Re: [Qemu-devel] [PATCH v2] exec: fix address_space_get_iotlb_entry page mask

[Paolo Bonzini <pbonzini@redhat.com>]

On 29/05/2017 06:02, Peter Xu wrote:
> The IOTLB that it returned didn't guarantee that page_mask is indeed a
> so-called page mask. That won't affect current usage since now only
> vhost is using it (vhost API allows arbitary IOTLB range). However we
> have IOTLB scemantic and we should best follow it. This patch fixes this
> issue to make sure the page_mask is always a valid page mask.
> 
> Fixes: a764040 ("exec: abstract address_space_do_translate()")
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
> Sorry please use this one. The codes is merely the same, just avoided
> moving the codes around unnecessarily.
> ---
>  exec.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/exec.c b/exec.c
> index ff16f04..3db247c 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -529,16 +529,14 @@ IOMMUTLBEntry address_space_get_iotlb_entry(AddressSpace *as, hwaddr addr,
>          section.offset_within_region;
>  
>      if (plen == (hwaddr)-1) {
> -        /*
> -         * We use default page size here. Logically it only happens
> -         * for identity mappings.
> -         */
> -        plen = TARGET_PAGE_SIZE;
> +        /* If not specified during translation, use default mask */
> +        plen = TARGET_PAGE_MASK;
> +    } else {
> +        /* Make it a valid page mask */
> +        assert(plen);
> +        plen = (1ULL << (63 - clz64(plen))) - 1;

Would pow2floor be better?

Thanks,

Paolo

>      }
>  
> -    /* Convert to address mask */
> -    plen -= 1;
> -
>      return (IOMMUTLBEntry) {
>          .target_as = section.address_space,
>          .iova = addr & ~plen,
>