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Date:   Tue, 16 Aug 2022 10:16:51 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     David Matlack <dmatlack@google.com>
Cc:     Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Borislav Petkov <bp@suse.de>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        kvm@vger.kernel.org
Subject: Re: [PATCH 0/9] KVM: x86/mmu: Always enable the TDP MMU when TDP is
 enabled
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References: <20220815230110.2266741-1-dmatlack@google.com>
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On Mon, Aug 15, 2022 at 04:01:01PM -0700, David Matlack wrote:
> Patch 1 deletes the module parameter tdp_mmu and forces KVM to always
> use the TDP MMU when TDP hardware support is enabled.  The rest of the
> patches are related cleanups that follow (although the kvm_faultin_pfn()
> cleanups at the end are only tangentially related at best).
> 
> The TDP MMU was introduced in 5.10 and has been enabled by default since
> 5.15. At this point there are no known functionality gaps between the
> TDP MMU and the shadow MMU, and the TDP MMU uses less memory and scales
> better with the number of vCPUs. In other words, there is no good reason
> to disable the TDP MMU.

Then how are you going to test the shadow mmu code -- which I assume is
still relevant for the platforms that don't have this hardware support
you speak of?