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

[Chao Peng]

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
> >