Re: [PATCH 1/2] kexec: Add quick kexec support for kernel

From: Dave Young
Date: Fri Aug 14 2020 - 02:59:05 EST

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In reply to: Sang Yan: "[PATCH 2/2] arm64: Reserve memory for quick kexec"
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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 :)

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?

>
> 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.

>
> 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@xxxxxxxxxx>
> ---
> 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
>
>
> _______________________________________________
> kexec mailing list
> kexec@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/kexec
>

Thanks
Dave

Next message: Michal Hocko: "Re: [PATCH] mm: include CMA pages in lowmem_reserve at boot"
Previous message: Thomas Bogendoerfer: "Re: [PATCH] MIPS: Loongson: Set CONFIG_FRAME_WARN=2048 in loongson3_defconfig to fix build warning"
In reply to: Sang Yan: "[PATCH 2/2] arm64: Reserve memory for quick kexec"
Next in thread: Sang Yan: "Re: [PATCH 1/2] kexec: Add quick kexec support for kernel"
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