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Re: [Xen-devel] dom0 as pvh boot problem

On Wed, Jan 7, 2015 at 2:51 AM, Jan Beulich <JBeulich@xxxxxxxx> wrote:
>>>> On 06.01.15 at 23:20, <ufimtseva@xxxxxxxxx> wrote:
>> On Mon, Jan 5, 2015 at 3:44 AM, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>> >>> Elena Ufimtseva <ufimtseva@xxxxxxxxx> 01/02/15 7:32 PM >>>
>>> >The last successful command is the reading status register of second IOMMU
>>> >unit:
>>> >
>>> ><snip from iommu_enable_translation() in
>>> >./xen/drivers/passthrough/vtd/iommu.c>
>>> >
>>> >746:    sts = dmar_readl(iommu->reg, DMAR_GSTS_REG);
>>> >747:    dmar_writel(iommu->reg, DMAR_GCMD_REG, sts | DMA_GCMD_TE);
>>> >
>>> ></snip>
>>> >
>>> >After dmar_writel for second iommu the machine hangs.
>>> That's rather odd - you say it doesn't even reach the IOMMU_WAIT_OP()
>>> right after that?
>> Thats odd, last tests I did show that it does complete the write to the
>> control register
>> of the second drhd, but I cannot say if it reaches IOMMU_WAIT_OP() as right
>> after this write it hangs.
>> I tried to enable iommu's in reverse order with the same result.
> "The same" being it hanging on the second one being enabled, or
> no hanging on the one getting enabled first?

"The same" meant the same behaviour.

Does not matter if iommu#1 (numbered in the order of enumeration)
enabled first or after iommu#0,
machine hangs after enabling translation by writing to comman reg. of iommu#1.

>>> That would suggest a fault or other abnormal condition
>>> raised by the translation enabling (i.e. some problem with the page tables,
>>> albeit that should then have been a problem for the first IOMMU already).
>> I wonder if such problem can be diagnosed without interrupt. Maybe
>> reflected in error logging event registers?
> Sure - you'd need to poll those registers, which you can't if the
> CPU really hangs. Or maybe you could try to monitor the IOMMU
> state from another CPU...

Thanks Jan for advise.
Yes, I can do this, pin dom0 to one cpu and poll the registers from another.

> Jan


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