On Thu, Jun 19, 2014 at 4:29 PM, Alex Williamson <alex.william...@redhat.com> wrote: > But is there a way for software to discover its location from the > device? If so, then I think we can recreate all the identity maps we'd > need for a guest from the device. If not, then we'd need to figure out > some IOMMU API extension to handle the mapping. The spec excerpt above > seems to indicate that hardware designers decided software doesn't need > to know about it, but the RMRR seems to be the "oh crap" moment when > they realized that yes we do need to know about it. Thanks,
It's all specified somewhere how it exactly works. But we've just had piles of fun trying to get the stolen range (i.e. for gfx buffer usage, no the gtt pte block) to work correctly and it's not been fun. The issue is that these registers are sw-defined and set by the bios. And the bios team occasionally smokes strong stuff and nilly-willy changes the definitions without telling anyone ... And we know that there's more reserved stuff in that stolen range that occasionally shouldn't be used by the driver. We have regular discussions with them. Otoh the same bios teams also set up the RMRR ranges with equallly predictable results. I don't have a recommendation here, but expect breakage no matter what you do. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
