linux-kernel - Re: [RFC PATCH] kvm: nv: Optimize the unmapping of shadow S2-MMU tables.

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Date: Tue, 26 Mar 2024 17:03:27 +0530
From: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
To: Marc Zyngier <maz@...nel.org>
Cc: kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 oliver.upton@...ux.dev, darren@...amperecomputing.com,
 d.scott.phillips@...erecomputing.com
Subject: Re: [RFC PATCH] kvm: nv: Optimize the unmapping of shadow S2-MMU
 tables.

Hi Marc,

On 05-03-2024 08:33 pm, Marc Zyngier wrote:
> On Tue, 05 Mar 2024 13:29:08 +0000,
> Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com> wrote:
>>
>>
>>
>> What are the core issues (please forgive me if you mentioned already)?
>> certainly we will prioritise them than this.
> 
> AT is a big one. Maintenance interrupts are more or less broken. I'm
> slowly plugging PAuth, but there's no testing whatsoever (running
> Linux doesn't count). Lack of SVE support is also definitely a
> blocker.
> 

I am debugging an issue where EDK2(ArmVirtPkg) boot hangs when tried to 
boot from L1 using QEMU.

The hang is due to failure of AT instruction and resulting in immediate 
return to Guest(L2) and the loop continues...

AT instruction is executed in function of 
__get_fault_info(__translate_far_to_hpfar) in L1 when data abort is 
forwarded. Then AT instruction is trapped and executed/emulated in L0 in 
function "__kvm_at_s1e01" is failing and resulting in the return to guest.

Is this also the manifestation of the issue of AT that you are referring to?

Thanks,
Ganapat