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  1. 12 Apr, 2016 32 commits
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  7. 29 Mar, 2016 3 commits
  9. 22 Mar, 2016 3 commits
    • Steven Rostedt (Red Hat)'s avatar
      tracing: Fix check for cpu online when event is disabled · 3a4377e4
      Steven Rostedt (Red Hat) authored 
      [ Upstream commit dc17147d ]

Commit f3775549 ("tracepoints: Do not trace when cpu is offline") added
a check to make sure that tracepoints only get called when the cpu is
online, as it uses rcu_read_lock_sched() for protection.

Commit 3a630178 ("tracing: generate RCU warnings even when tracepoints
are disabled") added lockdep checks (including rcu checks) for events that
are not enabled to catch possible RCU issues that would only be triggered if
a trace event was enabled. Commit f3775549 only stopped the warnings
when the trace event was enabled but did not prevent warnings if the trace
event was called when disabled.

To fix this, the cpu online check is moved to where the condition is added
to the trace event. This will place the cpu online check in all places that
it may be used now and in the future.

Cc: stable@vger.kernel.org # v3.18+
Fixes: f3775549 ("tracepoints: Do not trace when cpu is offline")
Fixes: 3a630178 ("tracing: generate RCU warnings even when tracepoints are disabled")
Reported-by: default avatarSudeep Holla <sudeep.holla@arm.com>
Tested-by: default avatarSudeep Holla <sudeep.holla@arm.com>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
      3a4377e4
    • Alex Deucher's avatar
      Revert "drm/radeon/pm: adjust display configuration after powerstate" · a077ab0b
      Alex Deucher authored 
      [ Upstream commit d74e766e ]

This reverts commit 39d42750.

This caused a regression on some older hardware.

bug:
https://bugzilla.kernel.org/show_bug.cgi?id=113891Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
      a077ab0b
    • Radim Krčmář's avatar
      KVM: VMX: disable PEBS before a guest entry · 306cc4da
      Radim Krčmář authored 
      [ Upstream commit 7099e2e1 ]

Linux guests on Haswell (and also SandyBridge and Broadwell, at least)
would crash if you decided to run a host command that uses PEBS, like
  perf record -e 'cpu/mem-stores/pp' -a

This happens because KVM is using VMX MSR switching to disable PEBS, but
SDM [2015-12] 18.4.4.4 Re-configuring PEBS Facilities explains why it
isn't safe:
  When software needs to reconfigure PEBS facilities, it should allow a
  quiescent period between stopping the prior event counting and setting
  up a new PEBS event. The quiescent period is to allow any latent
  residual PEBS records to complete its capture at their previously
  specified buffer address (provided by IA32_DS_AREA).

There might not be a quiescent period after the MSR switch, so a CPU
ends up using host's MSR_IA32_DS_AREA to access an area in guest's
memory.  (Or MSR switching is just buggy on some models.)

The guest can learn something about the host this way:
If the guest doesn't map address pointed by MSR_IA32_DS_AREA, it results
in #PF where we leak host's MSR_IA32_DS_AREA through CR2.

After that, a malicious guest can map and configure memory where
MSR_IA32_DS_AREA is pointing and can therefore get an output from
host's tracing.

This is not a critical leak as the host must initiate with PEBS tracing
and I have not been able to get a record from more than one instruction
before vmentry in vmx_vcpu_run() (that place has most registers already
overwritten with guest's).

We could disable PEBS just few instructions before vmentry, but
disabling it earlier shouldn't affect host tracing too much.
We also don't need to switch MSR_IA32_PEBS_ENABLE on VMENTRY, but that
optimization isn't worth its code, IMO.

(If you are implementing PEBS for guests, be sure to handle the case
 where both host and guest enable PEBS, because this patch doesn't.)

Fixes: 26a4f3c0 ("perf/x86: disable PEBS on a guest entry.")
Cc: <stable@vger.kernel.org>
Reported-by: default avatarJiří Olša <jolsa@redhat.com>
Signed-off-by: default avatarRadim Krčmář <rkrcmar@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarSasha Levin <sasha.levin@oracle.com>
      306cc4da
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