Re: [Xen-ia64-devel] alt_itlb_miss?

[Masaki Kanno <kanno.masaki@xxxxxxxxxxxxxx>]

Hi Kevin,

Thank for your explanation.

Tian, Kevin wrote:
>Hi, Kan,
>       Thanks for detail figure. From architecture correctness, I think
>your patch is yes required though case 2 is only walked before dom0 
>loads rr7 (After that, vhpt table will be enabled from then on and case 
>1 is the only path then).

I misunderstood about VHPT. When Xen code is running, I thought that 
VHPT was always disabled. Then, I also think that I have only to remove 
FORCE_CRASH from alt_itlb_miss.

Best regards,
 Kan

>       So please re-submit the patch again and it's better if you could 
>move the check to the point before late_alt_itlb_miss to avoid 
>duplicated check in case 2. Also, it's better to jump to page_fault 
>instead of crash the whole xen here which is over-killed. :-)
>
>Thanks,
>Kevin
>
>>-----Original Message-----
>>From: Masaki Kanno [mailto:kanno.masaki@xxxxxxxxxxxxxx]
>>Sent: 2006定4埖24晩 15:40
>>To: Tian, Kevin
>>Cc: Alex Williamson; Isaku Yamahata; xen-ia64-devel
>>Subject: Re: [Xen-ia64-devel] alt_itlb_miss?
>>
>>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協4・Q1賦 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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