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Message-ID: <56FF1F26.7020606@redhat.com>
Date: Sat, 2 Apr 2016 09:23:50 +0800
From: Xunlei Pang <xpang@...hat.com>
To: Michael Holzheu <holzheu@...ux.vnet.ibm.com>
Cc: Baoquan He <bhe@...hat.com>, Minfei Huang <mhuang@...hat.com>,
Heiko Carstens <heiko.carstens@...ibm.com>,
kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
ebiederm@...ssion.com, Martin Schwidefsky <schwidefsky@...ibm.com>,
akpm@...ux-foundation.org, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH] s390/kexec: Consolidate crash_map/unmap_reserved_pages()
and arch_kexec_protect(unprotect)_crashkres()
On 2016/04/02 at 01:41, Michael Holzheu wrote:
> Hello Xunlei again,
>
> Some initial comments below...
>
> On Wed, 30 Mar 2016 19:47:21 +0800
> Xunlei Pang <xlpang@...hat.com> 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);
>> + }
>> +}
> Please do not move these functions in the file. If you leave it at their
> old location, the patch will be *much* smaller.
In fact, I did this wanting avoiding adding extra declaration.
>> +
>> +/*
>> + * 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)
>> +{
>> + crash_unmap_reserved_pages();
>> +}
>> +
>> +void arch_kexec_unprotect_crashkres(void)
>> +{
>> + crash_map_reserved_pages();
>> +}
> Please replace the crash_(un)map_reserved_pages functions
> with the new arch_kexec_(un)protect() functions like the following:
>
> /*
> * Unmap crashkernel memory
> */
> void arch_kexec_protect_crashkres(void)
> {
> crash_map_pages(0);
> }
>
> /*
> * Map crashkernel memory
> */
> void arch_kexec_unprotect_crashkres(void)
> {
> crash_map_pages(1);
> }
>
> ... and remove the old functions.
Yea, this can also avoid the extra code moving above, will update next version.
>
>> +
>> +/*
>> * 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)
> Why this change?
arch_kexec_protect_crashkres() will do the unmapping once kdump kernel is loaded
(i.e. kexec_crash_image is non-NULL), so we should check "kexec_crash_image" here
and do the corresponding re-mapping.
NULL crashk_res_image means that kdump kernel is not loaded, in this case mapping is
already setup either initially in reserve_crashkernel() or by arch_kexec_unprotect_crashkres().
>
>> crash_map_reserved_pages();
> arch_kexec_unprotect_crashkres();
>
>> break;
>> case PM_POST_SUSPEND:
>> case PM_POST_HIBERNATION:
>> - if (crashk_res.start)
>> + if (kexec_crash_image)
> Why this change?
ditto
>
>> crash_unmap_reserved_pages();
> arch_kexec_protect_crashkres();
>
>> 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);
> I will discuss this next week in our team.
This can address the bad page warning when shrinking crashk_res.
>
>> 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();
> I will discuss this next week in our team.
Many Thanks!
Regards,
Xunlei
>
> Michael
>
>
> _______________________________________________
> kexec mailing list
> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
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