Re: [PATCH v2 04/14] x86/traps: Implement #CP handler and extend #PF for shadow stacks

[Jan Beulich <jbeulich@xxxxxxxx>]

On 28.05.2020 15:22, Andrew Cooper wrote:
> On 28/05/2020 13:03, Jan Beulich wrote:
>> On 27.05.2020 21:18, Andrew Cooper wrote:
>>> @@ -940,7 +944,8 @@ autogen_stubs: /* Automatically generated stubs. */
>>>          entrypoint 1b
>>>  
>>>          /* Reserved exceptions, heading towards do_reserved_trap(). */
>>> -        .elseif vec == TRAP_copro_seg || vec == TRAP_spurious_int || (vec 
>>> > TRAP_simd_error && vec < TRAP_nr)
>>> +        .elseif vec == X86_EXC_CSO || vec == X86_EXC_SPV || \
>>> +                vec == X86_EXC_VE  || (vec > X86_EXC_CP && vec < TRAP_nr)
>> Adding yet another || here adds to the fragility of the entire
>> construct. Wouldn't it be better to implement do_entry_VE at
>> this occasion, even its handling continues to end up in
>> do_reserved_trap()? This would have the benefit of avoiding the
>> pointless checking of %spl first thing in its handling. Feel
>> free to keep the R-b if you decide to go this route.
> 
> I actually have a different plan, which deletes this entire clause, and
> simplifies our autogen sanity checking somewhat.
> 
> For vectors which Xen has no implementation of (for whatever reason),
> use DPL0, non-present descriptors, and redirect #NP[IDT] into
> do_reserved_trap().

Except that #NP itself being a contributory exception, if the such
covered exception is also contributory (e.g. #CP) or of page fault
class (e.g. #VE), we'd get #DF instead of #NP afaict.

Jan