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Right here: >>> >>> /* CR4 should maintain the MCE value */ >>> cr4 = native_read_cr4() & X86_CR4_MCE; >>> >>> It's got to be some delta there. >> Looks the same to me: >> >> before: 31 SEV: wakeup_cpu_via_vmgexit: CR4: 0x3506f0 >> >> That's 31 CPUs - no BSP with the CR4 value above. >> >> after: [ 3.354326] SEV: wakeup_cpu_via_vmgexit: CR4: 0x3506f0 >> >> That stops after CPU1, i.e., the first AP. But the CR4 value is the same. > > The only pinned bits in there are: SMAP, SMEP and FSGSBASE. > > SMAP and SMEP are unlikely to be biting us here. > > FSGSBASE is _possible_ but I don't see any of the {RD,WR}{F,G}SBASE > instructions in early boot where it would bite us. > > Can you boot this thing without FSGSBASE support? > > The other option would be to boot a working system, normally and see > what is getting flipped by pinning at cr4_init(). The attached patch > does that. It also uses trace_printk() so it hopefully won't trip over > #VC's during early boot with the console. > > For me, it's flipping on 0x310800, which is: > > #define X86_CR4_OSXMMEXCPT (1ul << 10) > #define X86_CR4_FSGSBASE (1ul << 16) > #define X86_CR4_SMEP (1ul << 20) > #define X86_CR4_SMAP (1ul << 21) > > *Maybe* the paranoid entry code is getting called from the #VC handler > in early boot? It has ALTERNATIVEs on X86_FEATURE_FSGSBASE and might be > using the FSGSBASE instructions in there. Could be... before the patch the AP CR4 value is: [ 0.020362] *** DEBUG: cr4_init - cr4=0x3100f0 after the patch it is: [ 0.020284] *** DEBUG: cr4_init - cr4=0xf0 The SNP guest is dying in __x2apic_enable() when trying to read MSR_IA32_APICBASE, which will trigger a #VC. If I set CR4[16] in cr4_init() then the SNP guest boots fine. Thanks, Tom