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Message-ID: <5705005A.4000600@redhat.com>
Date:	Wed, 6 Apr 2016 20:26:02 +0800
From:	Xunlei Pang <xpang@...hat.com>
To:	Baoquan He <bhe@...hat.com>, Minfei Huang <mhuang@...hat.com>,
	akpm@...ux-foundation.org
Cc:	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
	ebiederm@...ssion.com,
	Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] s390/kexec: Consolidate crash_map/unmap_reserved_pages()
 and arch_kexec_protect(unprotect)_crashkres()

On 2016/03/31 at 11:52, Xunlei Pang wrote:
> 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 :-)

Ping Andrew :-)

>
> 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@...ux.vnet.ibm.com>
>>>>> Signed-off-by: Xunlei Pang <xlpang@...hat.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
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> kexec mailing list
>>>>> kexec@...ts.infradead.org
>>>>> http://lists.infradead.org/mailman/listinfo/kexec
>>>> _______________________________________________
>>>> kexec mailing list
>>>> kexec@...ts.infradead.org
>>>> http://lists.infradead.org/mailman/listinfo/kexec
>> _______________________________________________
>> kexec mailing list
>> kexec@...ts.infradead.org
>> http://lists.infradead.org/mailman/listinfo/kexec
>
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec

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