linux-kernel - Re: [PATCH v3 kvm/queue 04/16] KVM: Extend the memslot to support fd-based private memory

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Date:   Tue, 4 Jan 2022 17:34:51 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Chao Peng <chao.p.peng@...ux.intel.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        qemu-devel@...gnu.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        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: [PATCH v3 kvm/queue 04/16] KVM: Extend the memslot to support
 fd-based private memory

On Fri, Dec 31, 2021, Chao Peng wrote:
> On Thu, Dec 23, 2021 at 05:35:37PM +0000, Sean Christopherson wrote:
> > On Thu, Dec 23, 2021, Chao Peng wrote:
> > > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > > index 1daa45268de2..41434322fa23 100644
> > > --- a/include/uapi/linux/kvm.h
> > > +++ b/include/uapi/linux/kvm.h
> > > @@ -103,6 +103,17 @@ struct kvm_userspace_memory_region {
> > >  	__u64 userspace_addr; /* start of the userspace allocated memory */
> > >  };
> > >  
> > > +struct kvm_userspace_memory_region_ext {
> > > +	__u32 slot;
> > > +	__u32 flags;
> > > +	__u64 guest_phys_addr;
> > > +	__u64 memory_size; /* bytes */
> > > +	__u64 userspace_addr; /* hva */
> > 
> > Would it make sense to embed "struct kvm_userspace_memory_region"?
> > 
> > > +	__u64 ofs; /* offset into fd */
> > > +	__u32 fd;
> > 
> > Again, use descriptive names, then comments like "offset into fd" are unnecessary.
> > 
> > 	__u64 private_offset;
> > 	__u32 private_fd;
> 
> My original thought is the same fields might be used for shared memslot
> as well in future (e.g. there may be another KVM_MEM_* bit can reuse the
> same fields for shared slot) so non private-specific name may sound
> better. But definitely I have no objection and can use private_* names
> for next version unless there is other objection.

If that does happen, it's easy enough to wrap them in a union.