[Intel-gfx] [PATCH] drm/i915: Handle msr read failure gracefully
Chris Wilson
chris at chris-wilson.co.uk
Wed Jul 26 08:39:31 UTC 2017
Quoting Gabriel Krisman Bertazi (2017-07-26 06:30:16)
> Chris Wilson <chris at chris-wilson.co.uk> writes:
>
> > Quoting Gabriel Krisman Bertazi (2017-07-25 19:19:22)
> >> power = (power & 0x1f00) >> 8;
> >> units = 1000000 / (1 << power); /* convert to uJ */
> >> power = I915_READ(MCH_SECP_NRG_STTS);
> >
> > Just after this is a useless cast. Though it will be neater to kill the
> > (long long unsigned) and s/u64/unsigned long long/ so that we are
> > consistent with the rdmsrl_safe interface.
> >
> > Also we should use 1u << power as we allow power to be 31, or better yet
> > use:
> >
> > units = (power & 0x1f00) >> 8;
> > power = I915_READ(MCH_SECP_NRG_STTS);
> > power = (100000 * power) >> units; /* convert to uJ */
>
> Hi Chris,
>
> Thanks for your review. I have added your suggestions on a v2 of the
> patch below.
>
> >8
> Subject: [PATCH] drm/i915: Handle msr read failure gracefully
>
> 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>
-Chris
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