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Date: Wed, 15 Nov 2017 10:41:32 +0100
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 18/30] x86, kaiser: map virtually-addressed performance
 monitoring buffers
Message-ID: <20171115094132.ur4evzvsxvxdlivl@hirez.programming.kicks-ass.net>
References: <20171110193058.BECA7D88@viggo.jf.intel.com>
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 <20171114182009.jbhobwxlkfjb2t6i@hirez.programming.kicks-ass.net>
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 <alpine.LSU.2.11.1711141057510.2433@eggly.anvils>
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To: Hugh Dickins <hughd@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, moritz.lipp@iaik.tugraz.at, daniel.gruss@iaik.tugraz.at, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, luto@kernel.org, torvalds@linux-foundation.org, keescook@google.com, x86@kernel.org

On Tue, Nov 14, 2017 at 11:10:23AM -0800, Hugh Dickins wrote:
> I was about to agree, but now I'm not so sure.  I don't know much
> about these PMC things, but at a glance it looks like what is reserved
> by x86_reserve_hardware() may later be released by x86_release_hardware(),
> and then later reserved again by x86_reserve_hardware().  And although
> the static per-cpu area would be zeroed the first time, the second time
> it will contain data left over from before, so really needs the memset?

Ah, yes. It does get reused. I think its still fine, but yes lets keep
it. Better safe than sorry and its not a hot path in any case.

Thanks!

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