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

[George Dunlap <george.dunlap@xxxxxxxxxxxxx>]

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.

 -G


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