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

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Date:   Fri, 31 Dec 2021 10:53:44 +0800
From:   Chao Peng <chao.p.peng@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.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 Thu, Dec 23, 2021 at 05:35:37PM +0000, Sean Christopherson wrote:
> On Thu, Dec 23, 2021, Chao Peng wrote:
> 
> > +	struct file *file;
> 
> Please use more descriptive names, shaving characters is not at all priority.
> 
> > +	u64 ofs;
> 
> I believe this should be loff_t.
> 
> 	struct file *private_file;
> 	struct loff_t private_offset;
> 
> >  };
> >  
> > +static inline bool kvm_slot_is_private(const struct kvm_memory_slot *slot)
> > +{
> > +	if (slot && (slot->flags & KVM_MEM_PRIVATE))
> > +		return true;
> > +	return false;
> 
> 	return slot && (slot->flags & KVM_MEM_PRIVATE);
> 
> > +}
> > +
> >  static inline bool kvm_slot_dirty_track_enabled(const struct kvm_memory_slot *slot)
> >  {
> >  	return slot->flags & KVM_MEM_LOG_DIRTY_PAGES;
> > 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.

Thanks,
Chao
> 
> > +	__u32 padding[5];
> > +};
> > +
> >  /*
> >   * The bit 0 ~ bit 15 of kvm_memory_region::flags are visible for userspace,
> >   * other bits are reserved for kvm internal use which are defined in
> > @@ -110,6 +121,7 @@ struct kvm_userspace_memory_region {
> >   */
> >  #define KVM_MEM_LOG_DIRTY_PAGES	(1UL << 0)
> >  #define KVM_MEM_READONLY	(1UL << 1)
> > +#define KVM_MEM_PRIVATE		(1UL << 2)
> >  
> >  /* for KVM_IRQ_LINE */
> >  struct kvm_irq_level {
> > -- 
> > 2.17.1
> >