Re: [PATCH v4 05/10] crash hp: introduce helper functions un/map_crash_pages

Baoquan He
2022-02-23T03:58:36Z

On 02/09/22 at 02:57pm, Eric DeVolder wrote:
> This change introduces two new functions un/map_crash_pages()
> which are used to enable/disable access to the segments in the
> crash memory region. (Upon loading of a crash kernel, the
> crash memory regions are made inaccessible for integrity purposes.)
>
> For example, on x86_64, one of the segments is the elfcorehdr,
> which contains the list of CPUs and memories. This segment
> needs to be modified in response to hotplug events. These functions
> are used to obtain (and subsequenntly release) access to the crash
> memory region in order to make the modifications.
>
> QUESTION: These might need to be in arch/x86 as I'm not certain
> the implementatin is valid for all archs?

Since only x86_64 uses them, I would suggest putting them into x86_64,
near the caller.

>
> Signed-off-by: Eric DeVolder <eric.devolder@oracle.com>
> ---
> include/linux/kexec.h | 2 ++
> kernel/crash_core.c | 32 ++++++++++++++++++++++++++++++++
> 2 files changed, 34 insertions(+)
>
> diff --git a/include/linux/kexec.h b/include/linux/kexec.h
> index b11d75a6b2bc..e00c373c4095 100644
> --- a/include/linux/kexec.h
> +++ b/include/linux/kexec.h
> @@ -324,6 +324,8 @@ struct kimage {
> };
>
> #ifdef CONFIG_CRASH_HOTPLUG
> +void *map_crash_pages(unsigned long paddr, unsigned long size);
> +void unmap_crash_pages(void **ptr);
> void arch_crash_hotplug_handler(struct kimage *image,
> unsigned int hp_action, unsigned long a, unsigned long b);
> #define KEXEC_CRASH_HP_REMOVE_CPU 0
> diff --git a/kernel/crash_core.c b/kernel/crash_core.c
> index 256cf6db573c..0ff06d0698ad 100644
> --- a/kernel/crash_core.c
> +++ b/kernel/crash_core.c
> @@ -9,6 +9,7 @@
> #include <linux/init.h>
> #include <linux/utsname.h>
> #include <linux/vmalloc.h>
> +#include <linux/highmem.h>
>
> #include <asm/page.h>
> #include <asm/sections.h>
> @@ -491,3 +492,34 @@ static int __init crash_save_vmcoreinfo_init(void)
> }
>
> subsys_initcall(crash_save_vmcoreinfo_init);
> +
> +#ifdef CONFIG_CRASH_HOTPLUG
> +void *map_crash_pages(unsigned long paddr, unsigned long size)
> +{
> + /*
> + * NOTE: The addresses and sizes passed to this routine have
> + * already been fully aligned on page boundaries. There is no
> + * need for massaging the address or size.
> + */
> + void *ptr = NULL;
> +
> + /* NOTE: requires arch_kexec_[un]protect_crashkres() for write access */
> + if (size > 0) {
> + struct page *page = pfn_to_page(paddr >> PAGE_SHIFT);
> +
> + ptr = kmap(page);
> + }
> +
> + return ptr;
> +}
> +
> +void unmap_crash_pages(void **ptr)
> +{
> + if (ptr) {
> + if (*ptr)
> + kunmap(*ptr);
> + *ptr = NULL;
> + }
> +}
> +#endif
> +
> --
> 2.27.0
>