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

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Date:   Tue, 04 Jun 2019 12:42:22 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Eric Hankland <ehankland@...gle.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 06/04/2019 01:30 AM, Eric Hankland wrote:
> On Sat, Jun 1, 2019 at 3:50 AM Wei Wang <wei.w.wang@...el.com> wrote:
>> My question is that have we proved that this indirect info leakage
>> indeed happens?
>> The spec states that the counter will count the related events generated by
>> the logical CPU with AnyThread=0. I would be inclined to trust the
>> hardware behavior
>> documented in the spec unless we could prove there is a problem.
> I'm not disputing the spec with regards to AnyThread=0; my point is
> that LLC contention can be quantified using the PMU regardless of
> whether or not you are measuring only the logical CPU you are running
> on.

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.


Best,
Wei