[Intel-gfx] [PATCH] drm/i915: Handle msr read failure gracefully

[Chris Wilson]

Quoting Chris Wilson (2017-07-26 09:39:31)
> Quoting Gabriel Krisman Bertazi (2017-07-26 06:30:16)
> > When reading the i915_energy_uJ debugfs file, it tries to fetch
> > MSR_RAPL_POWER_UNIT, which might not be available, like in a vm
> > environment, causing the exception shown below.
> > 
> > We can easily prevent it by doing a rdmsrl_safe read instead, which will
> > handle the exception, allowing us to abort the debugfs file read.
> > 
> > This was caught by the new igt at debugfs_test@read_all_entries testcase in
> > the CI.
> > 
> >   unchecked MSR access error: RDMSR from 0x606 at rIP:0xffffffffa0078f66
> >     (i915_energy_uJ+0x36/0xb0 [i915])
> >   Call Trace:
> >    seq_read+0xdc/0x3a0
> >    full_proxy_read+0x4f/0x70
> >    __vfs_read+0x23/0x120
> >    ? putname+0x4f/0x60
> >    ? rcu_read_lock_sched_held+0x75/0x80
> >    ? entry_SYSCALL_64_fastpath+0x5/0xb1
> >    vfs_read+0xa0/0x150
> >    SyS_read+0x44/0xb0
> >    entry_SYSCALL_64_fastpath+0x1c/0xb1
> >   RIP: 0033:0x7f1f5e9f4500
> >   RSP: 002b:00007ffc77e65cf8 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
> >   RAX: ffffffffffffffda RBX: ffffffff8146e003 RCX: 00007f1f5e9f4500
> >   RDX: 0000000000000200 RSI: 00007ffc77e65d10 RDI: 0000000000000006
> >   RBP: ffffc900007abf88 R08: 0000000001eaff20 R09: 0000000000000000
> >   R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> >   R13: 0000000000000006 R14: 0000000000000005 R15: 0000000001eb94db
> >    ? __this_cpu_preempt_check+0x13/0x20
> > 
> > v2:
> >  - Drop unsigned long long cast and improve calculation (Chris)
> > 
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101901
> > Signed-off-by: Gabriel Krisman Bertazi <krisman at collabora.co.uk>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

And pushed, thanks for the fix.
-Chris