On 05/02/2024 14:52, Marc Zyngier wrote:
On Mon, 05 Feb 2024 14:17:10 +0000, James Clark james.clark@arm.com wrote:
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@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.
I'm not sure what you have in mind, but dropping PMU support for non-protected guests when protected-mode is enabled is not an acceptable outcome.
Hiding the trace behind a debug option is fine as this is a global setting that has no userspace impact, but impacting guests isn't.
M.
Hmmm in that case if there's currently no way to distinguish between normal VMs and pVMs in protected-mode then what I was thinking of probably won't work.
I'll actually just leave PMU as it is and only have tracing disabled in protected-mode.
My only question now is whether to:
* Keep this new shared area and use it for both PMU and trace status (well, for PMU only in protected mode as trace would always be disabled and doesn't actually need any state)
* Delete patch 2, add a new normal per-cpu struct just for trace status that's only used in non-protected mode and revert to copying the PMU status into the vCPU on guest switch as it was previously.
-
James Clark