Re: [Xen-devel] [PATCH v4 08/15] x86/altp2m: add control of suppress_ve.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.07.15 at 13:11, <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 07/10/2015 10:39 AM, Jan Beulich wrote:
>>>>> On 10.07.15 at 02:52, <edmund.h.white@xxxxxxxxx> wrote:
>>> @@ -1528,16 +1528,17 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned 
>>> long gla,
>>>      vm_event_request_t *req;
>>>      int rc;
>>>      unsigned long eip = guest_cpu_user_regs()->eip;
>>> +    bool_t sve;
>>>  
>>>      /* First, handle rx2rw conversion automatically.
>>>       * These calls to p2m->set_entry() must succeed: we have the gfn
>>>       * locked and just did a successful get_entry(). */
>>>      gfn_lock(p2m, gfn, 0);
>>> -    mfn = p2m->get_entry(p2m, gfn, &p2mt, &p2ma, 0, NULL);
>>> +    mfn = p2m->get_entry(p2m, gfn, &p2mt, &p2ma, 0, NULL, &sve);
>>>  
>>>      if ( npfec.write_access && p2ma == p2m_access_rx2rw ) 
>>>      {
>>> -        rc = p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2mt, 
>>> p2m_access_rw);
>>> +        rc = p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K, p2mt, 
>>> p2m_access_rw, sve);
>>>          ASSERT(rc == 0);
>>>          gfn_unlock(p2m, gfn, 0);
>>>          return 1;
>>> @@ -1546,7 +1547,7 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned 
>>> long gla,
>>>      {
>>>          ASSERT(npfec.write_access || npfec.read_access || 
>>> npfec.insn_fetch);
>>>          rc = p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K,
>>> -                            p2mt, p2m_access_rwx);
>>> +                            p2mt, p2m_access_rwx, -1);
>> 
>> So why -1 here ...
>> 
>>> @@ -1566,14 +1567,14 @@ bool_t p2m_mem_access_check(paddr_t gpa, unsigned 
>>> long gla,
>>>          else
>>>          {
>>>              gfn_lock(p2m, gfn, 0);
>>> -            mfn = p2m->get_entry(p2m, gfn, &p2mt, &p2ma, 0, NULL);
>>> +            mfn = p2m->get_entry(p2m, gfn, &p2mt, &p2ma, 0, NULL, &sve);
>>>              if ( p2ma != p2m_access_n2rwx )
>>>              {
>>>                  /* A listener is not required, so clear the access
>>>                   * restrictions.  This set must succeed: we have the
>>>                   * gfn locked and just did a successful get_entry(). */
>>>                  rc = p2m->set_entry(p2m, gfn, mfn, PAGE_ORDER_4K,
>>> -                                    p2mt, p2m_access_rwx);
>>> +                                    p2mt, p2m_access_rwx, sve);
>> 
>> ... but sve here, when -1 means "retain current setting" anyway?
>> (Same question applies elsewhere.)
> 
> This is my code. I considered whether to use -1 here, but since we're
> reading and retaining gfn, mfn, and p2mt, it seemed more consistent
> stylistically to just read and re-write it along with the others.
> 
> In any case I don't have strong opinions.

I'd suggest the other mechanism so one can easily see which places
actually want to change the flag (or set it to a specific value). But in
the end it's your call which way to go.

Jan


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