Re: [PATCH v6 1/4] x86/ioreq server: Add HVMOP to map guest ram with p2m_ioreq_server to an ioreq server.

[George Dunlap <george.dunlap@citrix.com>]

On 05/09/16 14:31, Jan Beulich wrote:
>>>> On 02.09.16 at 12:47, <yu.c.zhang@linux.intel.com> wrote:
>> @@ -178,8 +179,27 @@ static int hvmemul_do_io(
>>          break;
>>      case X86EMUL_UNHANDLEABLE:
>>      {
>> -        struct hvm_ioreq_server *s =
>> -            hvm_select_ioreq_server(curr->domain, &p);
>> +        struct hvm_ioreq_server *s = NULL;
>> +        p2m_type_t p2mt = p2m_invalid;
>> +
>> +        if ( is_mmio )
>> +        {
>> +            unsigned long gmfn = paddr_to_pfn(addr);
>> +
>> +            (void) get_gfn_query_unlocked(currd, gmfn, &p2mt);
>> +
>> +            if ( p2mt == p2m_ioreq_server && dir == IOREQ_WRITE )
>> +            {
>> +                unsigned int flags;
>> +
>> +                s = p2m_get_ioreq_server(currd, &flags);
>> +                if ( !(flags & XEN_HVMOP_IOREQ_MEM_ACCESS_WRITE) )
>> +                    s = NULL;
>> +            }
>> +        }
>> +
>> +        if ( !s && p2mt != p2m_ioreq_server )
>> +            s = hvm_select_ioreq_server(currd, &p);
> 
> What I recall is that we had agreed on p2m_ioreq_server pages
> to be treated as ordinary RAM ones as long as no server can be
> found. The type check here contradicts that. Is there a reason?

I think it must be a confusion as to what "treated like ordinary RAM
ones" means.  p2m_ram_rw types that gets here will go through
hvm_select_ioreq_server(), and (therefore) potentially be treated as
MMIO accesses, which is not how "ordinary RAM" would behave.  If what
you meant was that you want p2m_ioreq_server to behave like p2m_ram_rw
(and be treated as MMIO if it matches an iorange) then yes.  If what you
want is for p2m_ioreq_server to actually act like RAM, then probably
something more needs to happen here.

 -George

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