linux-kernel - Re: [PATCH v2 04/27] drm/i915/gvt: Incorporate KVM memslot info into check for 2MiB GTT entry

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Message-ID: <ZBCrVkDjaFAIP5vc@google.com>
Date:   Tue, 14 Mar 2023 10:13:58 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yan Zhao <yan.y.zhao@...el.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhi Wang <zhi.a.wang@...el.com>, kvm@...r.kernel.org,
        intel-gvt-dev@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>
Subject: Re: [PATCH v2 04/27] drm/i915/gvt: Incorporate KVM memslot info into
 check for 2MiB GTT entry

On Tue, Mar 14, 2023, Yan Zhao wrote:
> On Fri, Mar 10, 2023 at 04:22:35PM -0800, Sean Christopherson wrote:
> > Honor KVM's max allowed page size when determining whether or not a 2MiB
> > GTT shadow page can be created for the guest.  Querying KVM's max allowed
> > size is somewhat odd as there's no strict requirement that KVM's memslots
> > and VFIO's mappings are configured with the same gfn=>hva mapping, but
> > the check will be accurate if userspace wants to have a functional guest,
> > and at the very least checking KVM's memslots guarantees that the entire
> > 2MiB range has been exposed to the guest.
> >
> hi Sean,
> I remember in our last discussion, the conclusion was that
> we can safely just use VFIO ABI (which is intel_gvt_dma_map_guest_page()
> introduced in patch 7) to check max mapping size. [1][2]

Gah, my apologies.  I completely forgot about dropping KVM's mapping size check.
I was pretty sure I was forgetting something, but couldn't figure out what I was
forgetting.  I'll drop this in the next version.

Thanks!