From: Nicholas Piggin <npiggin@gmail.com>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Michael Ellerman <mpe@ellerman.id.au>,
Paul Mackerras <paulus@ozlabs.org>,
linuxppc-dev@lists.ozlabs.org,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Anton Blanchard <anton@samba.org>,
sathnaga@linux.vnet.ibm.com
Subject: Re: [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths
Date: Mon, 19 Mar 2018 20:40:59 +1000 [thread overview]
Message-ID: <20180319204059.4c3a698e@roar.ozlabs.ibm.com> (raw)
In-Reply-To: <cdbe15845a5da965878b6344f69b6ed6dbabb87b.1521449527.git.naveen.n.rao@linux.vnet.ibm.com>
On Mon, 19 Mar 2018 14:43:00 +0530
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com> wrote:
> We have some C code that we call into from real mode where we cannot
> take any exceptions. Though the C functions themselves are mostly safe,
> if these functions are traced, there is a possibility that we may take
> an exception. For instance, in certain conditions, the ftrace code uses
> WARN(), which uses a 'trap' to do its job.
>
> For such scenarios, introduce a new field in paca 'ftrace_disabled',
> which is checked on ftrace entry before continuing. This field can then
> be set to a non-zero value to disable/pause ftrace, and reset to zero to
> resume ftrace.
>
> Since KVM is the only user for this currently, we guard the
> ftrace/mcount checks within CONFIG_KVM. This can later be removed
> if/when there are other users.
Why not test HSTATE_IN_GUEST then? Add ftrace_disabled if non-KVM users
come along.
Thanks,
Nick
next prev parent reply other threads:[~2018-03-19 10:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-19 9:12 [PATCH 0/2] Disable ftrace during kvm guest entry/exit Naveen N. Rao
2018-03-19 9:13 ` [PATCH 1/2] powerpc64/ftrace: Add a field in paca to disable ftrace in unsafe code paths Naveen N. Rao
2018-03-19 10:40 ` Nicholas Piggin [this message]
2018-03-19 18:53 ` Naveen N. Rao
2018-03-19 22:34 ` Michael Ellerman
2018-03-20 0:05 ` Nicholas Piggin
2018-03-20 11:02 ` Naveen N. Rao
2018-03-19 14:13 ` Steven Rostedt
2018-03-19 18:54 ` Naveen N. Rao
2018-03-19 9:13 ` [PATCH 2/2] powerpc64/ftrace: Disable ftrace during kvm guest entry/exit Naveen N. Rao
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