Re: [Xen-ia64-devel] alt_itlb_miss?

[Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>]

Hi Kevin,

Thanks for your explanation. 
Sorry, I'd like you to explain this once again. Please look at the 
below figure.

1) Instruction TLB Fault ---+
                            |
     +----------------------+
     |
     +---> ENTRY(iltb_miss)
                /* Check ifa (It was VHPT_CCHAIN_LOOKUP before here) */
                mov r16 = cr.ifa
                extr.u r17=r16,59,5
                cmp.eq p6,p0=0x1e,r17
           (p6) br.cond.spnt late_alt_itlb_miss -----+
                cmp.eq p6,p0=0x1d,r17                |
           (p6) br.cond.spnt late_alt_itlb_miss ---+ |
                                                   | |
                                                   | |
2) Alternate Instruction TLB Fault ---+            | |
                                      |            | |
     +--------------------------------+            | |
     |                                             | |
     +---> ENTRY(alt_itlb_miss)                    | |
                mov r16=cr.ifa                     | |
                                                   | |
           late_alt_itlb_miss: <-------------------+-+

                /* Check cpl */
                cmp.ne p8,p0=r0,r23
                or r19=r17,r19
                or r19=r19,r18
           (p8) br.cond.spnt page_fault

      +         /* Check ifa with my patch */
      +         extr.u r22=r16,59,5
      +         cmp.ne p8,p0=0x1e,r22
      +    (p8) br.cond.spnt 1f ----------+
                                          |
                itc.i r19                 |
                mov pr=r31,-1             |
                rfi                       |
                                          |
      +    1: <---------------------------+
      +         FORCE_CRASH

If case 1), I think that a FORCE_CRASH and ifa checking is unnecessary 
according to your explanation.
If case 2), I think that a FORCE_CRASH and ifa checking is necessary.
Because, I thought that Xen may use a wrong address. 
If case 2), does Xen trust only cpl?

Best regards,
 Kan

Tian, Kevin wrote:
>>From: Masaki Kanno [mailto:kanno.masaki@xxxxxxxxxxxxxx]
>>Sent: 2006定4埖21晩 18:56
>>>>
>>>>Hi Kan,
>>>>
>>>>   Thanks, this looks like exactly what we need.  If there are no
>>other
>>>>comments, please send me this patch w/ a Signed-off-by and we can
>>get
>>>>it
>>>>in tree.  BTW, glad to hear you're working on the FPSWA issue and
>>are
>>>>making good progress!  Thanks,
>>>>
>>>>    Alex
>>>
>>>Seems OK. One small comment is that we may also remove
>>>FORCE_CRASH completely since the assumption to add that
>>>check doesn't exist now. Actually VHPT_CCHAIN_LOOKUP
>>>already makes check upon VMM area to decide whether jumping
>>>to alt_itlb_miss handler. In this case, simply removing
>>>FORCE_CRASH line can also work. :-)
>>
>>If alt_itlb_fault occurred, we need ifa checking and FORCE_CRASH,
>>don't we?
>>Therefore I don't need to change my patch, do I?
>>
>
>The check is already made before jumping to alt_itlb_miss. 
>Also architecturally there's no limitation to prevent uncacheable 
>instruction falling into that category. So I think there's no need 
>for existence of FORCE_CRASH there, right? :-)
>
>Thanks,
>Kevin
>


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