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Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with p
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event |
Date: |
Thu, 14 Mar 2013 16:50:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 |
Il 14/03/2013 15:23, Gleb Natapov ha scritto:
> On Thu, Mar 14, 2013 at 03:05:22PM +0100, Paolo Bonzini wrote:
>> Il 14/03/2013 14:56, Gleb Natapov ha scritto:
>>> On Thu, Mar 14, 2013 at 02:49:48PM +0100, Paolo Bonzini wrote:
>>>> Il 14/03/2013 13:34, Gleb Natapov ha scritto:
>>>>>> * it can be an ISA device; the interface is the I/O port and ACPI
>>>>>> support is provided just for convenience of the OSPM. In this case,
>>>>>> "-device pvevent" should just add handlers for the port. The ACPI
>>>>>> support is similar to what we do for other on-board ISA devices, for
>>>>>> example serial ports (the serial ports use PIIX PCI configuration
>>>>>> instead of fw-cfg, but that's a minor detail). It only needs to work
>>>>>> for port 0x505, so the fw-cfg data can be a single yes/no value and only
>>>>>> the _STA method needs patching. See piix4_pm_machine_ready in
>>>>>> hw/acpi_piix4.c.
>>>>>
>>>>> Again I think there is a big difference between well knows device and
>>>>> PV devices that we add at random location. And if we make the later
>>>>> configurable i.e it may or may not be present and location where it is
>>>>> present can be changed then we better not make a guest to do guesses.
>>>>
>>>> No guesses here on part of the guest, and no probing in the firmware
>>>> two. The same number is hard-coded in QEMU and the DSDT, which go in
>>>> pairs anyway, but _not_ in the guest kernel (also thanks to Hu's nice
>>>> trick with the methods).
>>>
>>> That's the problem. The number is not hard coded in QEMU only DSDT.
>>
>> It is hard-coded where the board creates it, or at least as the default
>> value of the qdev property.
>
> Default value that can be changes is not hard coded.
> Why do you allow change in one place, but not the other?
I'm just following the model of other ISA devices, I don't think there's
any difference in this respect between well-known and pv devices (also
because in the end all modern guests will use ACPI to discover even
well-known devices).
The board hardcodes 0x505 for pvpanic just like it hardcodes 0x3f8 for
serial ports.
>>> If you hard code it in QEMU (make it non configurable) and make device
>>> mandatory
>>> static DSDT make sense if provided by QEMU.
>>
>> You cannot make it mandatory due to versioned machine types, but my plan
>> would be to make it mandatory on "pc" and "pc-1.5". For that plan it
>> makes sense to have a static DSDT. Sorry if it was unclear.
>
> And then you will have to have different DSDT for pre pc-1.5. Dynamic
> patching solves exactly that problem.
Yes, but it's enough to patch _STA. Easier in both QEMU and the BIOS.
>>>> I think it's a nice compromise.
^^^ This still holds. :)
>>>>>> * ACPI support is a first-class part of the device. Each instance of
>>>>>> the device should be there in the ACPI tables. In this case the fw-cfg
>>>>>> data needs to be a list of ports, and it is probably simpler to combine
>>>>>> all the definitions in an SSDT that is dynamically-built (similar to
>>>>>> what we do for PCI hotplug slots). Or even provide a separate SSDT for
>>>>>> each instance of the device.
>>>>>>
>>>>>> I prefer the first, the second seems to be over-engineered.
>>>>>>
>>>>> Second is over-engineering indeed. The device should be singleton and
>>>>> fail if second instance is created. Do we have such capability in qdev?
>>>>
>>>> No, but why should it fail?
>>>>
>>> Why should it not? Guest cannot use more than on of them, why allow to
>>> create insane configs?
>>
>> Who cares? Insane ISA device configs anyway are not discoverable by
>> guests, you need to teach the guest about the device manually.
>>
> With proper ACPI they are discoverable. Since writing ACPI support for
> multiple pvpanic devices is clear case of over-engineering it is a
> courtesy to QEMU users to fail machine creation that cannot be properly
> described by ACPI.
We don't fail machine creation if someone wants to place a serial port
at 0x5678. With ISA it's basically garbage-in, garbage-out, I don't see
a reason to make pvpanic special in this respect.
Paolo
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, (continued)
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Markus Armbruster, 2013/03/20
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Gleb Natapov, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Paolo Bonzini, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Gleb Natapov, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Paolo Bonzini, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Gleb Natapov, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Gleb Natapov, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Paolo Bonzini, 2013/03/14
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Gleb Natapov, 2013/03/15
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Markus Armbruster, 2013/03/20
- Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Hu Tao, 2013/03/14
Re: [Qemu-devel] [PATCH v14 3/4] introduce pvevent device to deal with panicked event, Markus Armbruster, 2013/03/20
[Qemu-devel] [PATCH v14 4/4] pvevent: add document to describe the usage, Hu Tao, 2013/03/14