linux-kernel - Re: [RFC v2 PATCH 04/13] KVM: Add fd-based memslot data structure and utils

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Date:   Tue, 23 Nov 2021 22:30:31 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org, Jonathan Corbet <corbet@....net>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com,
        david@...hat.com
Subject: Re: [RFC v2 PATCH 04/13] KVM: Add fd-based memslot data structure
 and utils

On Tue, Nov 23, 2021 at 09:41:34AM +0100, Paolo Bonzini wrote:
> On 11/19/21 14:47, Chao Peng wrote:
> > For fd-based memslot store the file references for shared fd and the
> > private fd (if any) in the memslot structure. Since there is no 'hva'
> > concept we cannot call hva_to_pfn() to get a pfn, instead kvm_memfd_ops
> > is added to get_pfn/put_pfn from the memory backing stores that provide
> > these fds.
> > 
> > Signed-off-by: Yu Zhang<yu.c.zhang@...ux.intel.com>
> > Signed-off-by: Chao Peng<chao.p.peng@...ux.intel.com>
> > ---
> 
> What about kvm_read/write_guest? 

Hmm, that would be another area KVM needs to change. Not totally
undoable.

> Maybe the proposal which kept
> userspace_addr for the shared fd is more doable (it would be great to
> ultimately remove the mandatory userspace mapping for the shared fd, but I
> think KVM is not quite ready for that).

Agree for short term keeping shared part unchanged would be making work
easy:) Let me try that to see if any blocker.

> 
> Paolo