07, Simon Horman 写道: > 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? > Thank you, Simon and Hatayama-san. Lets talk about it here. > strstr() matches for example, ANYEXTRACHARACTERScrashkernel=ANYEXTRACHARACTERS. > > Is it enough to use cmdline_find_option_bool()? > The cmdline_find_option_bool() will find a boolean option, but the crashkernel option is not a boolean option, maybe it looks odd. So, should we use the cmdline_find_option() better? +#include <asm/cmdline.h> void __init kexec_reserve_low_1MiB(void) { - if (strstr(boot_command_line, "crashkernel=")) { + char buffer[4]; + + if (cmdline_find_option(boot_command_line, "crashkernel=", + buffer, sizeof(buffer))) { memblock_reserve(0, 1<<20); pr_info("Reserving the low 1MiB of memory for crashkernel\n"); } And here, no need to parse the arguments of crashkernel(sometimes, which has a complicated syntax), so the size of buffer should be enough. What's your opinion? Thanks Lianbo > 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
