linux-kernel - Re: [PATCH v1] KVM: x86: PMU Whitelist

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Message-ID: <CAOyeoRW5wx0F=9B24h29KkhUrbaORXVSoJufb4d-XzKiAsz+NQ@mail.gmail.com>
Date:   Tue, 4 Jun 2019 08:56:36 -0700
From:   Eric Hankland <ehankland@...gle.com>
To:     Wei Wang <wei.w.wang@...el.com>
Cc:     pbonzini@...hat.com, rkrcmar@...hat.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v1] KVM: x86: PMU Whitelist

On Mon, Jun 3, 2019 at 9:37 PM Wei Wang <wei.w.wang@...el.com> wrote:

> So, I'm not sure if "quantifying LLC contention" has been proved to
> be a real issue. If this is considered to be an issue:
>
> - without PMU, we could also write a piece of software to run in the
> guest to quantify that contention (e.g. by analyzing the memory access
> latency). How do you prevent this?
>
> - the same thing could also happen with the L1 cache (e.g. a vCPU
> and a host thread run 2 logical CPUs on the same core). If this is disabled
> as well, we may have very few events usable, and would like to see what you
> have on the whitelist.

Right - I'm aware there are other ways of detecting this - it's still
a class of events that some people don't want to surface. I'll ask if
there are any better examples.

Eric