linux-kernel - Re: [PATCH] vfio/type1: Unpin zero pages

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Message-ID: <Yw2heyQmvPgBe6f9@google.com>
Date:   Tue, 30 Aug 2022 05:34:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        david@...hat.com, lpivarc@...hat.com
Subject: Re: [PATCH] vfio/type1: Unpin zero pages

On Mon, Aug 29, 2022, Alex Williamson wrote:
> There's currently a reference count leak on the zero page.  We increment
> the reference via pin_user_pages_remote(), but the page is later handled
> as an invalid/reserved page, therefore it's not accounted against the
> user and not unpinned by our put_pfn().

Heh, kvm_pfn_to_refcounted_page() all over again.  is_zone_device_page() is the
other known case where a PageReserved page is refcounted.  But as KVM's comment
calls out, KVM's list was built through trial and error.