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

[Eric DeVolder]

On 2/22/22 21:58, Baoquan He wrote:
> 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.

I've moved these to arch/x86/kernel/crash.c within the #ifdef CONFIG_CRASH_HOTPLUG.
eric

> > Signed-off-by: Eric DeVolder <eric.devolder@xxxxxxxxxx>
> > ---
> >   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