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SubjectRe: [PATCH v6 02/14] KVM: Cache as_id in kvm_memory_slot
On Tue, Mar 10, 2020 at 07:48:59AM -0700, Sean Christopherson wrote:
> On Mon, Mar 09, 2020 at 05:44:12PM -0400, Peter Xu wrote:
> > Cache the address space ID just like the slot ID. It will be used in
> > order to fill in the dirty ring entries.
> >
> > Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
> > Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> > include/linux/kvm_host.h | 1 +
> > virt/kvm/kvm_main.c | 2 ++
> > 2 files changed, 3 insertions(+)
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index bcb9b2ac0791..afa0e9034881 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -346,6 +346,7 @@ struct kvm_memory_slot {
> > unsigned long userspace_addr;
> > u32 flags;
> > short id;
> > + u8 as_id;
>
> My vote is to store this as a u16 and remove the BUILD_BUG_ON. Using a u8
> doesn't save any memory since the compiler will pad out the struct.

Sure. Indeed that BUILD_BUG_ON does not help much in this case. Thanks,

>
> > };
> >
> > static inline unsigned long kvm_dirty_bitmap_bytes(struct kvm_memory_slot *memslot)
> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 70f03ce0e5c1..e6484dabfc59 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -1036,6 +1036,8 @@ int __kvm_set_memory_region(struct kvm *kvm,
> >
> > new = old = *slot;
> >
> > + BUILD_BUG_ON(U8_MAX < KVM_ADDRESS_SPACE_NUM);
> > + new.as_id = as_id;
> > new.id = id;
> > new.base_gfn = base_gfn;
> > new.npages = npages;
> > --
> > 2.24.1
> >
>

--
Peter Xu

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