Le lun. 1 févr. 2016 à 07:35, Jan Beulich <jbeul...@suse.com> a écrit :
> >>> On 01.02.16 at 13:28, <marma...@invisiblethingslab.com> wrote: > > On Mon, Feb 01, 2016 at 12:59:00AM -0700, Jan Beulich wrote: > >> >>> On 30.01.16 at 02:47, <marma...@invisiblethingslab.com> wrote: > >> > On Tue, Jan 26, 2016 at 04:37:05AM -0700, Jan Beulich wrote: > >> >> (re-adding xen-devel) > >> >> > >> >> >>> On 26.01.16 at 12:28, <thierry.laur...@gmail.com> wrote: > >> >> > Iommu=0 let the whole Qubes system work, without enforcing hardware > >> >> > compartimentalisation (iommu is enforced in software mode) > >> >> > > >> >> > When iommu=no-igfx is enforced, shell console boot up works > flawlessly. > > All > >> >> > domu machines get booted up. A system hang will happen at the > moment a > > domu > >> >> > machine does graphic rendering, > >> >> > >> >> And this is (other than I originally implied) without passing through > >> >> the IGD to the DomU? If so, I can't see the difference between a > >> >> guest rendering to its display (and vncviewer or whatever frontend > >> >> you use converting this to rendering on the host) and rendering > >> >> which originates in the host. > >> > > >> > Not sure if relevant, but window content is mapped from PV domU > directly > >> > into X server (in dom0) address space, using xc_map_foreign_pages. It > is > >> > done by hacking XShmAttach function. Not sure what graphics driver do > >> > with it next. Theoretically it could be possible that driver will > direct IGD > >> > to do DMA directly from that place, but I guess it does not. > >> > >> Interesting. This then really needs to be investigated from the > >> Qubes end rather than here. Possible resulting patches, if > >> relevant outside of that unusual setup, would then of course be > >> appreciated to be sent here. > > > Interesting fact: kde corrupts video buffer and make system hang faster then it's xfce counterparts. > > Note that Thierry said "The point is the iommu=no-igfx doesn't fix the > > issue", so either it is totally unrelated issue, or iommu=no-igfx is > > broken. Does iommu=no-igfx have any meaning when IDG is _not_ passed > > through to some domU? > > Yes: Iirc that option turns off the IOMMU responsible for IGD. > > I suppose passing iommu=dom0-passthrough to hypervisor and passing *intel_iommu*=*igfx_off to dom0 *may be what is desired here, but hypervisor refuses to boot without iommu=no-igfx flag. > And generally - is IOMMU used in any way for dom0 > > devices? > > Of course; by how much depends on what options you use (see > the command line doc). > Qubes does't use any specifics. > > > Is Linux kernel able to utilize it for its own purposes (my > > guess: no)? > > Under Xen? If so - indeed, no. > Wouldn't it be more natural if i915 iommu would be deactivated in kernel with *intel_iommu*=*igfx_off option being passed to dom0?* > > > Somehow unrelated: I've tried to get p2m iommu mapping using `xl > > debug-key o`, but it's too long (and xenconsoled isn't fast enough to > > catch it into hypervisor.log). Is is possible to enlarge console ring > > buffer at runtime? > > No. > > > If not, is `conring_size` the right option? > > Yes. > > > How large > > it should be (aprox) for `xl debug-key o` output? > > Depends on the amount of memory page tables need to be created > for as well as how fragmented memory was at the time memory > allocation for domains happens. I'm afraid you can only try it out. > > Jan > > Would it be possible to lend a x200 laptop to the most interested/motivated developer in making i915/iommu work correctly for this laptop? I don't see how I can troubleshoot this deeper by myself alone. Thierry
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