How to disable IDE DMA in KVM or in guest OS

How to disable IDE DMA in KVM or in guest OS

[Arthur Chunqi Li]

Hi Jan and there,

I want to disable IDE BMDMA in Qemu/KVM and let guest OS uses only PIO
mode. Are there any configurations in Qemu or KVM to disable the
hardware support of DMA?

I have tried to disable IDE DMA in guest OS booting params as follows:
ide-core.nodma=0.0 libata.dma=0 ide=nodma ide0=nodma

But I can also get the followings in dmesg:
[0.533276] ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc040 irq 14
[0.533641] ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc048 irq 15

and I do tracked irq 14 and irq 15 in ioapic_deliver when read/write disk.

How could I totally disable IDE BMDMA from guest's boot time?

Thanks,
Arthur

-- 
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China

Re: How to disable IDE DMA in KVM or in guest OS

[Jan Kiszka]

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On 2014-05-15 07:54, Arthur Chunqi Li wrote:
> Hi Jan and there,
> 
> I want to disable IDE BMDMA in Qemu/KVM and let guest OS uses only PIO
> mode. Are there any configurations in Qemu or KVM to disable the
> hardware support of DMA?

Not that I know. These features are built into the chipsets we emulate,
and there seems to be no option to disable them. Maybe the isapc will
not expose DMA capabilities - but will also lack a lot of other things
like PCI...

Jan

> 
> I have tried to disable IDE DMA in guest OS booting params as follows:
> ide-core.nodma=0.0 libata.dma=0 ide=nodma ide0=nodma
> 
> But I can also get the followings in dmesg:
> [0.533276] ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc040 irq 14
> [0.533641] ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc048 irq 15
> 
> and I do tracked irq 14 and irq 15 in ioapic_deliver when read/write disk.
> 
> How could I totally disable IDE BMDMA from guest's boot time?
> 
> Thanks,
> Arthur
> 



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Re: How to disable IDE DMA in KVM or in guest OS

[Arthur Chunqi Li]

On Thu, May 15, 2014 at 2:39 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
> On 2014-05-15 07:54, Arthur Chunqi Li wrote:
>> Hi Jan and there,
>>
>> I want to disable IDE BMDMA in Qemu/KVM and let guest OS uses only PIO
>> mode. Are there any configurations in Qemu or KVM to disable the
>> hardware support of DMA?
>
> Not that I know. These features are built into the chipsets we emulate,
> and there seems to be no option to disable them. Maybe the isapc will
> not expose DMA capabilities - but will also lack a lot of other things
> like PCI...

Well, if I boot guest Linux with ide-core.nodma=0.0 libata.dma=0
ide=nodma ide0=nodma, why are bmdma irqs (14 and 15) also triggered? I
think guest OS should only use PIO in this situation.

Arthur
>
> Jan
>
>>
>> I have tried to disable IDE DMA in guest OS booting params as follows:
>> ide-core.nodma=0.0 libata.dma=0 ide=nodma ide0=nodma
>>
>> But I can also get the followings in dmesg:
>> [0.533276] ata1: PATA max MWDMA2 cmd 0x1f0 ctl 0x3f6 bmdma 0xc040 irq 14
>> [0.533641] ata2: PATA max MWDMA2 cmd 0x170 ctl 0x376 bmdma 0xc048 irq 15
>>
>> and I do tracked irq 14 and irq 15 in ioapic_deliver when read/write disk.
>>
>> How could I totally disable IDE BMDMA from guest's boot time?
>>
>> Thanks,
>> Arthur
>>
>
>



-- 
Arthur Chunqi Li
Department of Computer Science
School of EECS
Peking University
Beijing, China

Re: How to disable IDE DMA in KVM or in guest OS

[Jan Kiszka]

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On 2014-05-15 08:55, Arthur Chunqi Li wrote:
> On Thu, May 15, 2014 at 2:39 PM, Jan Kiszka <jan.kiszka@web.de> wrote:
>> On 2014-05-15 07:54, Arthur Chunqi Li wrote:
>>> Hi Jan and there,
>>>
>>> I want to disable IDE BMDMA in Qemu/KVM and let guest OS uses only PIO
>>> mode. Are there any configurations in Qemu or KVM to disable the
>>> hardware support of DMA?
>>
>> Not that I know. These features are built into the chipsets we emulate,
>> and there seems to be no option to disable them. Maybe the isapc will
>> not expose DMA capabilities - but will also lack a lot of other things
>> like PCI...
> 
> Well, if I boot guest Linux with ide-core.nodma=0.0 libata.dma=0
> ide=nodma ide0=nodma, why are bmdma irqs (14 and 15) also triggered? I
> think guest OS should only use PIO in this situation.

To signal data availability e.g.? It's up to the guest driver if it
makes use of asynchronous notifications or polls for this.

Jan



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