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Re: [Xen-devel] RT Xen on ARM - R-Car series

On 04.02.19 13:36, Julien Grall wrote:
That's a good news! Let me try to address your concerns below one by one.
Lets do it:)

And they employ KPTI enabled kernel in the BSP.
KPTI is going to work on Xen. There are no known issue with Linux as the 
virtual address is not going to be re-used for other purpose in the virtual 
address space. The only inconvenience is the message in debug build.
Just in case, I am not saying it should not be fixed :).
We have a decision to eliminate it.

That reveals another critical issue for us, in addition to Set/Way issue

 From the discussion on the another thread and with other people, this is not 
entirely the fault of Xen. This was a misuse of the instructions by the driver.

Yep, but it is still on our team to solve.

While you may want to deal with this in your case, I would like to avoid 
promoting bad behavior when using Xen upstream.

Ah, ok. Will say that in different words.

and possible performance drops/irq latency raise due to specter mitigation 

Can you remind me the cores you are using?


I see the following in my log:

    (XEN) alternatives: Patching with alt table 00000000002c6608 -> 
    (XEN) CPU0 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
    (XEN) CPU2 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
    (XEN) CPU3 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
    (XEN) CPU1 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry

Also, when you mean possible, does it mean you haven't looked the performance 
We have a preliminary results about performance drop with xen4.12-unstable 
comparing to a our system with 4.10.
But those results are from Nov IIRC, and we have to recheck. After fixing 
Set/Way misuse in our proprietary driver ;)

I'm not sure if this is sufficient a justification to make it the release 
blocker, but we are up to this stuff.
Which one?

KPTI issue, as you suggested.

Andrii Anisov.

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