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A malicious > + * hypervisor could lie about the C-bit position to perform a ROP > + * attack on the guest by writing to the unencrypted stack and wait for > + * the next RET instruction. > + */ > + call sev_verify_cbit > + > + /* > + * Restore CR3 value without the phys_base which will be added > + * below, before writing %cr3. > + */ > + mov %r14, %rax You're ignoring RAX now on return, so you can probably just make sev_verify_cbit() a void function now. You would still need to save RAX because of the calling convention, though, so it doesn't make this code any cleaner (other than the comment could then just say restore CR3 value). You're call, I'm good either way. Thanks, Tom > +#endif > + > jmp 1f > SYM_CODE_END(startup_64) > > @@ -192,15 +214,6 @@ SYM_INNER_LABEL(secondary_startup_64_no_verify, SYM_L_GLOBAL) > /* Setup early boot stage 4-/5-level pagetables. */ > addq phys_base(%rip), %rax > > - /* > - * For SEV guests: Verify that the C-bit is correct. A malicious > - * hypervisor could lie about the C-bit position to perform a ROP > - * attack on the guest by writing to the unencrypted stack and wait for > - * the next RET instruction. > - */ > - movq %rax, %rdi > - call sev_verify_cbit > - > /* > * Switch to new page-table > *