linux-kernel - Re: [PATCH 1/1] arm64: kexec: machine_kexec should call __flush_icache

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Message-ID: <20180730161641.6zxxy3lxp27tznck@armageddon.cambridge.arm.com>
Date:   Mon, 30 Jul 2018 17:16:42 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Dave Kleikamp <dave.kleikamp@...cle.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] arm64: kexec: machine_kexec should call
 __flush_icache_range

On Mon, Jul 30, 2018 at 10:29:21AM -0500, Dave Kleikamp wrote:
> machine_kexec flushes the reboot_code_buffer from the icache
> after stopping the other cpus.
> 
> Commit 3b8c9f1cdfc5 ("arm64: IPI each CPU after invalidating the I-cache
> for kernel mappings") added an IPI call to flush_icache_range, which
> causes a hang here, so replace the call with __flush_icache_range

While machine_kexec() may be called with interrupts disabled (IIUC) and
we shouldn't IPI other CPUs, I don't understand why it hangs here. Are
there any other CPUs online at this point?

> Signed-off-by: Dave Kleikamp <dave.kleikamp@...cle.com>
> Cc: AKASHI Takahiro <takahiro.akashi@...aro.org>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  arch/arm64/kernel/machine_kexec.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index f62effc..e8c0283 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -184,7 +184,7 @@ void machine_kexec(struct kimage *kimage)
>  
>  	/* Flush the reboot_code_buffer in preparation for its execution. */
>  	__flush_dcache_area(reboot_code_buffer, arm64_relocate_new_kernel_size);
> -	flush_icache_range((uintptr_t)reboot_code_buffer,
> +	__flush_icache_range((uintptr_t)reboot_code_buffer,
>  		arm64_relocate_new_kernel_size);

That's probably needed, at least to avoid a WARN_ON(irqs_disabled()) via
smp_call_function_many().

-- 
Catalin