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From: Guenter Roeck <linux@roeck-us.net>
To: Igor Mammedov <imammedo@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>
Cc: "Jiahui Cen" <cenjiahui@huawei.com>,
	"Ard Biesheuvel" <ardb+tianocore@kernel.org>,
	qemu-devel@nongnu.org, "Bjorn Helgaas" <bhelgaas@google.com>,
	"Philippe Mathieu-Daudé" <philmd@redhat.com>,
	"Ard Biesheuvel" <ardb@kernel.org>
Subject: Re: aarch64 efi boot failures with qemu 6.0+
Date: Tue, 27 Jul 2021 04:32:11 -0700	[thread overview]
Message-ID: <a36dad2b-8e41-2275-bcb1-089318ea723e@roeck-us.net> (raw)
In-Reply-To: <20210727123603.6119c34c@redhat.com>

On 7/27/21 3:36 AM, Igor Mammedov wrote:
> On Tue, 27 Jul 2021 05:01:23 -0400
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
>> On Mon, Jul 26, 2021 at 10:12:38PM -0700, Guenter Roeck wrote:
>>> On 7/26/21 9:45 PM, Michael S. Tsirkin wrote:
>>>> On Mon, Jul 26, 2021 at 06:00:57PM +0200, Ard Biesheuvel wrote:
>>>>> (cc Bjorn)
>>>>>
>>>>> On Mon, 26 Jul 2021 at 11:08, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>>>>>>
>>>>>> On 7/26/21 12:56 AM, Guenter Roeck wrote:
>>>>>>> On 7/25/21 3:14 PM, Michael S. Tsirkin wrote:
>>>>>>>> On Sat, Jul 24, 2021 at 11:52:34AM -0700, Guenter Roeck wrote:
>>>>>>>>> Hi all,
>>>>>>>>>
>>>>>>>>> starting with qemu v6.0, some of my aarch64 efi boot tests no longer
>>>>>>>>> work. Analysis shows that PCI devices with IO ports do not instantiate
>>>>>>>>> in qemu v6.0 (or v6.1-rc0) when booting through efi. The problem affects
>>>>>>>>> (at least) ne2k_pci, tulip, dc390, and am53c974. The problem only
>>>>>>>>> affects
>>>>>>>>> aarch64, not x86/x86_64.
>>>>>>>>>
>>>>>>>>> I bisected the problem to commit 0cf8882fd0 ("acpi/gpex: Inform os to
>>>>>>>>> keep firmware resource map"). Since this commit, PCI device BAR
>>>>>>>>> allocation has changed. Taking tulip as example, the kernel reports
>>>>>>>>> the following PCI bar assignments when running qemu v5.2.
>>>>>>>>>
>>>>>>>>> [    3.921801] pci 0000:00:01.0: [1011:0019] type 00 class 0x020000
>>>>>>>>> [    3.922207] pci 0000:00:01.0: reg 0x10: [io  0x0000-0x007f]
>>>>>>>>> [    3.922505] pci 0000:00:01.0: reg 0x14: [mem 0x10000000-0x1000007f]
>>>>>
>>>>> IIUC, these lines are read back from the BARs
>>>>>    
>>>>>>>>> [    3.927111] pci 0000:00:01.0: BAR 0: assigned [io  0x1000-0x107f]
>>>>>>>>> [    3.927455] pci 0000:00:01.0: BAR 1: assigned [mem
>>>>>>>>> 0x10000000-0x1000007f]
>>>>>>>>>    
>>>>>
>>>>> ... and this is the assignment created by the kernel.
>>>>>    
>>>>>>>>> With qemu v6.0, the assignment is reported as follows.
>>>>>>>>>
>>>>>>>>> [    3.922887] pci 0000:00:01.0: [1011:0019] type 00 class 0x020000
>>>>>>>>> [    3.923278] pci 0000:00:01.0: reg 0x10: [io  0x0000-0x007f]
>>>>>>>>> [    3.923451] pci 0000:00:01.0: reg 0x14: [mem 0x10000000-0x1000007f]
>>>>>>>>>    
>>>>>
>>>>> The problem here is that Linux, for legacy reasons, does not support
>>>>> I/O ports <= 0x1000 on PCI, so the I/O assignment created by EFI is
>>>>> rejected.
>>>>>
>>>>> This might make sense on x86, where legacy I/O ports may exist, but on
>>>>> other architectures, this makes no sense.
>>>>
>>>>
>>>> Fixing Linux makes sense but OTOH EFI probably shouldn't create mappings
>>>> that trip up existing guests, right?
>>>>    
>>>
>>> I think it is difficult to draw a line. Sure, maybe EFI should not create
>>> such mappings, but then maybe qemu should not suddenly start to enforce
>>> those mappings for existing guests either.
>>
>> I would say both. But about QEMU actually I think you have a point here.
>> Re-reading the spec:
>>
>> 0: No (The operating system shall not ignore the PCI configuration that firmware has done
>> at boot time. However, the operating system is free to configure the devices in this hierarchy
>> that have not been configured by the firmware. There may be a reduced level of hot plug
>> capability support in this hierarchy due to resource constraints. This situation is the same as
>> the legacy situation where this _DSM is not provided.)
>> 1: Yes (The operating system may ignore the PCI configuration that the firmware has done
>> at boot time, and reconfigure/rebalance the resources in the hierarchy.)
>>
>>
>> I think I misread the spec previously, and understood it to mean that
>> 1 means must ignore. In fact 1 gives the most flexibility.
>> So why are we suddenly telling the guest it must not override
>> firmware?
>>
>> The commit log says
>>      The diffences could result in resource assignment failure.
>>
>> which is kind of vague ...
>>
>> Jiahui Cen, Igor, what do you think about it?
>> I'm inclined to revert 0cf8882fd06ba0aeb1e90fa6f23fce85504d7e14
>> at least for now.
> Looking at patch history, it seems consensus was that it's better to
> enforce firmware allocations.
> 
> Also letting OS do as it pleases might break PCI devices that
> don't tolerate reallocation. ex: firmware initializes PCI device
> IO/BARs and then fetches ACPI tables, which get patched with
> assigned resources.
> 

On the other side, _not_ letting the OS do as it pleases _will_ break
PCI devices with don't meet OS requirements.

That makes me curious: There has been a lot of "may", "might", and
"could" associated with commit 0cf8882fd06b. Does anyone happen to
have a specific example of a problem that was actually fixed with
this patch ?

Thanks,
Guenter

> to me returning 0 seems to be correct choice.
> In addition resource hinting also works via firmware allocations,
> if we revert the commit it might change those configs.
> 
> me wonders if there is a way make enforcement per device.
> 
>>> For my own testing, I simply reverted commit 0cf8882fd0 in my copy of
>>> qemu. That solves my immediate problem, giving us time to find a solution
>>> that is acceptable for everyone. After all, it doesn't look like anyone
>>> else has noticed the problem, so there is no real urgency.
>>>
>>> Thanks,
>>> Guenter
>>
>> Well it's not like we have an army of testers, I think we should
>> treat each problem report seriously ...
>>
> 



  reply	other threads:[~2021-07-27 11:33 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-24 18:52 Guenter Roeck
2021-07-25 22:14 ` Michael S. Tsirkin
2021-07-25 22:56   ` Guenter Roeck
2021-07-26  9:08     ` Philippe Mathieu-Daudé
2021-07-26 16:00       ` Ard Biesheuvel
2021-07-26 21:16         ` Bjorn Helgaas
2021-07-26 21:31           ` Bjorn Helgaas
2021-07-27  4:22             ` Guenter Roeck
2021-07-27 14:25               ` Bjorn Helgaas
2021-07-27  4:45         ` Michael S. Tsirkin
2021-07-27  5:12           ` Guenter Roeck
2021-07-27  7:04             ` Ard Biesheuvel
2021-07-27  9:02               ` Michael S. Tsirkin
2021-07-27  9:30               ` Michael S. Tsirkin
2021-07-27  9:50                 ` Ard Biesheuvel
2021-07-27 10:07                   ` Michael S. Tsirkin
2021-07-27 10:14                     ` Ard Biesheuvel
2021-07-27 11:18                 ` Guenter Roeck
2021-07-27  9:01             ` Michael S. Tsirkin
2021-07-27 10:36               ` Igor Mammedov
2021-07-27 11:32                 ` Guenter Roeck [this message]
2021-07-28 13:11                 ` Michael S. Tsirkin
2021-07-28 13:25                   ` Ard Biesheuvel
2021-07-28 14:03                     ` Guenter Roeck
2021-07-29  8:08                       ` Philippe Mathieu-Daudé
2021-07-29 14:42                         ` Bjorn Helgaas
2021-07-29 15:59                           ` Michael S. Tsirkin

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