Re: [Xen-devel] [PATCH v2 09/10] x86/irqs: Move interrupt-stub generation out of C

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.05.14 at 17:22, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 16/05/14 16:06, Jan Beulich wrote:
>>>>> On 16.05.14 at 12:39, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>>
>>>>>
>>> --- a/xen/arch/x86/x86_64/entry.S
>>> +++ b/xen/arch/x86/x86_64/entry.S
>>> @@ -475,6 +475,12 @@ ENTRY(common_interrupt)
>>>          callq do_IRQ
>>>          jmp ret_from_intr
>>>  
>>> +ENTRY(reserved_exception)
>>> +        SAVE_ALL CLAC
>>> +        movq %rsp,%rdi
>>> +        callq do_reserved_exception
>>> +        jmp ret_from_intr
>> Sadly this still doesn't take care of auto-detecting whether an error
>> code got pushed.
> 
> It is not supposed to.
> 
> Each reserved exception has its own automatically generated stub which
> pushes its trap value, so do_reserved_exception() can identify which
> trap has been unexpectedly triggered.
> 
> Currently there are no reserved exceptions which push an error code.  I
> will leave a warning comment by the generation code to take care with
> the first pushq $0.

The nature of reserved exceptions is that you don't know whether
they would push an error code. For instance, a year or two ago
(unless you were Intel) you wouldn't have known whether #VE
would have one.

>> Also - is there a particular reason you don't have this go though
>> handle_exception?
> 
> I hadn't considered that.  Its a good idea.  We can:
> 
> * Automatically generate the reserved entry point, directed at
> handle_exception
> * Fully populate the exception_table, with several labels going towards
> do_reserved_exception.
> * Treat the double fault entry in exception_table as reserved.  We
> certainly don't want to enter through it.

That sounds nice.

>>> @@ -717,13 +713,13 @@ ENTRY(exception_table)
>>>          .quad do_invalid_op
>>>          .quad do_device_not_available
>>>          .quad BAD_VIRT_ADDR         /* double_fault, IST entry */
>>> -        .quad do_coprocessor_segment_overrun
>>> +        .quad BAD_VIRT_ADDR         /* coproc_seg_overrun, reserved */
>>>          .quad do_invalid_TSS
>>>          .quad do_segment_not_present
>>>          .quad do_stack_segment
>>>          .quad do_general_protection
>>>          .quad do_page_fault
>>> -        .quad do_spurious_interrupt_bug
>>> +        .quad BAD_VIRT_ADDR         /* PIC IRQ7 spurious, reserved */
>> And the comment here didn't get much (if at all) adjusted either.
> 
> What about "Default PIC spurious interrupt, architecturally reserved" ?

Fine with me.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel