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Sashiko AI review found 1 potential issue(s) to consider: >> - [High] x86/sev: CPU hotplug disablement bypassed on early kexec errors >> -- >> >> commit ac084f2d7188c520f2ee3ced2ab76e4c068df91f >> Author: Ashish Kalra >> >> x86/sev: Disable CPU hotplug while SNP is active >> >> This commit disables CPU hotplug when SNP is enabled to prevent SNP guest >> memory from being broken by CPUs coming online without the SnpEn bit set. >> It ties CPU hotplug to the SNP-enable bit, disabling it in snp_prepare() >> and re-enabling it in snp_shutdown() when SNP is disabled. It also >> explicitly disables CPU hotplug during kexec if SNP is already enabled. >> >>> diff --git a/arch/x86/virt/svm/sev.c b/arch/x86/virt/svm/sev.c >>> index cff285d8ad8e3..558f7924a3f85 100644 >>> --- a/arch/x86/virt/svm/sev.c >>> +++ b/arch/x86/virt/svm/sev.c >> >> [ ... ] >> >>> @@ -577,6 +582,8 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp"); >>> */ >>> int __init snp_rmptable_init(void) >>> { >>> + u64 val; >>> + >>> if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP))) >>> return -ENOSYS; >>> >>> @@ -586,6 +593,15 @@ int __init snp_rmptable_init(void) >>> if (!setup_rmptable()) >>> return -ENOSYS; >>> >>> + /* >>> + * On a kexec boot SNP may already be enabled (legacy firmware leaves >>> + * SnpEn set across shutdown), in which case snp_prepare() bails without >>> + * disabling CPU hotplug, so disable it here. >>> + */ >>> + rdmsrq(MSR_AMD64_SYSCFG, val); >>> + if (val & MSR_AMD64_SYSCFG_SNP_EN) >>> + cpu_hotplug_disable(); >> >> [Severity: High] >> If a kexec kernel boots into a system where the previous kernel left >> MSR_AMD64_SYSCFG_SNP_EN active, and an early initialization step fails >> (such as passing amd_iommu=off > > amd_iommu=off means no SNP. > >> on the kernel command line resulting in !amd_iommu_snp_en, or >> setup_rmptable() failing), > > The same happens in that case: > > if (snp_rmptable_init()) { > pr_warn("SNP: RMP initialization failed, SNP cannot be supported.\n"); > goto disable_snp; > ^^^^^^^^^^^ > > Does Sashiko not see that or somehow it ate a lot of credits so it cannot use > enough now to "swap in" the whole context... if that is the AI that is going > to destroy the world, then I'm not too worried. :) > > Or is my AI failing me right now? > > :-P > > Leaving in the rest. Right, agreed โ€” As you have pointed out, on any snp_rmptable_init() failure โ€” setup_rmptable() failing, !amd_iommu_snp_en (amd_iommu=off), etc. โ€” the caller does goto disable_snp and SNP is disabled entirely. Thanks, Ashish > >> snp_rmptable_init() will >> return -ENOSYS before checking the physical MSR hardware state and >> disabling CPU hotplug. >> >> Because hotplug remains enabled and the CCP driver skips initialization on >> failure (bypassing snp_prepare()), could a subsequently hotplugged CPU come >> online without the SNP_EN bit set? > > Yes, but the above disabled all our intention of running SNP in the first > place... > >> If this results in a mixed hardware state, does it violate firmware >> constraints and cause fatal RMP faults when the new CPU accesses memory? >> >> Should the hardware state be checked and hotplug disabled unconditionally >> before the software configuration checks? >> >> -- >> Sashiko AI review ยท https://sashiko.dev/#/patchset/cover.1789594774.git.ashish.kalra@amd.com?part=2 >