Re: [Xen-devel] [PATCH] xen: Restore p2m_access_t enum order to allow bitmask semantics

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Tue, Mar 8, 2016 at 4:52 PM, Jan Beulich <JBeulich@xxxxxxxx> wrote:

>>> On 08.03.16 at 16:30, <malcolm.crossley@xxxxxxxxxx> wrote:
> Nested hap code assumed implict bitmask semantics of the p2m_access_t
> enum prior to C/S 4c63692d7c38c5ac414fe97f8ef37b66e05abe5c
>
> The change to the enum ordering broke this assumption and caused functional
> problems for the nested hap code. As it may be error prone to audit and find
> all other p2m_access users assuming bitmask semantics, instead restore the
> previous enum order and make it explict that bitmask semantics are to be
> preserved for the read, write and execute access types.

Makes sense, but how certain are you that ...

> --- a/xen/include/xen/p2m-common.h
> +++ b/xen/include/xen/p2m-common.h
> @@ -15,14 +15,15 @@
>   * default.
>   */
>  typedef enum {
> -    p2m_access_rwx   = 0, /* The default access type when not used. */

... namely this has not meanwhile seen any implicit use somewhere?

Tamas, the original commit talked about this as an optimization only.
Can you confirm that there indeed was no other intention than the
one claimed in that commit's description?

That's the only reason I recall as well, so from my perspective it's fine to be reverted.

Tamas

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel