linux-kernel - Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE

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Date:   Mon, 11 Nov 2019 20:15:24 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Radim Krčmář <rkrcmar@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, KVM list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Adam Borowski <kilobyte@...band.pl>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being
 reserved

On 11/11/19 19:27, Sean Christopherson wrote:
>> Thanks for this clarification. I do want to put out though that
>> ZONE_DEVICE pages go idle, they don't get freed. As long as KVM drops
>> its usage on invalidate it's perfectly fine for KVM to operate on idle
>> ZONE_DEVICE pages. The common case is that ZONE_DEVICE pages are
>> accessed and mapped while idle. Only direct-I/O temporarily marks them
>> busy to synchronize with invalidate. KVM obviates that need by
>> coordinating with mmu-notifiers instead.
> Only the KVM MMU, e.g. page fault handler, coordinates via mmu_notifier,
> the kvm_vcpu_map() case would continue using pages across an invalidate.

Yes, and it gets/puts the page correctly.

Paolo