Re: [PATCH] xen/arm64: Zero the top 32 bits of gp registers on entry...

[Michal Orzel <michal.orzel@xxxxxxx>]

Hi Julien,

On 15.12.2021 19:25, Julien Grall wrote:
> Hi Michal,
> 
> On 15/12/2021 10:40, Michal Orzel wrote:
>> On 15.12.2021 11:32, Jan Beulich wrote:
>>> (Re-sending an abridged version, as apparently spam filters didn't like
>>> the original message with more retained context; I'll have to see whether
>>> this one also isn't liked. Sorry.)
>>>
>>> On 15.12.2021 10:48, Michal Orzel wrote:
>>>> This patch and the problem it solves is about clearing top 32bits of all 
>>>> gp registers so not only x0,x1.
>>>
>>> That's well understood. Yet for everything still in registers simply
>>> using mov ahead of the respective push (as you had it) is still
>>> preferable imo.
>>>
>>> Jan
>>>
>>
>> In that case let's wait for Julien's opinion to decide whether I should get 
>> back to the previous
>> solution with mov or to the stack solution.
> 
> IIUC, your proposal is to:
>    1) Push all the 64-bit registers
>    2) Zero the top 32-bit
> 
> Jan's suggestion is to:
>    1) clobber the top 32-bit using mov wX, wX
>    2) Push all the registers
> 
> My preference is for the latter because there will be less memory/cache 
> access.
> 
> So, this would be your original patch + a compile time check to ensure 
> save_x0_x1 is 0 when compat=1.
> 
That is exactly what I would like to do. I will send this as v2.

> Cheers,
> 

Cheers,
Michal