linux-kernel - Re: [PATCH v2 8/8] DO NOT MERGE: Hack-a-test to verify gpc invalidation+refresh

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Message-ID: <YmmmP0TSmj5CxV06@google.com>
Date:   Wed, 27 Apr 2022 20:23:27 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Mingwei Zhang <mizhang@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: Re: [PATCH v2 8/8] DO NOT MERGE: Hack-a-test to verify gpc
 invalidation+refresh

On Wed, Apr 27, 2022, David Woodhouse wrote:
> On Wed, 2022-04-27 at 01:40 +0000, Sean Christopherson wrote:
> > Add a VM-wide gfn=>pfn cache and a fake MSR to let userspace control the
> > cache.  On writes, reflect the value of the MSR into the backing page of
> > a gfn=>pfn cache so that userspace can detect if a value was written to
> > the wrong page, i.e. to a stale mapping.
> > 
> > Spin up 16 vCPUs (arbitrary) to use/refresh the cache, and another thread
> > to trigger mmu_notifier events and memslot updates.
> 
> Do you need the MSR hack? Can't you exercise this using Xen interrupt
> delivery or runstate information and the same kind of thread setup?

Yeah, I asumme it's possible, and medium/long term I definitely want to have a
proper test.  I went the hack route to get something that could hammer a cache
with minimal chance of a test bug.  I only have a rough idea of what the Xen stuff
does.