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McKenney" , linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org References: <20260427204847.112899-1-tycho@kernel.org> <20260427204847.112899-4-tycho@kernel.org> <20f94bed-2843-44ab-877c-3e68bd4314f8@amd.com> Content-Language: en-US From: Tom Lendacky Autocrypt: addr=thomas.lendacky@amd.com; keydata= xsFNBFaNZYkBEADxg5OW/ajpUG7zgnUQPsMqWPjeAxtu4YH3lCUjWWcbUgc2qDGAijsLTFv1 kEbaJdblwYs28z3chM7QkfCGMSM29JWR1fSwPH18WyAA84YtxfPD8bfb1Exwo0CRw1RLRScn 6aJhsZJFLKyVeaPO1eequEsFQurRhLyAfgaH9iazmOVZZmxsGiNRJkQv4YnM2rZYi+4vWnxN 1ebHf4S1puN0xzQsULhG3rUyV2uIsqBFtlxZ8/r9MwOJ2mvyTXHzHdJBViOalZAUo7VFt3Fb aNkR5OR65eTL0ViQiRgFfPDBgkFCSlaxZvc7qSOcrhol160bK87qn0SbYLfplwiXZY/b/+ez 0zBtIt+uhZJ38HnOLWdda/8kuLX3qhGL5aNz1AeqcE5TW4D8v9ndYeAXFhQI7kbOhr0ruUpA udREH98EmVJsADuq0RBcIEkojnme4wVDoFt1EG93YOnqMuif76YGEl3iv9tYcESEeLNruDN6 LDbE8blkR3151tdg8IkgREJ+dK+q0p9UsGfdd+H7pni6Jjcxz8mjKCx6wAuzvArA0Ciq+Scg hfIgoiYQegZjh2vF2lCUzWWatXJoy7IzeAB5LDl/E9vz72cVD8CwQZoEx4PCsHslVpW6A/6U NRAz6ShU77jkoYoI4hoGC7qZcwy84mmJqRygFnb8dOjHI1KxqQARAQABzSZUb20gTGVuZGFj a3kgPHRob21hcy5sZW5kYWNreUBhbWQuY29tPsLBmQQTAQoAQwIbIwcLCQgHAwIBBhUIAgkK CwQWAgMBAh4BAheAAhkBFiEE3Vil58OMFCw3iBv13v+a5E8wTVMFAmkbaKgFCRZQah8ACgkQ 3v+a5E8wTVPFyg//UYANiuHfxxJET8D6p/vIV0xYcf1SXCG78M+5amqcE/4cCIJWyAT3A1nP zwyQIaIjUlGsXQtNgC1uVteCnMNJCjVQm0nLlJ9IVtXxzRg0QKjuSdZxuL5jrIon4xW9hTJR 94i2v3Fx5UWyP2TB6qZOcB0jgh0l01GHF9/DVJbmQlpvQB4Z1uNv09Q7En6EXi28TSv0Ffd1 p8vKqxwz7CMeAeZpn5i7s1QE/mQtdkyAmhuGD12tNbWzFamrDD1Kq3Em4TIFko0+k5+oQAAf JFaZc1c0D4GtXwvv4y+ssI0eZuOBXapUHeNNVf3JGuF6ZPLNPAe5gMQrmsJinEArVYRQCuDA BZakbKw9YJpGhnSVeCl2zSHcVgXuDs4J2ONxdsGynYv5cjPb4XTYPaE1CZH7Vy1tqma8eErG rcCyP1seloaC1UQcp8UDAyEaBjh3EqvTvgl+SppHz3im0gPJgR9km95BA8iGx9zqDuceATBc +A007+XxdFIsifMGlus0DKPmNAJaLkEEUMedBBxH3bwQ+z8tmWHisCZQJpUeGkwttD1LK/xn KRnu8AQpSJBB2oKAX1VtLRn8zLQdGmshxvsLUkKdrNE6NddhhfULqufNBqul0rrHGDdKdTLr cK5o2dsf9WlC4dHU2PiXP7RCjs1E5Ke0ycShDbDY5Zeep/yhNWLOwU0EVo1liQEQAL7ybY01 hvEg6pOh2G1Q+/ZWmyii8xhQ0sPjvEXWb5MWvIh7RxD9V5Zv144EtbIABtR0Tws7xDObe7bb r9nlSxZPur+JDsFmtywgkd778G0nDt3i7szqzcQPOcR03U7XPDTBJXDpNwVV+L8xvx5gsr2I bhiBQd9iX8kap5k3I6wfBSZm1ZgWGQb2mbiuqODPzfzNdKr/MCtxWEsWOAf/ClFcyr+c/Eh2 +gXgC5Keh2ZIb/xO+1CrTC3Sg9l9Hs5DG3CplCbVKWmaL1y7mdCiSt2b/dXE0K1nJR9ZyRGO lfwZw1aFPHT+Ay5p6rZGzadvu7ypBoTwp62R1o456js7CyIg81O61ojiDXLUGxZN/BEYNDC9 n9q1PyfMrD42LtvOP6ZRtBeSPEH5G/5pIt4FVit0Y4wTrpG7mjBM06kHd6V+pflB8GRxTq5M 7mzLFjILUl9/BJjzYBzesspbeoT/G7e5JqbiLWXFYOeg6XJ/iOCMLdd9RL46JXYJsBZnjZD8 Rn6KVO7pqs5J9K/nJDVyCdf8JnYD5Rq6OOmgP/zDnbSUSOZWrHQWQ8v3Ef665jpoXNq+Zyob pfbeihuWfBhprWUk0P/m+cnR2qeE4yXYl4qCcWAkRyGRu2zgIwXAOXCHTqy9TW10LGq1+04+ LmJHwpAABSLtr7Jgh4erWXi9mFoRABEBAAHCwXwEGAEKACYCGwwWIQTdWKXnw4wULDeIG/Xe /5rkTzBNUwUCaRto5wUJFlBqXgAKCRDe/5rkTzBNUw4/EAClG106SeHXiJ+ka6aeHysDNVgZ 8pUbB2f8dWI7kzD5AZ5kLENnsi1MzJRYBwtg/vVVorZh6tavUwcIvsao+TnV57gXAWr6sKIc xyipxRVEXmHts22I6vL1DirLAoOLAwWilkM+JzbVE3MMvC+cCVnMzzchrMYDTqn1mjCCwiIe u5oop+K/RgeHYPsraumyA9/kj8iazrLM+lORukCNM7+wlRClcY8TGX+VllANym9B6FMxsJ5z Q7JeeXIgyGlcBRME+m3g40HfIl+zM674gjv2Lk+KjS759KlX27mQfgnAPX4tnjLcmpSQJ77I Qg+Azi/Qloiw7L/WsmxEO5ureFgGIYDQQUeM1Qnk76K5Z3Nm8MLHtjw3Q7kXHrbYn7tfWh4B 7w5Lwh6NoF88AGpUrosARVvIAd93oo0B9p40Or4c5Jao1qqsmmCCD0dl7WTJCboYTa2OWd99 oxS7ujw2t1WMPD0cmriyeaFZnT5cjGbhkA+uQGuT0dMQJdLqW3HRwWxyiGU/jZUFjHGFmUrj qFAgP+x+ODm6/SYn0LE0VLbYuEGfyx5XcdNnSvww1NLUxSvuShcJMII0bSgP3+KJtFqrUx9z l+/NCGvn/wMy6NpYUpRSOmsqVv0N71LbtXnHRrJ42LzWiRW2I5IWsb1TfdMAyVToHPNaEb0i WiyqywZI5g== In-Reply-To: Content-Type: text/plain; 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That needs to be a power management thing. >>>> >>>> You definitely noted "not CCP", I don't think I quite understood what >>>> that meant though: >>>> https://lore.kernel.org/all/aZ86BZWi-GLiHvmt@tycho.pizza/ >>>> >>>> I'm a little worried that putting it in power management will generate >>>> some weird dependencies, or weakref symbols that can't change things >>>> if they are loaded independently of kvm_amd or something. But let me >>>> see what I can come up with. >>> >>> Ugh, and it's not even powerman per se, it's actually a module in perf. Oof. >>> >>> I 100% agree it'll be tricky, but I also stand by comments that neither the CCP >>> driver or KVM should be allowed to silently pull the rug out from under the RAPL >>> module. >> >> Maybe something that can be added to the current sev= kernel command line >> parameter, e.g. sev=norapl, or such? > > Yeah. The only question I have is if we expect end users to want to disable RAPL > at runtime. If so, then we probably want a sysfs knob or something. > > However, letting RAPL be toggled on/off will introduce some amount of complexity, > as the kernel would need to negotiate/coordinate with the RAPL perf module and > with the CPP driver to ensure RAPL stays in the "correct" state. E.g. if the > perf module is loaded, then RAPL is effectively pinned "on". And if SNP has been > initialized with RAPL_DIS, then RAPL is effectively pinned "off". Blech. > >> Maybe even with a kernel config option for a default value? > > Probably overkill? Yeah, probably. > >> On SNP_SHUTDOWN it will be re-enabled if it was disabled. > > Stating the obvious, if we do this, we open the can of worms I described above. > >>>>> KVM then needs to communicate (and enforce?) the policy to >>>>> userspace. >>>> >>>> KVM doesn't need to enforce anything, the SEV firmware will generate a >>>> launch error for policy violation if it's not supported. >>>> >>>> For communicating to userspace if it's not a kvm module parameter, one >>>> option is to mask it off in sev_get_snp_supported_policy() if it was >> >> Did you mean sev_get_snp_policy_bits() or were you referring to the KVM >> ioctl() for retrieving them? >> >>>> initialized without the support. Then it'll be visible via >>>> KVM_X86_SNP_POLICY_BITS. >>> >>> Ya, this is what I was envisioning. >> >> It's still a valid policy bit (if supported by the platform), so I don't >> think masking it off is appropriate. > > But it's not fully supported, no? I.e. won't the VM fail if it requests RAPL_DIS? > > Ooh, presumably the subtle difference is that on a platform without RAPL_DIS at > all, the VM will successfully launch and thus could run with RAPL enabled even > if the VM requested RAPL_DIS? No, the VM launch will fail in that case, too. But I thought the difference there would be getting an INVALID_PARAM for specifying an unsupported policy bit, but I think you still get POLICY_FAILURE, so maybe it doesn't matter. Thanks, Tom