[PATCH 1/2] kexec: Add quick kexec support for kernel
Sang Yan
sangyan at huawei.com
Fri Aug 14 04:21:56 EDT 2020
On 08/14/20 14:58, Dave Young wrote:
> On 08/14/20 at 01:52am, Sang Yan wrote:
>> In normal kexec, relocating kernel may cost 5 ~ 10 seconds, to
>> copy all segments from vmalloced memory to kernel boot memory,
>> because of disabled mmu.
>
> It is not the case on all archs, I assume your case is arm64, please
> describe it in patch log :)
>
Yes, it's particularly obvious on arm64. I will add it to the patch log,
and test how long it takes on x86 and other arch.
> About the arm64 problem, I know Pavel Tatashin is working on a patchset
> to improve the performance with enabling mmu.
>
> I added Pavel in cc, can you try his patches?
>
Thanks for your tips, I will try these patches. @Pavel.
Disable mmu after finishing copying pages?
>>
>> We introduce quick kexec to save time of copying memory as above,
>> just like kdump(kexec on crash), by using reserved memory
>> "Quick Kexec".
>
> This approach may have gain, but it also introduce extra requirements to
> pre-reserve a memory region. I wonder how Eric thinks about the idea.
>
> Anyway the "quick" name sounds not very good, I would suggest do not
> introduce a new param, and the code can check if pre-reserved region
> exist then use it, if not then fallback to old way.
>
aha. I agree with it, but I thought it may change the old behaviors of
kexec_load.
I will update a new patch without introducing new flags and new params.
Thanks a lot.
>>
>> Constructing quick kimage as the same as crash kernel,
>> then simply copy all segments of kimage to reserved memroy.
>>
>> We also add this support in syscall kexec_load using flags
>> of KEXEC_QUICK.
>>
>> Signed-off-by: Sang Yan <sangyan at huawei.com>
>> ---
>> arch/Kconfig | 10 ++++++++++
>> include/linux/ioport.h | 3 +++
>> include/linux/kexec.h | 13 +++++++++++-
>> include/uapi/linux/kexec.h | 3 +++
>> kernel/kexec.c | 10 ++++++++++
>> kernel/kexec_core.c | 41 +++++++++++++++++++++++++++++---------
>> 6 files changed, 70 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index 3329fa143637..eca782cb8e29 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -21,6 +21,16 @@ config KEXEC_CORE
>> config KEXEC_ELF
>> bool
>>
>> +config QUICK_KEXEC
>> + bool "Support for quick kexec"
>> + depends on KEXEC_CORE
>> + help
>> + Say y here to enable this feature.
>> + It use reserved memory to accelerate kexec, just like crash
>> + kexec, load new kernel and initrd to reserved memory, and
>> + boot new kernel on that memory. It will save the time of
>> + relocating kernel.
>> +
>> config HAVE_IMA_KEXEC
>> bool
>>
>> diff --git a/include/linux/ioport.h b/include/linux/ioport.h
>> index 6c2b06fe8beb..f37c632accbe 100644
>> --- a/include/linux/ioport.h
>> +++ b/include/linux/ioport.h
>> @@ -136,6 +136,9 @@ enum {
>> IORES_DESC_DEVICE_PRIVATE_MEMORY = 6,
>> IORES_DESC_RESERVED = 7,
>> IORES_DESC_SOFT_RESERVED = 8,
>> +#ifdef CONFIG_QUICK_KEXEC
>> + IORES_DESC_QUICK_KEXEC = 9,
>> +#endif
>> };
>>
>> /*
>> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
>> index 9e93bef52968..976bf9631070 100644
>> --- a/include/linux/kexec.h
>> +++ b/include/linux/kexec.h
>> @@ -269,9 +269,12 @@ struct kimage {
>> unsigned long control_page;
>>
>> /* Flags to indicate special processing */
>> - unsigned int type : 1;
>> + unsigned int type : 2;
>> #define KEXEC_TYPE_DEFAULT 0
>> #define KEXEC_TYPE_CRASH 1
>> +#ifdef CONFIG_QUICK_KEXEC
>> +#define KEXEC_TYPE_QUICK 2
>> +#endif
>> unsigned int preserve_context : 1;
>> /* If set, we are using file mode kexec syscall */
>> unsigned int file_mode:1;
>> @@ -331,6 +334,11 @@ extern int kexec_load_disabled;
>> #define KEXEC_FLAGS (KEXEC_ON_CRASH | KEXEC_PRESERVE_CONTEXT)
>> #endif
>>
>> +#ifdef CONFIG_QUICK_KEXEC
>> +#undef KEXEC_FLAGS
>> +#define KEXEC_FLAGS (KEXEC_ON_CRASH | KEXEC_QUICK)
>> +#endif
>> +
>> /* List of defined/legal kexec file flags */
>> #define KEXEC_FILE_FLAGS (KEXEC_FILE_UNLOAD | KEXEC_FILE_ON_CRASH | \
>> KEXEC_FILE_NO_INITRAMFS)
>> @@ -340,6 +348,9 @@ extern int kexec_load_disabled;
>> extern struct resource crashk_res;
>> extern struct resource crashk_low_res;
>> extern note_buf_t __percpu *crash_notes;
>> +#ifdef CONFIG_QUICK_KEXEC
>> +extern struct resource quick_kexec_res;
>> +#endif
>>
>> /* flag to track if kexec reboot is in progress */
>> extern bool kexec_in_progress;
>> diff --git a/include/uapi/linux/kexec.h b/include/uapi/linux/kexec.h
>> index 05669c87a0af..e3213614b713 100644
>> --- a/include/uapi/linux/kexec.h
>> +++ b/include/uapi/linux/kexec.h
>> @@ -12,6 +12,9 @@
>> /* kexec flags for different usage scenarios */
>> #define KEXEC_ON_CRASH 0x00000001
>> #define KEXEC_PRESERVE_CONTEXT 0x00000002
>> +#ifdef CONFIG_QUICK_KEXEC
>> +#define KEXEC_QUICK 0x00000004
>> +#endif
>> #define KEXEC_ARCH_MASK 0xffff0000
>>
>> /*
>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>> index f977786fe498..428af4cd3e1a 100644
>> --- a/kernel/kexec.c
>> +++ b/kernel/kexec.c
>> @@ -44,6 +44,9 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
>> int ret;
>> struct kimage *image;
>> bool kexec_on_panic = flags & KEXEC_ON_CRASH;
>> +#ifdef CONFIG_QUICK_KEXEC
>> + bool kexec_on_quick = flags & KEXEC_QUICK;
>> +#endif
>>
>> if (kexec_on_panic) {
>> /* Verify we have a valid entry point */
>> @@ -69,6 +72,13 @@ static int kimage_alloc_init(struct kimage **rimage, unsigned long entry,
>> image->type = KEXEC_TYPE_CRASH;
>> }
>>
>> +#ifdef CONFIG_QUICK_KEXEC
>> + if (kexec_on_quick) {
>> + image->control_page = quick_kexec_res.start;
>> + image->type = KEXEC_TYPE_QUICK;
>> + }
>> +#endif
>> +
>> ret = sanity_check_segment_list(image);
>> if (ret)
>> goto out_free_image;
>> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
>> index c19c0dad1ebe..b73dd749368b 100644
>> --- a/kernel/kexec_core.c
>> +++ b/kernel/kexec_core.c
>> @@ -70,6 +70,16 @@ struct resource crashk_low_res = {
>> .desc = IORES_DESC_CRASH_KERNEL
>> };
>>
>> +#ifdef CONFIG_QUICK_KEXEC
>> +struct resource quick_kexec_res = {
>> + .name = "Quick kexec",
>> + .start = 0,
>> + .end = 0,
>> + .flags = IORESOURCE_BUSY | IORESOURCE_SYSTEM_RAM,
>> + .desc = IORES_DESC_QUICK_KEXEC
>> +};
>> +#endif
>> +
>> int kexec_should_crash(struct task_struct *p)
>> {
>> /*
>> @@ -413,8 +423,10 @@ static struct page *kimage_alloc_normal_control_pages(struct kimage *image,
>> return pages;
>> }
>>
>> -static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>> - unsigned int order)
>> +
>> +static struct page *kimage_alloc_special_control_pages(struct kimage *image,
>> + unsigned int order,
>> + unsigned long end)
>> {
>> /* Control pages are special, they are the intermediaries
>> * that are needed while we copy the rest of the pages
>> @@ -444,7 +456,7 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>> size = (1 << order) << PAGE_SHIFT;
>> hole_start = (image->control_page + (size - 1)) & ~(size - 1);
>> hole_end = hole_start + size - 1;
>> - while (hole_end <= crashk_res.end) {
>> + while (hole_end <= end) {
>> unsigned long i;
>>
>> cond_resched();
>> @@ -479,7 +491,6 @@ static struct page *kimage_alloc_crash_control_pages(struct kimage *image,
>> return pages;
>> }
>>
>> -
>> struct page *kimage_alloc_control_pages(struct kimage *image,
>> unsigned int order)
>> {
>> @@ -490,8 +501,15 @@ struct page *kimage_alloc_control_pages(struct kimage *image,
>> pages = kimage_alloc_normal_control_pages(image, order);
>> break;
>> case KEXEC_TYPE_CRASH:
>> - pages = kimage_alloc_crash_control_pages(image, order);
>> + pages = kimage_alloc_special_control_pages(image, order,
>> + crashk_res.end);
>> + break;
>> +#ifdef CONFIG_QUICK_KEXEC
>> + case KEXEC_TYPE_QUICK:
>> + pages = kimage_alloc_special_control_pages(image, order,
>> + quick_kexec_res.end);
>> break;
>> +#endif
>> }
>>
>> return pages;
>> @@ -847,11 +865,11 @@ static int kimage_load_normal_segment(struct kimage *image,
>> return result;
>> }
>>
>> -static int kimage_load_crash_segment(struct kimage *image,
>> +static int kimage_load_special_segment(struct kimage *image,
>> struct kexec_segment *segment)
>> {
>> - /* For crash dumps kernels we simply copy the data from
>> - * user space to it's destination.
>> + /* For crash dumps kernels and quick kexec kernels
>> + * we simply copy the data from user space to it's destination.
>> * We do things a page at a time for the sake of kmap.
>> */
>> unsigned long maddr;
>> @@ -925,8 +943,13 @@ int kimage_load_segment(struct kimage *image,
>> result = kimage_load_normal_segment(image, segment);
>> break;
>> case KEXEC_TYPE_CRASH:
>> - result = kimage_load_crash_segment(image, segment);
>> + result = kimage_load_special_segment(image, segment);
>> + break;
>> +#ifdef CONFIG_QUICK_KEXEC
>> + case KEXEC_TYPE_QUICK:
>> + result = kimage_load_special_segment(image, segment);
>> break;
>> +#endif
>> }
>>
>> return result;
>> --
>> 2.19.1
>>
>>
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>> http://lists.infradead.org/mailman/listinfo/kexec
>>
>
> Thanks
> Dave
>
>
> .
>
Thanks
Sang Yan
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