Sporadic realm linux boot failure about islet HOT 2 CLOSED

// realm-linux kernel code
void *__init fixmap_remap_fdt(phys_addr_t dt_phys, int *size, pgprot_t prot)
{
    // in error cases, dt_phys (the address of FDT) is zero, so this function returns NULL.
    if (!dt_phys || dt_phys % MIN_FDT_ALIGN)
        return NULL;
}

// islet rmm log (I added for debugging)
[JB] vcpu x0: 0x0, x1: 0xA, elr: 0x80000000  --> when we try to jump to Realm's kernel start, x0 contains "zero" for some reason.

// (1) nw-linux kernel code
// host creates a page (not initialized page by zero) for rec, and give ISLET RMM the physical address of the page.
rec->rec_page = (void *)__get_free_page(GFP_KERNEL);    

// (2) Rec initialization in ISLET RMM
// The below new() function is used to initialize the rec page that the host provided.
// But, we by accident do not initialize "Rec.ripas".
// Even worse, the rec page is not initialized by the host kernel as well.
// So, "Rec.ripas" may contain an unexpected value. In most cases, it will be "zero", but sometimes it may be not "zero".
This is the reason why this bug is triggered sporadically.
pub struct Rec {
    pub rd: &'static Rd,
    vcpuid: usize,
    ripas: Ripas,
}
pub unsafe fn new(
        rec_addr: usize,
        vcpuid: usize,
        rd: &'static Rd,
    ) -> ManuallyDrop<&'static mut Rec> {
        let rec: &mut Rec = &mut *(rec_addr as *mut Rec);
        rec.vcpuid = vcpuid;
        rec.rd = rd;
        ManuallyDrop::new(rec)
    }

listen!(mainloop, rmi::REC_ENTER, |arg, ret, rmm| {
    ....
    let ripas = rec.ripas_addr();   // (1) we try to read "Rec.ripas" that is uninitialized variable.
     if ripas > 0 {   // (2) if the uninitialized variable happens to be a larger than 0,
         rmi.set_reg(rec.rd.id(), rec.id(), 0, 0)?;   // (3) we set "zero" to "x0" register for the vcpu.
         rmi.set_reg(rec.rd.id(), rec.id(), 1, ripas)?;
         rec.set_ripas(0, 0, 0, 0);
      }
    ....
     // (4) when we run a realm with the above vcpu context, it faces the mentioned FDT error!
     match rmi.run(rec.rd.id(), rec.id(), 0) {
}

pub unsafe fn new(
        rec_addr: usize,
        vcpuid: usize,
        rd: &'static Rd,
    ) -> ManuallyDrop<&'static mut Rec> {
        let rec: &mut Rec = &mut *(rec_addr as *mut Rec);
        rec.vcpuid = vcpuid;
        rec.rd = rd;
        rec.set_ripas(0, 0, 0, 0);   // This is a fix!
        ManuallyDrop::new(rec)
    }