On Tue, Feb 24, 2026 at 09:50:11AM -0800, Sean Christopherson wrote: > On Mon, Feb 23, 2026, Tycho Andersen wrote: > > On Mon, Feb 23, 2026 at 08:40:19AM -0800, Sean Christopherson wrote: > > > On Mon, Feb 23, 2026, Tycho Andersen wrote: > > > > From: "Tycho Andersen (AMD)" <[email protected]> > > > > > > > > The kernel allows setting the RAPL_DIS policy bit, but had no way to set > > > > > > Please actually say what RAPL_DIS is and does, and explain why this is the > > > correct approach. I genuinely have no idea what the impact of this patch > > > is, > > > (beyond disabling something, obviously). > > > > Sure, the easiest thing is probably to quote the firmware PDF: > > > > Some processors support the Running Average Power Limit (RAPL) > > feature which provides information about power utilization of > > software. RAPL can be disabled using the RAPL_DIS flag in > > SNP_INIT_EX to disable RAPL while SNP firmware is in the INIT > > state. Guests may require that RAPL is disabled by using the > > POLICY.RAPL_DIS guest policy flag. > > Ah, I assume this about disabling RAPL to mitigate a potential side channel? > If > so, please call that out in the changelog. > > And does this disable RAPL for _everything_? Or does it just disable RAPL for > SNP VMs? If it's the former, then burying this in > drivers/crypto/ccp/sev-dev.c > feels wrong.
Presumably you're right on both counts, but I've asked our firmware team to clarify exactly what happens. I guess that means it should be kvm-amd.rapl_disable? Thanks, Tycho
