Re: [PATCH] s390/kexec: Consolidate crash_map/unmap_reserved_pages() and arch_kexec_protect(unprotect)_crashkres()

[Xunlei Pang <xpang@redhat.com>]

Hi Bao,

On 2016/03/31 at 10:52, Baoquan He wrote:
> On 03/31/16 at 10:43am, Minfei Huang wrote:
>> On 03/30/16 at 08:30pm, Baoquan He wrote:
>>> Hi Xunlei,
>>>
>>> I have two questions.
>>>
>>> One is do we still need Minfei's patch if this patch is applied since
>>> you have completely delete crash_map/unmap_reserved_pages in
>>> kernel/kexec.c ?
>> I think it is necessary to apply my bug-fixing patch firstly before
>> apply this, since other maintainers can backport my bug-fixing patch to
>> fix issue for stable linux kernel.
> This is why previously I said you two need get together to discuss how
> to fix this issue and post. Two questions: 1st is Xunlei is doing a
> cleanup but leave the map/unmap there thought they are doing the same
> thing in different way; 2nd is your bug fix patch with his clean up. It
> looks totally mess, to reviewers and maintainers. So now I will leave
> these to other people interested to review because I personally don't
> like it, but I don't object it strongly since I don't like always aruging
> by type writing.
>

Thanks for your comments, and I'm fine with your concern.

There is a "historical" reason, we didn't expect these patches back then,
they were coming out gradually due to some discussion in the mailinglist.

It would be clear if these patches were reordered as follows:
Minfei's patchset:
[Patch01]   kexec: make a pair of map/unmap reserved pages in error path
[Patch02]   kexec: do a cleanup for function kexec_load

Then my patchset:
[Patch01]   kexec: introduce a protection mechanism for the crashkernel reserved memory
[Patch02]   s390/kexec: Consolidate crash_map/unmap_reserved_pages() and arch_kexec_protect(unprotect)_crashkres()
[Patch03(x86_64)]  kexec: provide arch_kexec_protect(unprotect)_crashkres()

I don't know if it is possible to reorder that since they are already in "linux-next", ask Andrew for help :-)

Regards,
Xunlei

>> Thanks
>> Minfei
>>
>>> On 03/30/16 at 07:47pm, Xunlei Pang wrote:
>>>> Commit 3f625002581b ("kexec: introduce a protection mechanism
>>>> for the crashkernel reserved memory") is a similar mechanism
>>>> for protecting the crash kernel reserved memory to previous
>>>> crash_map/unmap_reserved_pages() implementation, the new one
>>>> is more generic in name and cleaner in code (besides, some
>>>> arch may not be allowed to unmap the pgtable).
>>>>
>>>> Therefore, this patch consolidates them, and uses the new
>>>> arch_kexec_protect(unprotect)_crashkres() to replace former
>>>> crash_map/unmap_reserved_pages() which by now has been only
>>>> used by S390.
>>>>
>>>> The consolidation work needs the crash memory to be mapped
>>>> initially, so get rid of S390 crash kernel memblock removal
>>>> in reserve_crashkernel(). Once kdump kernel is loaded, the
>>>> new arch_kexec_protect_crashkres() implemented for S390 will
>>>> actually unmap the pgtable like before.
>>>>
>>>> The patch also fixed a S390 crash_shrink_memory() bad page warning
>>>> in passing due to not using memblock_reserve():
>>>>   BUG: Bad page state in process bash  pfn:7e400
>>>>   page:000003d101f90000 count:0 mapcount:1 mapping: (null) index:0x0
>>>>   flags: 0x0()
>>>>   page dumped because: nonzero mapcount
>>>>   Modules linked in: ghash_s390 prng aes_s390 des_s390 des_generic
>>>>   CPU: 0 PID: 1558 Comm: bash Not tainted 4.6.0-rc1-next-20160327 #1
>>>>        0000000073007a58 0000000073007ae8 0000000000000002 0000000000000000
>>>>        0000000073007b88 0000000073007b00 0000000073007b00 000000000022cf4e
>>>>        0000000000a579b8 00000000007b0dd6 0000000000791a8c
>>>>        000000000000000b
>>>>        0000000073007b48 0000000073007ae8 0000000000000000 0000000000000000
>>>>        070003d100000001 0000000000112f20 0000000073007ae8 0000000073007b48
>>>>   Call Trace:
>>>>   ([<0000000000112e0c>] show_trace+0x5c/0x78)
>>>>   ([<0000000000112ed4>] show_stack+0x6c/0xe8)
>>>>   ([<00000000003f28dc>] dump_stack+0x84/0xb8)
>>>>   ([<0000000000235454>] bad_page+0xec/0x158)
>>>>   ([<00000000002357a4>] free_pages_prepare+0x2e4/0x308)
>>>>   ([<00000000002383a2>] free_hot_cold_page+0x42/0x198)
>>>>   ([<00000000001c45e0>] crash_free_reserved_phys_range+0x60/0x88)
>>>>   ([<00000000001c49b0>] crash_shrink_memory+0xb8/0x1a0)
>>>>   ([<000000000015bcae>] kexec_crash_size_store+0x46/0x60)
>>>>   ([<000000000033d326>] kernfs_fop_write+0x136/0x180)
>>>>   ([<00000000002b253c>] __vfs_write+0x3c/0x100)
>>>>   ([<00000000002b35ce>] vfs_write+0x8e/0x190)
>>>>   ([<00000000002b4ca0>] SyS_write+0x60/0xd0)
>>>>   ([<000000000063067c>] system_call+0x244/0x264)
>>>>
>>>> Cc: Michael Holzheu <holzheu@linux.vnet.ibm.com>
>>>> Signed-off-by: Xunlei Pang <xlpang@redhat.com>
>>>> ---
>>>> Tested kexec/kdump on S390x
>>>>
>>>>  arch/s390/kernel/machine_kexec.c | 86 ++++++++++++++++++++++------------------
>>>>  arch/s390/kernel/setup.c         |  7 ++--
>>>>  include/linux/kexec.h            |  2 -
>>>>  kernel/kexec.c                   | 12 ------
>>>>  kernel/kexec_core.c              | 11 +----
>>>>  5 files changed, 54 insertions(+), 64 deletions(-)
>>>>
>>>> diff --git a/arch/s390/kernel/machine_kexec.c b/arch/s390/kernel/machine_kexec.c
>>>> index 2f1b721..1ec6cfc 100644
>>>> --- a/arch/s390/kernel/machine_kexec.c
>>>> +++ b/arch/s390/kernel/machine_kexec.c
>>>> @@ -35,6 +35,52 @@ extern const unsigned long long relocate_kernel_len;
>>>>  #ifdef CONFIG_CRASH_DUMP
>>>>  
>>>>  /*
>>>> + * Map or unmap crashkernel memory
>>>> + */
>>>> +static void crash_map_pages(int enable)
>>>> +{
>>>> +	unsigned long size = resource_size(&crashk_res);
>>>> +
>>>> +	BUG_ON(crashk_res.start % KEXEC_CRASH_MEM_ALIGN ||
>>>> +	       size % KEXEC_CRASH_MEM_ALIGN);
>>>> +	if (enable)
>>>> +		vmem_add_mapping(crashk_res.start, size);
>>>> +	else {
>>>> +		vmem_remove_mapping(crashk_res.start, size);
>>>> +		if (size)
>>>> +			os_info_crashkernel_add(crashk_res.start, size);
>>>> +		else
>>>> +			os_info_crashkernel_add(0, 0);
>>>> +	}
>>>> +}
>>>> +
>>>> +/*
>>>> + * Map crashkernel memory
>>>> + */
>>>> +static void crash_map_reserved_pages(void)
>>>> +{
>>>> +	crash_map_pages(1);
>>>> +}
>>>> +
>>>> +/*
>>>> + * Unmap crashkernel memory
>>>> + */
>>>> +static void crash_unmap_reserved_pages(void)
>>>> +{
>>>> +	crash_map_pages(0);
>>>> +}
>>>> +
>>>> +void arch_kexec_protect_crashkres(void)
>>> The second is in kernel I saw res is abbreviation of resource. So here
>>> what is the full name of crashkres?
>>>
>>>
>>>> +{
>>>> +	crash_unmap_reserved_pages();
>>>> +}
>>>> +
>>>> +void arch_kexec_unprotect_crashkres(void)
>>>> +{
>>>> +	crash_map_reserved_pages();
>>>> +}
>>>> +
>>>> +/*
>>>>   * PM notifier callback for kdump
>>>>   */
>>>>  static int machine_kdump_pm_cb(struct notifier_block *nb, unsigned long action,
>>>> @@ -43,12 +89,12 @@ static int machine_kdump_pm_cb(struct notifier_block *nb, unsigned long action,
>>>>  	switch (action) {
>>>>  	case PM_SUSPEND_PREPARE:
>>>>  	case PM_HIBERNATION_PREPARE:
>>>> -		if (crashk_res.start)
>>>> +		if (kexec_crash_image)
>>>>  			crash_map_reserved_pages();
>>>>  		break;
>>>>  	case PM_POST_SUSPEND:
>>>>  	case PM_POST_HIBERNATION:
>>>> -		if (crashk_res.start)
>>>> +		if (kexec_crash_image)
>>>>  			crash_unmap_reserved_pages();
>>>>  		break;
>>>>  	default:
>>>> @@ -147,42 +193,6 @@ static int kdump_csum_valid(struct kimage *image)
>>>>  }
>>>>  
>>>>  /*
>>>> - * Map or unmap crashkernel memory
>>>> - */
>>>> -static void crash_map_pages(int enable)
>>>> -{
>>>> -	unsigned long size = resource_size(&crashk_res);
>>>> -
>>>> -	BUG_ON(crashk_res.start % KEXEC_CRASH_MEM_ALIGN ||
>>>> -	       size % KEXEC_CRASH_MEM_ALIGN);
>>>> -	if (enable)
>>>> -		vmem_add_mapping(crashk_res.start, size);
>>>> -	else {
>>>> -		vmem_remove_mapping(crashk_res.start, size);
>>>> -		if (size)
>>>> -			os_info_crashkernel_add(crashk_res.start, size);
>>>> -		else
>>>> -			os_info_crashkernel_add(0, 0);
>>>> -	}
>>>> -}
>>>> -
>>>> -/*
>>>> - * Map crashkernel memory
>>>> - */
>>>> -void crash_map_reserved_pages(void)
>>>> -{
>>>> -	crash_map_pages(1);
>>>> -}
>>>> -
>>>> -/*
>>>> - * Unmap crashkernel memory
>>>> - */
>>>> -void crash_unmap_reserved_pages(void)
>>>> -{
>>>> -	crash_map_pages(0);
>>>> -}
>>>> -
>>>> -/*
>>>>   * Give back memory to hypervisor before new kdump is loaded
>>>>   */
>>>>  static int machine_kexec_prepare_kdump(void)
>>>> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
>>>> index d3f9688..5f00437 100644
>>>> --- a/arch/s390/kernel/setup.c
>>>> +++ b/arch/s390/kernel/setup.c
>>>> @@ -603,7 +603,7 @@ static void __init reserve_crashkernel(void)
>>>>  	crashk_res.start = crash_base;
>>>>  	crashk_res.end = crash_base + crash_size - 1;
>>>>  	insert_resource(&iomem_resource, &crashk_res);
>>>> -	memblock_remove(crash_base, crash_size);
>>>> +	memblock_reserve(crash_base, crash_size);
>>>>  	pr_info("Reserving %lluMB of memory at %lluMB "
>>>>  		"for crashkernel (System RAM: %luMB)\n",
>>>>  		crash_size >> 20, crash_base >> 20,
>>>> @@ -871,7 +871,6 @@ void __init setup_arch(char **cmdline_p)
>>>>  	setup_memory();
>>>>  
>>>>  	check_initrd();
>>>> -	reserve_crashkernel();
>>>>  #ifdef CONFIG_CRASH_DUMP
>>>>  	/*
>>>>  	 * Be aware that smp_save_dump_cpus() triggers a system reset.
>>>> @@ -890,7 +889,9 @@ void __init setup_arch(char **cmdline_p)
>>>>  	/*
>>>>  	 * Create kernel page tables and switch to virtual addressing.
>>>>  	 */
>>>> -        paging_init();
>>>> +	paging_init();
>>>> +
>>>> +	reserve_crashkernel();
>>>>  
>>>>          /* Setup default console */
>>>>  	conmode_default();
>>>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>>>> index f82d6a2..c76641c 100644
>>>> --- a/include/linux/kexec.h
>>>> +++ b/include/linux/kexec.h
>>>> @@ -230,8 +230,6 @@ extern void crash_kexec(struct pt_regs *);
>>>>  int kexec_should_crash(struct task_struct *);
>>>>  void crash_save_cpu(struct pt_regs *regs, int cpu);
>>>>  void crash_save_vmcoreinfo(void);
>>>> -void crash_map_reserved_pages(void);
>>>> -void crash_unmap_reserved_pages(void);
>>>>  void arch_crash_save_vmcoreinfo(void);
>>>>  __printf(1, 2)
>>>>  void vmcoreinfo_append_str(const char *fmt, ...);
>>>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>>>> index b73dc21..4384672 100644
>>>> --- a/kernel/kexec.c
>>>> +++ b/kernel/kexec.c
>>>> @@ -136,9 +136,6 @@ static int do_kexec_load(unsigned long entry, unsigned long nr_segments,
>>>>  	if (ret)
>>>>  		return ret;
>>>>  
>>>> -	if (flags & KEXEC_ON_CRASH)
>>>> -		crash_map_reserved_pages();
>>>> -
>>>>  	if (flags & KEXEC_PRESERVE_CONTEXT)
>>>>  		image->preserve_context = 1;
>>>>  
>>>> @@ -161,12 +158,6 @@ out:
>>>>  	if ((flags & KEXEC_ON_CRASH) && kexec_crash_image)
>>>>  		arch_kexec_protect_crashkres();
>>>>  
>>>> -	/*
>>>> -	 * Once the reserved memory is mapped, we should unmap this memory
>>>> -	 * before returning
>>>> -	 */
>>>> -	if (flags & KEXEC_ON_CRASH)
>>>> -		crash_unmap_reserved_pages();
>>>>  	kimage_free(image);
>>>>  	return ret;
>>>>  }
>>>> @@ -232,9 +223,6 @@ SYSCALL_DEFINE4(kexec_load, unsigned long, entry, unsigned long, nr_segments,
>>>>  
>>>>  	result = do_kexec_load(entry, nr_segments, segments, flags);
>>>>  
>>>> -	if ((flags & KEXEC_ON_CRASH) && kexec_crash_image)
>>>> -		arch_kexec_protect_crashkres();
>>>> -
>>>>  	mutex_unlock(&kexec_mutex);
>>>>  
>>>>  	return result;
>>>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>>>> index f826e11..58cd872 100644
>>>> --- a/kernel/kexec_core.c
>>>> +++ b/kernel/kexec_core.c
>>>> @@ -953,7 +953,6 @@ int crash_shrink_memory(unsigned long new_size)
>>>>  	start = roundup(start, KEXEC_CRASH_MEM_ALIGN);
>>>>  	end = roundup(start + new_size, KEXEC_CRASH_MEM_ALIGN);
>>>>  
>>>> -	crash_map_reserved_pages();
>>>>  	crash_free_reserved_phys_range(end, crashk_res.end);
>>>>  
>>>>  	if ((start == end) && (crashk_res.parent != NULL))
>>>> @@ -967,7 +966,6 @@ int crash_shrink_memory(unsigned long new_size)
>>>>  	crashk_res.end = end - 1;
>>>>  
>>>>  	insert_resource(&iomem_resource, ram_res);
>>>> -	crash_unmap_reserved_pages();
>>>>  
>>>>  unlock:
>>>>  	mutex_unlock(&kexec_mutex);
>>>> @@ -1549,17 +1547,12 @@ int kernel_kexec(void)
>>>>  }
>>>>  
>>>>  /*
>>>> - * Add and remove page tables for crashkernel memory
>>>> + * Protection mechanism for crashkernel reserved memory after
>>>> + * the kdump kernel is loaded.
>>>>   *
>>>>   * Provide an empty default implementation here -- architecture
>>>>   * code may override this
>>>>   */
>>>> -void __weak crash_map_reserved_pages(void)
>>>> -{}
>>>> -
>>>> -void __weak crash_unmap_reserved_pages(void)
>>>> -{}
>>>> -
>>>>  void __weak arch_kexec_protect_crashkres(void)
>>>>  {}
>>>>  
>>>> -- 
>>>> 1.8.3.1
>>>>
>>>>
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