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Date: Wed, 1 May 2024 21:10:53 +1000
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Subject: Re: [PATCH v9 12/19] arm64: acpi: Harden get_cpu_for_acpi_id()
 against missing CPU entry
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To: Jonathan Cameron <Jonathan.Cameron@huawei.com>,
 Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>,
 linux-pm@vger.kernel.org, loongarch@lists.linux.dev,
 linux-acpi@vger.kernel.org, linux-arch@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
 kvmarm@lists.linux.dev, x86@kernel.org, Russell King
 <linux@armlinux.org.uk>, "Rafael J . Wysocki" <rafael@kernel.org>,
 Miguel Luis <miguel.luis@oracle.com>, James Morse <james.morse@arm.com>,
 Salil Mehta <salil.mehta@huawei.com>,
 Jean-Philippe Brucker <jean-philippe@linaro.org>,
 Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>,
 Marc Zyngier <maz@kernel.org>, Hanjun Guo <guohanjun@huawei.com>
Cc: Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
 Dave Hansen <dave.hansen@linux.intel.com>, linuxarm@huawei.com,
 justin.he@arm.com, jianyong.wu@arm.com
References: <20240430142434.10471-1-Jonathan.Cameron@huawei.com>
 <20240430142434.10471-13-Jonathan.Cameron@huawei.com>
From: Gavin Shan <gshan@redhat.com>
In-Reply-To: <20240430142434.10471-13-Jonathan.Cameron@huawei.com>
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On 5/1/24 00:24, Jonathan Cameron wrote:
> In a review discussion of the changes to support vCPU hotplug where
> a check was added on the GICC being enabled if was was online, it was
                                                  ^^^^^^^

                                                  typo

> noted that there is need to map back to the cpu and use that to index
> into a cpumask. As such, a valid ID is needed.
> 
> If an MPIDR check fails in acpi_map_gic_cpu_interface() it is possible
> for the entry in cpu_madt_gicc[cpu] == NULL.  This function would
> then cause a NULL pointer dereference.   Whilst a path to trigger
> this has not been established, harden this caller against the
> possibility.
> 
> Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> ---
> v9: New patch in response to a question from Marc Zyngier.
>      Taking the easy way out - harden against a possible condition rather
>      than establishing it never happens!
> ---
>   arch/arm64/include/asm/acpi.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 

With the typo corrected:

Reviewed-by: Gavin Shan <gshan@redhat.com>

> diff --git a/arch/arm64/include/asm/acpi.h b/arch/arm64/include/asm/acpi.h
> index bc9a6656fc0c..a407f9cd549e 100644
> --- a/arch/arm64/include/asm/acpi.h
> +++ b/arch/arm64/include/asm/acpi.h
> @@ -124,7 +124,8 @@ static inline int get_cpu_for_acpi_id(u32 uid)
>   	int cpu;
>   
>   	for (cpu = 0; cpu < nr_cpu_ids; cpu++)
> -		if (uid == get_acpi_id_for_cpu(cpu))
> +		if (acpi_cpu_get_madt_gicc(cpu) &&
> +		    uid == get_acpi_id_for_cpu(cpu))
>   			return cpu;
>   
>   	return -EINVAL;