On Sat, Mar 23, 2019 at 05:01:35PM -0400, Michael S. Tsirkin wrote: > On Thu, Mar 21, 2019 at 09:05:04PM -0300, Thiago Jung Bauermann wrote: > > Michael S. Tsirkin <mst@xxxxxxxxxx> writes: [snip] > > >> > Is there any justification to doing that beyond someone putting > > >> > out slow code in the past? > > >> > > >> The definition of the ACCESS_PLATFORM flag is generic and captures the > > >> notion of memory access restrictions for the device. Unfortunately, on > > >> powerpc pSeries guests it also implies that the IOMMU is turned on > > > > > > IIUC that's really because on pSeries IOMMU is *always* turned on. > > > Platform has no way to say what you want it to say > > > which is bypass the iommu for the specific device. > > > > Yes, that's correct. pSeries guests running on KVM are in a gray area > > where theoretically they use an IOMMU but in practice KVM ignores it. > > It's unfortunate but it's the reality on the ground today. :-/ Um.. I'm not sure what you mean by this. As far as I'm concerned there is always a guest-visible (paravirtualized) IOMMU, and that will be backed onto the host IOMMU when necessary. [Actually there is an IOMMU bypass hack that's used by the guest firmware, but I don't think we want to expose that] > Well it's not just the reality, virt setups need something that > emulated IOMMUs don't provide. That is not uncommon, e.g. > intel's VTD has a "cache mode" field which AFAIK is only used for virt. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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