CSR_HENVCFG
nacl_csr_write(nsh, CSR_HENVCFG, cfg->henvcfg);
csr_write(CSR_HENVCFG, cfg->henvcfg);
prev = csr_read_clear(CSR_HENVCFG, ENVCFG_PMM);
csr_set(CSR_HENVCFG, value);
ret = (csr_read_clear(CSR_HENVCFG, ENVCFG_PMM) & ENVCFG_PMM) == value;
csr_write(CSR_HENVCFG, prev);
csr_write(CSR_HENVCFG, vcpu->arch.cfg.henvcfg);