On 20/07/15 14:55, Jan Beulich wrote: >>>> On 20.07.15 at 14:34, <andrew.coop...@citrix.com> wrote: >> On 20/07/15 13:24, Jan Beulich wrote: >>>>>> On 20.07.15 at 14:12, <andrew.coop...@citrix.com> wrote: >>>> On 17/07/15 20:05, Ting-Wei Lan wrote: >>>>> When using Linux >= 3.19 (commit 47591df) as dom0 on some Intel Ironlake >>>>> devices, It is possible to encounter graphics issues that make screen >>>>> unreadable or crash the system. It was reported in freedesktop bugzilla: >>>>> >>>>> https://bugs.freedesktop.org/show_bug.cgi?id=90037 >>>>> >>>>> As we still cannot find a proper fix for this problem, this patch adds >>>>> iommu=igfx_off option that is similar to Linux intel_iommu=igfx_off for >>>>> users to manually workaround the problem. >>>>> >>>>> Signed-off-by: Ting-Wei Lan <lant...@gmail.com> >>>> Having looked into this issue, the i915 driver has several workarounds >>>> in it for systems when the IOMMU is in use. In some cases there are >>>> plain errata, while in other cases there are specific hardware features >>>> which don't function if the IOMMU is enabled. >>>> >>>> In all cases this is gated on Linux's idea of whether the IOMMU is >>>> enabled. When used under Xen, Linux has no clue that the IOMMU exists, >>>> or that Xen has turned it on. >>> Perhaps it should just assume an IOMMU is in use when running under >>> Xen. Having inspected all those code places quite some time ago, I >>> came to the conclusion that making this assumption is better than >>> the current one of there not being an enabled IOMMU (and I adjusted >>> our kernels accordingly). >> In at least one case, an errata workaround involves issuing extra IOMMU >> commands. We cannot safely let even dom0 perform this. > Mind pointing out that one case? In our Xen kernels, IOMMU code > gets compiled out, so it is impossible for the driver to issue extra > IOMMU commands...
But a distro is going to want to ship a single kernel, especially with PVops these days. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
