x86/speculation: Add virtualized speculative store bypass disable support
Some AMD processors only support a non-architectural means of enabling speculative store bypass disable (SSBD). To allow a simplified view of this to a guest, an architectural definition has been created through a new CPUID bit, 0x80000008_EBX[25], and a new MSR, 0xc001011f. With this, a hypervisor can virtualize the existence of this definition and provide an architectural method for using SSBD to a guest. Add the new CPUID feature, the new MSR and update the existing SSBD support to use this MSR when present. Signed-off-by: NTom Lendacky <thomas.lendacky@amd.com> Signed-off-by: NThomas Gleixner <tglx@linutronix.de> Reviewed-by: NBorislav Petkov <bp@suse.de>
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