Re: [Qemu-devel] [PATCH 03/10] intel-iommu: add iommu lock

[Peter Xu]

On Sat, Apr 28, 2018 at 10:42:11AM +0800, Jason Wang wrote:

[...]

> Well, it's not about BQL specifically, it's about whether we have or need a
> generic thread safety solution for all IOMMUs.
> 
> We have more IOMMUs than just AMD, s390 and ppc:
> 
> # git grep imrc-\>translate\ =
> hw/alpha/typhoon.c:    imrc->translate = typhoon_translate_iommu;
> hw/dma/rc4030.c:    imrc->translate = rc4030_dma_translate;
> hw/i386/amd_iommu.c:    imrc->translate = amdvi_translate;
> hw/i386/intel_iommu.c:    imrc->translate = vtd_iommu_translate;
> hw/ppc/spapr_iommu.c:    imrc->translate = spapr_tce_translate_iommu;
> hw/s390x/s390-pci-bus.c:    imrc->translate = s390_translate_iommu;
> hw/sparc/sun4m_iommu.c:    imrc->translate = sun4m_translate_iommu;
> hw/sparc64/sun4u_iommu.c:    imrc->translate = sun4u_translate_iommu;

Sorry I didn't notice this one.  This point is valid.  But again, we
need to know whether they are thread-safe already.  For VT-d, it never
hurt to have this patch to fix its own problem, so above is not a
reason to not have current patch, since it solves different problems.
Basically I'll see the solution of above problem as a separate patch
as current one.

Meanwhile, even if we want to provide a general protection on that,
again I would prefer not using BQL but use some common and new
iommu-lock.  BQL can be a nightmare sometimes.

Thanks,

-- 
Peter Xu