Re: [PATCH v2 1/2] x86/cpu: Disable CR pinning during CPU bringup

[Dave Hansen]

On 3/9/26 06:46, Borislav Petkov wrote:
> My SNP guest stops booting with this right:

Could you dump out CR4 at wakeup_cpu_via_vmgexit() before and after this
patch? Right here:

        /* CR4 should maintain the MCE value */
        cr4 = native_read_cr4() & X86_CR4_MCE;

It's got to be some delta there.

The other possibility is that some CR4 bit becomes no longer pinned when
the CPU comes up, and the *pinning* was what caused the secondary CPU's
CR4 bit to get set, not its actual initialization.

Basically, the secondary boot code didn't explicitly set a bit and
counted on the pinning code to do it instead.

It's probably exacerbated by the "novel" way that SEV-SNP CPUs get
brought up and all the assembly that *only* runs there.