[PATCH v4 2/7] arm64: KVM: Use shared area to pass PMU event state to hypervisor

[James Clark]

On 05/02/2024 13:21, Oliver Upton wrote:
> On Mon, Feb 05, 2024 at 01:15:36PM +0000, Marc Zyngier wrote:
>> On Mon, 05 Feb 2024 13:04:51 +0000,
>> Oliver Upton <oliver.upton at linux.dev> wrote:
>>>
>>> Unless someone has strong opinions about making this work in protected
>>> mode, I am happy to see tracing support limited to the 'normal' nVHE
>>> configuration. The protected feature as a whole is just baggage until
>>> upstream support is completed.
>>
>> Limiting tracing to non-protected mode is a must IMO. Allowing tracing
>> when pKVM is enabled is a sure way to expose secrets that should
>> stay... secret. The only exception I can think of is when
>> CONFIG_NVHE_EL2_DEBUG is enabled, at which point all bets are off.
> 
> Zero argument there :) I left off the "and PMU" part of what I was
> saying, because that was a feature that semi-worked in protected mode
> before VM/VCPU shadowing support landed.
> 

In that case I can hide all this behind CONFIG_NVHE_EL2_DEBUG for pKVM.
This will also have the effect of disabling PMU again for pKVM because I
moved that into this new shared area.

The same place will be used to store the state for normal nVHE and at
least then there is some code re-use and flexibility to use trace and
PMU for debugging if needed. And the copy on every switch gets deleted.