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

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Message-ID: <59007405.6070107@redhat.com>
Date:   Wed, 26 Apr 2017 18:18:45 +0800
From:   Xunlei Pang <xpang@...hat.com>
To:     Dave Young <dyoung@...hat.com>, Xunlei Pang <xlpang@...hat.com>
Cc:     Juergen Gross <jgross@...e.com>, linux-s390@...r.kernel.org,
        linux-ia64@...r.kernel.org, Baoquan He <bhe@...hat.com>,
        kexec@...ts.infradead.org, Petr Tesarik <ptesarik@...e.cz>,
        linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        akpm@...ux-foundation.org,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 1/3] kexec: Move vmcoreinfo out of the kernel's .bss
 section

On 04/26/2017 at 05:51 PM, Xunlei Pang wrote:
> 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@...ssion.com>
>>> Cc: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
>>> Cc: Juergen Gross <jgross@...e.com>
>>> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
>>> ---
>>> 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().

But on the other hand, using a separate page for them seems safer compared with
using frequently-used slab, what's your opinion?

Regards,
Xunlei

>
> 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
>>>
>>>
>>> _______________________________________________
>>> kexec mailing list
>>> kexec@...ts.infradead.org
>>> http://lists.infradead.org/mailman/listinfo/kexec
>> Thanks
>> Dave
>>
>> _______________________________________________
>> kexec mailing list
>> kexec@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec

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