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

[Michael Holzheu]

Am Thu, 20 Apr 2017 19:39:32 +0800
schrieb Xunlei Pang <xlpang@xxxxxxxxxx>:

> 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>

Now s390 seems to work with the patches. I tested kdump and
zfcpdump.

Tested-by: Michael Holzheu <holzheu@xxxxxxxxxxxxxxxxxx>


> ---
> 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 */
> +	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);
>