Re: [kvm-unit-tests PATCH] arm64: Make vector_table and vector_stub weak symbols

[Nikos Nikoleris <nikos.nikoleris@arm.com>]

On 23/05/2023 09:56, Andrew Jones wrote:
> On Mon, May 22, 2023 at 02:54:14PM +0100, Nikos Nikoleris wrote:
>> On 18/05/2023 17:06, Andrew Jones wrote:
>>> On Mon, May 15, 2023 at 11:15:17PM +0100, Nikos Nikoleris wrote:
>>>> This changes allows a test to define and override the declared symbols,
>>>> taking control of the whole vector_table or a vector_stub.
>>>
>>> Hi Nikos,
>>>
>>> Can you add some motivation for this change to the commit message or
>>> submit it along with some test that needs it?
>>>
>>
>> Hi Drew,
>>
>> Thanks for reviewing this.
>>
>> What do you think about adding the following to the commit message?
>>
>>> With the ability to override specific exception handlers, litmus7
>>> [1] a tool used to generate c sources for a given memory model
>>> litmus test, can override the el1h_sync symbol to implement tests
>>> with explicit exception handlers. For example:
>>>
>>> AArch64 LDRv0+I2V-dsb.ishst
>>> { >   [PTE(x)]=(oa:PA(x),valid:0);
>>>    x=1;
>>>
>>>    0:X1=x;
>>>    0:X3=PTE(x); >   0:X2=(oa:PA(x),valid:1);
>>> }>  P0          | P0.F         ;
>>> L0:          | ADD X8,X8,#1 ;
>>>   LDR W0,[X1] | STR X2,[X3]  ;
>>>               | DSB ISHST    ;
>>>               | ERET         ; > exists(0:X0=0 \/ 0:X8!=1)
>>>
>>> In this test, a thread running in core P0 executes a load to a memory
>>> location x. The PTE of the virtual address x is initially invalid.
>>> The execution of the load causes a synchronous EL1 exception which is
>>> handled by the code in P0.F. P0.F increments a counter which is
>>> maintained in X8, updates the PTE of x and makes it valid, executes a
>>> DSB ISHST and calls ERET which is expected to return and retry the
>>> execution of the load in P0:L0.
>>>
>>> The postcondition checks if there is any execution where the load wasn't
>>> executed (X0 its destination register is not update), or that the P0.F >
>>> handler was invoked more than once (the counter X8 is not 1).
>>>
>>> For this tests, litmus7 needs to control the el1h_sync. Calling
>>> install_exception_handler() would be suboptimal because the vector_stub
>>> would wrap around the code of P0.F and disturb the test.
>>>
>>> [1]: https://diy.inria.fr/doc/litmus.html
>> If you think this is sufficient, I will update the patch.
> 
> The above works for me.
> 
> (Unrelated: Sorry I haven't had a chance to give your latest efi branch
> a test drive. I think you can probably go ahead and post the next version
> of the series, though. That'll help bring it to the forefront for me to
> prioritize.)
> 

Thanks Drew, I'll send a new revision of this patch and the EFI series.

Nikos