Re: [MINI-OS PATCH 02/12] kexec: add final kexec stage

[Jürgen Groß <jgross@xxxxxxxx>]

On 14.06.25 18:40, Jason Andryuk wrote:
> On Fri, Mar 21, 2025 at 5:25 AM Juergen Gross <jgross@xxxxxxxx> wrote:
> > Add the code and data definitions of the final kexec stage.
> >
> > Put the code and related data into a dedicated section in order to be
> > able to copy it to another location. For this reason there must be no
> > absolute relocations being used in the code or data.
> >
> > Being functionally related, add a function for adding a final kexec
> > action.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > --- /dev/null
> > +++ b/arch/x86/kexec.c
> > @@ -0,0 +1,109 @@
> > +
> > +/*
> > + * Final stage of kexec. Copies all data to the final destinations, zeroes
> > + * .bss and activates new kernel.
> > + * Must be called with interrupts off. Stack, code and data must be
> > + * accessible via identity mapped virtual addresses (virt == phys). Copying
> > + * and zeroing is done using virtual addresses.
> > + * No relocations inside the function are allowed, as it is copied to an
> > + * allocated page before being executed.
> "page" is stated here.  Do we need an ASSERT later?
Good idea. I'll ad an ASSERT() to the linker script in order to catch
such an issue at build time.

> > + */
> > +void do_kexec(void *kexec_page)
> > +{
> > +    unsigned long actions;
> > +    unsigned long stack;
> > +    unsigned long final;
> > +    unsigned long phys;
> > +
> > +    actions = get_kexec_addr(kexec_page, kexec_actions);
> > +    stack = get_kexec_addr(kexec_page, kexec_stack + KEXEC_STACK_LONGS);
> > +    final = get_kexec_addr(kexec_page, kexec_final);
> > +    phys = get_kexec_addr(kexec_page, kexec_phys);
> > +
> > +    memcpy(kexec_page, _kexec_start, KEXEC_SECSIZE);
> > +    asm("cli\n\t"
> > +        "mov %0, %%"ASM_SP"\n\t"
> > +        "mov %1, %%"ASM_ARG1"\n\t"
> > +        "mov %2, %%"ASM_ARG2"\n\t"
> > +        "jmp *%3"
> > +        :"=m" (stack), "=m" (actions), "=m" (phys)
> Aren't these inputs and not outputs?
Oh, of course they are.

> > +        :"m" (final));
> > +}
> > +
> > +#endif /* CONFIG_KEXEC */
>
> > diff --git a/include/kexec.h b/include/kexec.h
> > index 6fd96774..722be456 100644
> > --- a/include/kexec.h
> > +++ b/include/kexec.h
> > @@ -1,7 +1,34 @@
> > +
> > +int kexec_add_action(int action, void *dest, void *src, unsigned int len);
> > +
> > +#define KEXEC_SECSIZE ((unsigned long)_kexec_end - (unsigned long)_kexec_start)
> Add a build assertion here?  Or maybe the correct amount is allocated
> and it doesn't matter.
>
> Generally looks good.
Thanks,


Juergen

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