On Mon, 2015-04-27 at 10:00 -0400, Linda Knippers wrote: > On 4/26/2015 2:16 PM, Alex Williamson wrote: > > On Sun, 2015-04-26 at 18:55 +0100, David Woodhouse wrote: > >> On Sun, 2015-04-26 at 11:33 -0600, Alex Williamson wrote: > >>> Curious why these weren't posted to the mailing list. > >> > >> Apologies for that. I was thinking of this tree as *only* collecting > >> the stuff for SVM, and had mostly forgotten the bug-fixes. I was going > >> to post the series once I had it all in better shape... and when it > >> became apparent that SVM wasn't going to make it for 4.1 I wasn't > >> actually going to push these early parts that *are* ready at all. But > >> then I started getting badgered about the X2APIC_OPT_OUT nonsense. > >> > >>> This one in particular not only ignores RMRR on IGD, but any PCI > >>> class display device. We may understand why IGD has RMRRs, but we > >>> certainly don't understand enough to ignore RMRRs for other GPUs, > >>> should they exist. > >> > >> If they exist, they'll exist for precisely the same reason — to let > >> the graphics device continue to render its framebuffer after the IOMMU > >> is turned on. > >> > >> For a discrete card with a discrete video BIOS, as opposed to chipset > >> -integrated stuff, I suspect it's actually much *less* likely that > >> there's any other weirdness going on. > > > > Hmm, we've seen RMRRs used for health monitoring and thermal control on > > other devices. These are exactly the kinds of RMRR use cases that > > causes us trouble via the IOMMU API. GPUs are potentially the smartest > > and most power hungry peripherals in a system. I don't see how thermal > > monitoring wouldn't be an attractive target for GPUs. Are you counting > > on system vendors not having sufficient pull with the GPU vendors to > > hack into their firmware? > > I can't speak for other vendors or for other use cases of RMRR but while > HP does use RMRRs for health and thermal monitoring for some devices, > we don't for GPUs. > > Older releases of firmware had RMRRs for GPUs only because we had them for > all slots. Firmware since about May 2013 no longer generates them for GPUs. > A platform running old firmware may see an RMRR for a GPU but the memory > region isn't being used. I assume that GPUs have other mechanisms for > reporting health and thermal information to the platform but don't really > know. > > I mention this because our use of RMRR has gotten attention in the past > so I understand Alex's concern and wanted to clarify our use as it relates > to GPUs. Other vendors may be doing other things so it may still be a > valid concern. This is only a comment on the use case, not on the patch. > > > I had sort of envisioned that we'd need to > > match the RMRRs to the use cases we know about for IGD to make sure > > nothing sneaks by. We should at least be documenting what the expected > > use cases are, the ranges involved, and why we can ignore them. > > I think that's a good idea.
David, Since this got pulled anyway, do you plan to follow-up with patches to limit the graphics RMRR exception to the known and acceptable uses and document them, or should I send a revert patch? I don't think what we have here is acceptable going forward or being backported to stable. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
