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This flag collapses them to >> exactly one outstanding disable per SNP-active window, because the disable and enable >> sites are not reached a symmetric number of times: > > Well, why aren't they? > > Why isn't a simple design where on SNP init hotplug is disabled - *exactly* > one call to cpu_hotplug_disable() and on SNP shutdown hotplug is reenabled > again - also exactly one call. > > I know why... > It can be that simple, and flag-free, by following the SNP_EN state: - cpu_hotplug_disable() when SNP_EN is programmed: in snp_prepare(), before snp_enable(). - cpu_hotplug_enable() when SNP_EN is cleared: in snp_shutdown(), after the firmware clears it on X86_SNP_SHUTDOWN. SNP_EN is set only by snp_enable() in snp_prepare() (gated by online == present), and only the firmware clears it. So: - snp_prepare() programs SNP_EN and disables hotplug on the same path; if it's called again while SNP_EN is already set (re-init), it bails before the disable. - snp_shutdown() runs only on the X86_SNP_SHUTDOWN path, after SNP_EN has been cleared, and enables hotplug. A legacy shutdown leaves SNP_EN set and does not call snp_shutdown(), so hotplug correctly stays disabled. We also have to re-enable cpu hotplug on the init failure paths (snp_prepare()'s online != present check, and the SNP_INIT_EX / DF_FLUSH failures in __sev_snp_init_locked()), so a failed init leaves hotplug enabled, as it was before this support. The only extra case is a kexec target that boots with SNP_EN already set (legacy firmware -- on X86_SNP_SHUTDOWN firmware the full shutdown required before kexec clears SNP_EN, so the target re-inits normally). There snp_prepare() bails, so I do the disable once at boot in snp_rmptable_init() when SNP_EN is already set. That and the snp_prepare() disable can't both run -- SNP_EN is either already set at boot, or it gets programmed by snp_prepare(). No (extra) flag needed. Thanks, Ashish