Messages in this thread | | | Date | Mon, 05 Feb 2024 15:50:12 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v4 2/7] arm64: KVM: Use shared area to pass PMU event state to hypervisor |
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On Mon, 05 Feb 2024 15:37:34 +0000, James Clark <james.clark@arm.com> wrote: > > > > 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.
Have you looked? kvm_vm_is_protected() has been in for a while, even if that's not a lot. The upcoming code will flesh this helper out,
M.
-- Without deviation from the norm, progress is not possible.
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