linux-kernel - Re: [PATCH v10 02/14] KVM: Cache as_id in kvm_memory

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Date:   Thu, 2 Jul 2020 16:08:49 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Peter Xu <peterx@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Andrew Jones <drjones@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>
Subject: Re: [PATCH v10 02/14] KVM: Cache as_id in kvm_memory_slot

On Mon, Jun 01, 2020 at 07:59:45AM -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@...hat.com>
> Suggested-by: Sean Christopherson <sean.j.christopherson@...el.com>
> Signed-off-by: Peter Xu <peterx@...hat.com>
> ---
>  include/linux/kvm_host.h | 1 +
>  virt/kvm/kvm_main.c      | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 01276e3d01b9..5e7bbaf7a36b 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;
> +	u16 as_id;
>  };
>  
>  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 74bdb7bf3295..ebdd98a30e82 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -1243,6 +1243,7 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  	if (!mem->memory_size)
>  		return kvm_delete_memslot(kvm, mem, &old, as_id);

This technically needs to set as_id in the deleted memslot.  I highly doubt
it will ever matter from a functionality perspective, but it'd be confusing
to encounter a memslot whose as_id did not match that of its owner.

> +	new.as_id = as_id;
>  	new.id = id;
>  	new.base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
>  	new.npages = mem->memory_size >> PAGE_SHIFT;
> -- 
> 2.26.2
>