Re: [XEN PATCH] tools/libs/light/libxl_pci.c: explicitly grant access to Intel IGD opregion

[Chuck Zmudzinski <brchuckz@xxxxxxxxxxxx>]

On 3/30/22 2:45 PM, Jason Andryuk wrote:
> On Fri, Mar 18, 2022 at 4:13 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
> > On 14.03.2022 04:41, Chuck Zmudzinski wrote:
> > > When gfx_passthru is enabled for the Intel IGD, hvmloader maps the IGD
> > > opregion to the guest but libxl does not grant the guest permission to
> > > access the mapped memory region. This results in a crash of the i915.ko
> > > kernel module in a Linux HVM guest when it needs to access the IGD
> > > opregion:
> > >
> > > Oct 23 11:36:33 domU kernel: Call Trace:
> > > Oct 23 11:36:33 domU kernel:  ? idr_alloc+0x39/0x70
> > > Oct 23 11:36:33 domU kernel:  drm_get_last_vbltimestamp+0xaa/0xc0 [drm]
> > > Oct 23 11:36:33 domU kernel:  drm_reset_vblank_timestamp+0x5b/0xd0 [drm]
> > > Oct 23 11:36:33 domU kernel:  drm_crtc_vblank_on+0x7b/0x130 [drm]
> > > Oct 23 11:36:33 domU kernel:  intel_modeset_setup_hw_state+0xbd4/0x1900 [i915]
> > > Oct 23 11:36:33 domU kernel:  ? _cond_resched+0x16/0x40
> > > Oct 23 11:36:33 domU kernel:  ? ww_mutex_lock+0x15/0x80
> > > Oct 23 11:36:33 domU kernel:  intel_modeset_init_nogem+0x867/0x1d30 [i915]
> > > Oct 23 11:36:33 domU kernel:  ? gen6_write32+0x4b/0x1c0 [i915]
> > > Oct 23 11:36:33 domU kernel:  ? intel_irq_postinstall+0xb9/0x670 [i915]
> > > Oct 23 11:36:33 domU kernel:  i915_driver_probe+0x5c2/0xc90 [i915]
> > > Oct 23 11:36:33 domU kernel:  ? vga_switcheroo_client_probe_defer+0x1f/0x40
> > > Oct 23 11:36:33 domU kernel:  ? i915_pci_probe+0x3f/0x150 [i915]
> > > Oct 23 11:36:33 domU kernel:  local_pci_probe+0x42/0x80
> > > Oct 23 11:36:33 domU kernel:  ? _cond_resched+0x16/0x40
> > > Oct 23 11:36:33 domU kernel:  pci_device_probe+0xfd/0x1b0
> > > Oct 23 11:36:33 domU kernel:  really_probe+0x222/0x480
> > > Oct 23 11:36:33 domU kernel:  driver_probe_device+0xe1/0x150
> > > Oct 23 11:36:33 domU kernel:  device_driver_attach+0xa1/0xb0
> > > Oct 23 11:36:33 domU kernel:  __driver_attach+0x8a/0x150
> > > Oct 23 11:36:33 domU kernel:  ? device_driver_attach+0xb0/0xb0
> > > Oct 23 11:36:33 domU kernel:  ? device_driver_attach+0xb0/0xb0
> > > Oct 23 11:36:33 domU kernel:  bus_for_each_dev+0x78/0xc0
> > > Oct 23 11:36:33 domU kernel:  bus_add_driver+0x12b/0x1e0
> > > Oct 23 11:36:33 domU kernel:  driver_register+0x8b/0xe0
> > > Oct 23 11:36:33 domU kernel:  ? 0xffffffffc06b8000
> > > Oct 23 11:36:33 domU kernel:  i915_init+0x5d/0x70 [i915]
> > > Oct 23 11:36:33 domU kernel:  do_one_initcall+0x44/0x1d0
> > > Oct 23 11:36:33 domU kernel:  ? do_init_module+0x23/0x260
> > > Oct 23 11:36:33 domU kernel:  ? kmem_cache_alloc_trace+0xf5/0x200
> > > Oct 23 11:36:33 domU kernel:  do_init_module+0x5c/0x260
> > > Oct 23 11:36:33 domU kernel:  __do_sys_finit_module+0xb1/0x110
> > > Oct 23 11:36:33 domU kernel:  do_syscall_64+0x33/0x80
> > > Oct 23 11:36:33 domU kernel:  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> > The call trace alone leaves open where exactly the crash occurred.
> > Looking at 5.17 I notice that the first thing the driver does
> > after mapping the range it to check the signature (both in
> > intel_opregion_setup()). As the signature can't possibly match
> > with no access granted to the underlying mappings, there shouldn't
> > be any further attempts to use the region in the driver; if there
> > are, I'd view this as a driver bug.
> Yes.  i915_driver_hw_probe does not check the return value of
> intel_opregion_setup(dev_priv) and just continues on.
>
> Chuck, the attached patch may help if you want to test it.
>
> Regards,
> Jason
I tested the patch - it made no noticeable difference. I still
get the same crash and call trace with the patch. Actually,
the call trace I posted here is only the first of three call
traces, and I still see all three call traces with the patch.
The patch is harmless and the i915 module with the patch
works normally when it can access the intel opregion.

Regards,

Chuck