linux-kernel - Re: [PATCH v9 10/18] arm64: kexec: cpu_soft

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Date:   Wed, 29 Apr 2020 18:01:39 +0100
From:   James Morse <james.morse@....com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, ebiederm@...ssion.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        corbet@....net, catalin.marinas@....com, will@...nel.org,
        linux-arm-kernel@...ts.infradead.org, maz@...nel.org,
        vladimir.murzin@....com, matthias.bgg@...il.com,
        bhsharma@...hat.com, linux-mm@...ck.org, mark.rutland@....com,
        steve.capper@....com, rfontana@...hat.com, tglx@...utronix.de,
        selindag@...il.com
Subject: Re: [PATCH v9 10/18] arm64: kexec: cpu_soft_restart change argument
 types

Hi Pavel,

On 26/03/2020 03:24, Pavel Tatashin wrote:
> Change argument types from unsigned long to a more descriptive
> phys_addr_t.

For 'entry', which is a physical addresses, sure...

> diff --git a/arch/arm64/kernel/cpu-reset.h b/arch/arm64/kernel/cpu-reset.h
> index ed50e9587ad8..38cbd4068019 100644
> --- a/arch/arm64/kernel/cpu-reset.h
> +++ b/arch/arm64/kernel/cpu-reset.h
> @@ -10,17 +10,17 @@
>  
>  #include <asm/virt.h>
>  
> -void __cpu_soft_restart(unsigned long el2_switch, unsigned long entry,
> -	unsigned long arg0, unsigned long arg1, unsigned long arg2);

> +void __cpu_soft_restart(phys_addr_t el2_switch, phys_addr_t entry,
> +			phys_addr_t arg0, phys_addr_t arg1, phys_addr_t arg2);

This looks weird because its re-using the hyp-stub API, because it might call the hyp-stub
from the idmap. entry is passed in, so this isn't tied to kexec. Without tying it to
kexec, how do you know arg2 is a physical address?
I think it tried to be re-usable because 32bit has more users for this.

arg0-2 are unsigned long because the hyp-stub is just moving general purpose registers around.

This is to avoid casting?
Sure, its only got one caller. This thing evolved because the platform-has-EL2 and
kdump-while-KVM-was-running code was bolted on as they were discovered.


> -static inline void __noreturn cpu_soft_restart(unsigned long entry,
> -					       unsigned long arg0,
> -					       unsigned long arg1,
> -					       unsigned long arg2)
> +static inline void __noreturn cpu_soft_restart(phys_addr_t entry,
> +					       phys_addr_t arg0,
> +					       phys_addr_t arg1,
> +					       phys_addr_t arg2)
>  {
>  	typeof(__cpu_soft_restart) *restart;
>  
> -	unsigned long el2_switch = !is_kernel_in_hyp_mode() &&
> +	phys_addr_t el2_switch = !is_kernel_in_hyp_mode() &&
>  		is_hyp_mode_available();

What on earth happened here!?


>  	restart = (void *)__pa_symbol(__cpu_soft_restart);


Thanks,

James