Re: [PATCH v4 1/3] kexec: Move vmcoreinfo out of the kernel's .bss section

[Xunlei Pang]

On 04/26/2017 at 03:19 PM, Dave Young wrote:
> Add ia64i list,  and s390 list although Michael has tested it
>
> On 04/20/17 at 07:39pm, Xunlei Pang wrote:
>> As Eric said,
>> "what we need to do is move the variable vmcoreinfo_note out
>> of the kernel's .bss section.  And modify the code to regenerate
>> and keep this information in something like the control page.
>>
>> Definitely something like this needs a page all to itself, and ideally
>> far away from any other kernel data structures.  I clearly was not
>> watching closely the data someone decided to keep this silly thing
>> in the kernel's .bss section."
>>
>> This patch allocates extra pages for these vmcoreinfo_XXX variables,
>> one advantage is that it enhances some safety of vmcoreinfo, because
>> vmcoreinfo now is kept far away from other kernel data structures.
>>
>> Suggested-by: Eric Biederman <ebiederm@xxxxxxxxxxxx>
>> Cc: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>
>> Cc: Juergen Gross <jgross@xxxxxxxx>
>> Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxx>
>> ---
>> v3->v4:
>> -Rebased on the latest linux-next
>> -Handle S390 vmcoreinfo_note properly
>> -Handle the newly-added xen/mmu_pv.c
>>
>>  arch/ia64/kernel/machine_kexec.c |  5 -----
>>  arch/s390/kernel/machine_kexec.c |  1 +
>>  arch/s390/kernel/setup.c         |  6 ------
>>  arch/x86/kernel/crash.c          |  2 +-
>>  arch/x86/xen/mmu_pv.c            |  4 ++--
>>  include/linux/crash_core.h       |  2 +-
>>  kernel/crash_core.c              | 27 +++++++++++++++++++++++----
>>  kernel/ksysfs.c                  |  2 +-
>>  8 files changed, 29 insertions(+), 20 deletions(-)
>>
>> diff --git a/arch/ia64/kernel/machine_kexec.c b/arch/ia64/kernel/machine_kexec.c
>> index 599507b..c14815d 100644
>> --- a/arch/ia64/kernel/machine_kexec.c
>> +++ b/arch/ia64/kernel/machine_kexec.c
>> @@ -163,8 +163,3 @@ void arch_crash_save_vmcoreinfo(void)
>>  #endif
>>  }
>>  
>> -phys_addr_t paddr_vmcoreinfo_note(void)
>> -{
>> -	return ia64_tpa((unsigned long)(char *)&vmcoreinfo_note);
>> -}
>> -
>> diff --git a/arch/s390/kernel/machine_kexec.c b/arch/s390/kernel/machine_kexec.c
>> index 49a6bd4..3d0b14a 100644
>> --- a/arch/s390/kernel/machine_kexec.c
>> +++ b/arch/s390/kernel/machine_kexec.c
>> @@ -246,6 +246,7 @@ void arch_crash_save_vmcoreinfo(void)
>>  	VMCOREINFO_SYMBOL(lowcore_ptr);
>>  	VMCOREINFO_SYMBOL(high_memory);
>>  	VMCOREINFO_LENGTH(lowcore_ptr, NR_CPUS);
>> +	mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
>>  }
>>  
>>  void machine_shutdown(void)
>> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
>> index 3ae756c..3d1d808 100644
>> --- a/arch/s390/kernel/setup.c
>> +++ b/arch/s390/kernel/setup.c
>> @@ -496,11 +496,6 @@ static void __init setup_memory_end(void)
>>  	pr_notice("The maximum memory size is %luMB\n", memory_end >> 20);
>>  }
>>  
>> -static void __init setup_vmcoreinfo(void)
>> -{
>> -	mem_assign_absolute(S390_lowcore.vmcore_info, paddr_vmcoreinfo_note());
>> -}
>> -
>>  #ifdef CONFIG_CRASH_DUMP
>>  
>>  /*
>> @@ -939,7 +934,6 @@ void __init setup_arch(char **cmdline_p)
>>  #endif
>>  
>>  	setup_resources();
>> -	setup_vmcoreinfo();
>>  	setup_lowcore();
>>  	smp_fill_possible_mask();
>>  	cpu_detect_mhz_feature();
>> diff --git a/arch/x86/kernel/crash.c b/arch/x86/kernel/crash.c
>> index 22217ec..44404e2 100644
>> --- a/arch/x86/kernel/crash.c
>> +++ b/arch/x86/kernel/crash.c
>> @@ -457,7 +457,7 @@ static int prepare_elf64_headers(struct crash_elf_data *ced,
>>  	bufp += sizeof(Elf64_Phdr);
>>  	phdr->p_type = PT_NOTE;
>>  	phdr->p_offset = phdr->p_paddr = paddr_vmcoreinfo_note();
>> -	phdr->p_filesz = phdr->p_memsz = sizeof(vmcoreinfo_note);
>> +	phdr->p_filesz = phdr->p_memsz = VMCOREINFO_NOTE_SIZE;
>>  	(ehdr->e_phnum)++;
>>  
>>  #ifdef CONFIG_X86_64
>> diff --git a/arch/x86/xen/mmu_pv.c b/arch/x86/xen/mmu_pv.c
>> index 9d9ae66..35543fa 100644
>> --- a/arch/x86/xen/mmu_pv.c
>> +++ b/arch/x86/xen/mmu_pv.c
>> @@ -2723,8 +2723,8 @@ void xen_destroy_contiguous_region(phys_addr_t pstart, unsigned int order)
>>  phys_addr_t paddr_vmcoreinfo_note(void)
>>  {
>>  	if (xen_pv_domain())
>> -		return virt_to_machine(&vmcoreinfo_note).maddr;
>> +		return virt_to_machine(vmcoreinfo_note).maddr;
>>  	else
>> -		return __pa_symbol(&vmcoreinfo_note);
>> +		return __pa(vmcoreinfo_note);
>>  }
>>  #endif /* CONFIG_KEXEC_CORE */
>> diff --git a/include/linux/crash_core.h b/include/linux/crash_core.h
>> index eb71a70..ba283a2 100644
>> --- a/include/linux/crash_core.h
>> +++ b/include/linux/crash_core.h
>> @@ -53,7 +53,7 @@
>>  #define VMCOREINFO_PHYS_BASE(value) \
>>  	vmcoreinfo_append_str("PHYS_BASE=%lx\n", (unsigned long)value)
>>  
>> -extern u32 vmcoreinfo_note[VMCOREINFO_NOTE_SIZE/4];
>> +extern u32 *vmcoreinfo_note;
>>  extern size_t vmcoreinfo_size;
>>  extern size_t vmcoreinfo_max_size;
>>  
>> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
>> index fcbd568..0321f04 100644
>> --- a/kernel/crash_core.c
>> +++ b/kernel/crash_core.c
>> @@ -14,10 +14,10 @@
>>  #include <asm/sections.h>
>>  
>>  /* vmcoreinfo stuff */
>> -static unsigned char vmcoreinfo_data[VMCOREINFO_BYTES];
>> -u32 vmcoreinfo_note[VMCOREINFO_NOTE_SIZE/4];
>> +static unsigned char *vmcoreinfo_data;
>>  size_t vmcoreinfo_size;
>> -size_t vmcoreinfo_max_size = sizeof(vmcoreinfo_data);
>> +size_t vmcoreinfo_max_size = VMCOREINFO_BYTES;
>> +u32 *vmcoreinfo_note;
>>  
>>  /*
>>   * parsing the "crashkernel" commandline
>> @@ -326,6 +326,9 @@ static void update_vmcoreinfo_note(void)
>>  
>>  void crash_save_vmcoreinfo(void)
>>  {
>> +	if (!vmcoreinfo_note)
>> +		return;
>> +
>>  	vmcoreinfo_append_str("CRASHTIME=%ld\n", get_seconds());
>>  	update_vmcoreinfo_note();
>>  }
>> @@ -356,11 +359,27 @@ void __weak arch_crash_save_vmcoreinfo(void)
>>  
>>  phys_addr_t __weak paddr_vmcoreinfo_note(void)
>>  {
>> -	return __pa_symbol((unsigned long)(char *)&vmcoreinfo_note);
>> +	return __pa(vmcoreinfo_note);
>>  }
>>  
>>  static int __init crash_save_vmcoreinfo_init(void)
>>  {
>> +	/* One page should be enough for VMCOREINFO_BYTES under all archs */
> Can we add a comment in the VMCOREINFO_BYTES header file about the one
> page assumption?
>
> Or just define the VMCOREINFO_BYTES as PAGE_SIZE instead of 4096

Yes, I considered this before, but VMCOREINFO_BYTES is also used by VMCOREINFO_NOTE_SIZE
definition which is exported to sysfs, also some platform has larger page size(64KB), so
I didn't touch this 4096 value.

I think I should use kmalloc() to allocate both of them, then move this comment to Patch3 
kimage_crash_copy_vmcoreinfo().

Regards,
Xunlei

>  
>> +	vmcoreinfo_data = (unsigned char *)get_zeroed_page(GFP_KERNEL);
>> +	if (!vmcoreinfo_data) {
>> +		pr_warn("Memory allocation for vmcoreinfo_data failed\n");
>> +		return -ENOMEM;
>> +	}
>> +
>> +	vmcoreinfo_note = alloc_pages_exact(VMCOREINFO_NOTE_SIZE,
>> +						GFP_KERNEL | __GFP_ZERO);
>> +	if (!vmcoreinfo_note) {
>> +		free_page((unsigned long)vmcoreinfo_data);
>> +		vmcoreinfo_data = NULL;
>> +		pr_warn("Memory allocation for vmcoreinfo_note failed\n");
>> +		return -ENOMEM;
>> +	}
>> +
>>  	VMCOREINFO_OSRELEASE(init_uts_ns.name.release);
>>  	VMCOREINFO_PAGESIZE(PAGE_SIZE);
>>  
>> diff --git a/kernel/ksysfs.c b/kernel/ksysfs.c
>> index 23cd706..c40a4e5 100644
>> --- a/kernel/ksysfs.c
>> +++ b/kernel/ksysfs.c
>> @@ -134,7 +134,7 @@ static ssize_t vmcoreinfo_show(struct kobject *kobj,
>>  {
>>  	phys_addr_t vmcore_base = paddr_vmcoreinfo_note();
>>  	return sprintf(buf, "%pa %x\n", &vmcore_base,
>> -		       (unsigned int)sizeof(vmcoreinfo_note));
>> +			(unsigned int)VMCOREINFO_NOTE_SIZE);
>>  }
>>  KERNEL_ATTR_RO(vmcoreinfo);
>>  
>> -- 
>> 1.8.3.1
>>
>>
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> Thanks
> Dave
>
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