Re: KVM: MMU: bail out pagewalk on kvm_read_guest error

[Avi Kivity <avi@redhat.com>]

On 01/14/2010 09:41 PM, Marcelo Tosatti wrote:
> Exit the guest pagetable walk loop if reading gpte failed. Otherwise its
> possible to enter an endless loop processing the previous present pte.
>
> Cc: stable@kernel.org
> Signed-off-by: Marcelo Tosatti<mtosatti@redhat.com>
>
> diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
> index 58a0f1e..ede2131 100644
> --- a/arch/x86/kvm/paging_tmpl.h
> +++ b/arch/x86/kvm/paging_tmpl.h
> @@ -150,7 +150,9 @@ walk:
>   		walker->table_gfn[walker->level - 1] = table_gfn;
>   		walker->pte_gpa[walker->level - 1] = pte_gpa;
>
> -		kvm_read_guest(vcpu->kvm, pte_gpa,&pte, sizeof(pte));
> +		if (kvm_read_guest(vcpu->kvm, pte_gpa,&pte, sizeof(pte)))
> +			goto not_present;
> +
>    

On real hardware, if you place a pte at non-existing memory, you aren't 
guaranteed to get the present bit clear, so why is this necessary?

We should be able to survive any garbage the pte previously contained.

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