On Sat, May 11, 2024 at 09:24:12AM +0800, Li, Xin3 wrote: >> >+/* >> >+ * It's enough to check just CR4.FRED (X86_CR4_FRED) to tell if >> >+ * a vCPU is running with FRED enabled, because: >> >+ * 1) CR4.FRED can be set to 1 only _after_ IA32_EFER.LMA = 1. >> >+ * 2) To leave IA-32e mode, CR4.FRED must be cleared first. >> >+ * >> >+ * More details at FRED Spec 6.0 Section 4.2 Enabling in CR4. >> >+ */ >> >> I think we can give more context here, e.g., >> >> Although FRED architecture applies to 64-bit mode only, there is no need to check if >> the CPU is in 64-bit mode (i.e., IA32_EFER.LMA and CS.L) to tell if FRED is enabled >> because CR4.FRED=1 implies the CPU is in 64-bit mode. > >What is "more context" here? e.g., why IA32_EFER.LMA and CPU mode are related to FRED here? "it's enough to " implies something else is not necessary. what is it? I don't think the original comment make them super clear. > >> Specifically, > >
