Re: [PATCH 1/4] KVM: MMU: Introduce drop_spte()

[Avi Kivity <avi@redhat.com>]

On 06/06/2010 04:06 PM, Avi Kivity wrote:
> When we call rmap_remove(), we (almost) always immediately follow it by
> an __set_spte() to a nonpresent pte.  Since we need to perform the two
> operations atomically, to avoid losing the dirty and accessed bits, introduce
> a helper drop_spte() and convert all call sites.
>
> The operation is still nonatomic at this point.
>
>
> @@ -1498,13 +1502,14 @@ static void kvm_mmu_page_unlink_children(struct kvm *kvm,
>   				ent&= PT64_BASE_ADDR_MASK;
>   				mmu_page_remove_parent_pte(page_header(ent),
>   							&pt[i]);
> +				pt[i] = shadow_trap_nonpresent_pte;
>   			} else {
>   				if (is_large_pte(ent))
>   					--kvm->stat.lpages;
> -				rmap_remove(kvm,&pt[i]);
> +				drop_spte(kvm,&pt[i],
> +					  shadow_trap_nonpresent_pte);
>   			}
>   		}
> -		pt[i] = shadow_trap_nonpresent_pte;
>   	}
>   }
>    

Autotest points out that this transformation (and an identical one in 
zap_pte) does not preserve the semantics; if the outer if () fails, the 
new code does not update pt[i].

With the original line after the if () retained, autotest is happier.

-- 
error compiling committee.c: too many arguments to function