RE: [PATCH linux-next v3 06/14] x86, crash: wrap crash dumping code into crash related ifdefs

[Michael Kelley]

From: Baoquan He <bhe@xxxxxxxxxx> Sent: Wednesday, January 24, 2024 8:10 PM
> 
> On 01/24/24 at 11:02pm, Michael Kelley wrote:
> > > diff --git a/arch/x86/kernel/cpu/mshyperv.c
> > > b/arch/x86/kernel/cpu/mshyperv.c
> > > index 01fa06dd06b6..f8163a59026b 100644
> > > --- a/arch/x86/kernel/cpu/mshyperv.c
> > > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > > @@ -210,6 +210,7 @@ static void hv_machine_shutdown(void)
> > >  		hyperv_cleanup();
> > >  }
> > >
> > > +#ifdef CONFIG_CRASH_DUMP
> > >  static void hv_machine_crash_shutdown(struct pt_regs *regs)
> > >  {
> > >  	if (hv_crash_handler)
> > > @@ -221,6 +222,7 @@ static void hv_machine_crash_shutdown(struct pt_regs *regs)
> > >  	/* Disable the hypercall page when there is only 1 active CPU. */
> > >  	hyperv_cleanup();
> > >  }
> > > +#endif
> > >  #endif /* CONFIG_KEXEC_CORE */
> >
> > Note that the #ifdef CONFIG_CRASH_DUMP is nested inside
> > #ifdef CONFIG_KEXEC_CODE here, and in the other Hyper-V code
> > just below.   It's also nested in xen_hvm_guest_init() at the bottom
> > of this patch.  But the KVM case of setting crash_shutdown is
> > not nested -- you changed #ifdef CONFIG_KEXEC_CORE to #ifdef
> > CONFIG_CRASH_DUMP.
> >
> > I think both approaches work because CONFIG_CRASH_DUMP implies
> > CONFIG_KEXEC_CORE, but I wonder if it would be better to *not* nest
> > in all cases.  I'd like to see the cases be consistent so in the future
> > someone doesn't wonder why there's a difference (unless there's
> > a reason for the difference that I missed).
> 
> I agree with you, it's a great suggestion. Thanks.
> 
> Do you think below draft patch includes all changes you are concerned
> about?

Yes, these changes look good as a delta to your original patch.

But also look at xen_hvm_guest_init().  It looks like your original patch
does nesting there as well, and it could probably be "un-nested".

Michael

> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c
> b/arch/x86/kernel/cpu/mshyperv.c
> index f8163a59026b..2e8cd5a4ae85 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -209,6 +209,7 @@ static void hv_machine_shutdown(void)
>  	if (kexec_in_progress)
>  		hyperv_cleanup();
>  }
> +#endif /* CONFIG_KEXEC_CORE */
> 
>  #ifdef CONFIG_CRASH_DUMP
>  static void hv_machine_crash_shutdown(struct pt_regs *regs)
> @@ -222,8 +223,7 @@ static void hv_machine_crash_shutdown(struct
> pt_regs *regs)
>  	/* Disable the hypercall page when there is only 1 active CPU. */
>  	hyperv_cleanup();
>  }
> -#endif
> -#endif /* CONFIG_KEXEC_CORE */
> +#endif /* CONFIG_CRASH_DUMP */
>  #endif /* CONFIG_HYPERV */
> 
>  static uint32_t  __init ms_hyperv_platform(void)
> @@ -497,9 +497,11 @@ static void __init ms_hyperv_init_platform(void)
>  	no_timer_check = 1;
>  #endif
> 
> -#if IS_ENABLED(CONFIG_HYPERV) && defined(CONFIG_KEXEC_CORE)
> +#if IS_ENABLED(CONFIG_HYPERV)
> +#if defined(CONFIG_KEXEC_CORE)
>  	machine_ops.shutdown = hv_machine_shutdown;
> -#ifdef CONFIG_CRASH_DUMP
> +#endif
> +#if defined(CONFIG_CRASH_DUMP)
>  	machine_ops.crash_shutdown = hv_machine_crash_shutdown;
>  #endif
>  #endif
> diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c
> index 1287b0d5962f..f3130f762784 100644
> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -826,7 +826,7 @@ void machine_halt(void)
>  	machine_ops.halt();
>  }
> 
> -#ifdef CONFIG_KEXEC_CORE
> +#ifdef CONFIG_CRASH_DUMP
>  void machine_crash_shutdown(struct pt_regs *regs)
>  {
>  	machine_ops.crash_shutdown(regs);