Re: [Xen-devel] [PATCH 20/22] arch/x86: use XSM hooks for get_pg_owner access checks

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

On 09/13/2012 04:13 AM, Jan Beulich wrote:
>>>> On 12.09.12 at 17:59, Daniel De Graaf <dgdegra@xxxxxxxxxxxxx> wrote:
>> @@ -3353,9 +3357,14 @@ long do_mmu_update(
>>              mfn = req.ptr >> PAGE_SHIFT;
>>              gpfn = req.val;
>>  
>> -            rc = xsm_mmu_machphys_update(d, pg_owner, mfn);
>> -            if ( rc )
>> -                break;
>> +            xsm_needed |= XSM_MMU_MACHPHYS_UPDATE;
>> +            if ( xsm_needed != xsm_checked )
>> +            {
>> +                rc = xsm_mmu_update(d, pt_owner, pg_owner, xsm_needed);
> 
> If you're already updating it this way, it would seem appropriate
> to remove the over-checking here: pt_owner is meaningless for
> this operation (there are no page tables involved), and hence
> you could/should pass d instead.
> 
> Jan
> 

While this is safe, it makes thinking about the arguments to the XSM hook
harder: the second argument would be defined as "pt_owner if called with
XSM_MMU_NORMAL_UPDATE set and either XSM_MMU_MACHPHYS_UPDATE unset or
XSM_MMU_MACHPHYS_UPDATE set in the previous call; otherwise, d." I would
prefer the simpler method of passing pt_owner every time, and only checking
it if XSM_MMU_NORMAL_UPDATE is set (which I now notice that the default
XSM hook does not do, although the FLASK hook does; I'll fix that).

-- 
Daniel De Graaf
National Security Agency

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