Re: [PATCH] arm64: PCI: Validate the node before setting node id for root bus

From: Baolin Wang <baolin.wang@linux.alibaba.com>
To: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: baolin.wang7@gmail.com, catalin.marinas@arm.com,
	Will Deacon <will@kernel.org>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: PCI: Validate the node before setting node id for root bus
Date: Sat, 3 Oct 2020 17:35:41 +0800	[thread overview]
Message-ID: <c9afea6a-4026-05ca-cb6b-9ab7cb513140@linux.alibaba.com> (raw)
In-Reply-To: <20201001085538.GA5142@e121166-lin.cambridge.arm.com>

> On Tue, Sep 29, 2020 at 11:41:29PM +0800, Baolin Wang wrote:
>> Hi,
>>
>> 锟斤拷 2020/9/28 23:23, Lorenzo Pieralisi 写锟斤拷:
>>> On Mon, Sep 28, 2020 at 10:49:57PM +0800, Baolin Wang wrote:
>>>> On Mon, Sep 28, 2020 at 03:00:55PM +0100, Will Deacon wrote:
>>>>> [+ Lorenzo]
>>>>>
>>>>> On Tue, Sep 22, 2020 at 06:33:24PM +0800, Baolin Wang wrote:
>>>>>> If the BIOS disabled the NUMA configuration, but did not change the
>>>>>> proximity domain description in the SRAT table, so the PCI root bus
>>>>>> device may get a incorrect node id by acpi_get_node().
>>>>>
>>>>> How "incorrect" are we talking here? What actually goes wrong? At some
>>>>> point, we have to trust what the firmware is telling us.
>>>>
>>>> What I mean is, if we disable the NUMA from BIOS
>>>
>>> Please define what this means ie are you removing SRAT from ACPI static
>>> tables ?
>>
>> Yes.
>>
>>>
>>>> but we did not change the PXM for the PCI devices,
>>>
>>> If a _PXM maps to a proximity domain that is not described in the SRAT
>>> your firmware is buggy.
>>
>> Sorry for confusing, that's not what I mean. When the BIOS disable the NUMA
>> (remove the SRAT table), but the PCI devices' _PXM description is still
>> available, which means we can still get the pxm from acpi_evaluate_integer()
>> in this case.
> 
> There should not be a _PXM object if the SRAT is not available, that's
> a firmware bug.
> 
>> So we can get below inconsistent log on ARM platform:
>> "No NUMA configuration found
>> PCI_bus 0000:00 on NUMA node 0
>> ...
>> PCI_bus 0000:e3 on NUMA node 1"
>>
>> On X86, the pci_acpi_root_get_node() will validate the node before setting
>> the node id for root bus. So I think we can add this validation for ARM
>> platform. Or anything else I missed?
> 
> We are not adding checks because x86 does it, it is certainly to paper
> over a firmware bug that you hopefully still have a chance to fix,
> let's do that instead of adding code that is not necessary.

Thanks for your input, and I will check this issue with our firmware 
colleagues again.

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