arm64: Move setting TCR_HD to C code

To allow for it to be more selective when we enable it, e.g. if the
CPU has an erratum that prevents us from doing so, move the check for
setting TCR_HD to C.

Reviewed by:	alc
Sponsored by:	Arm Ltd
Differential Revision:	https://reviews.freebsd.org/D47808

sys/arm64/arm64/locore.S

@@ -940,20 +940,17 @@ LENTRY(start_mmu)
 	bfi	x2, x3, #(TCR_ASID_SHIFT), #(TCR_ASID_WIDTH)
 
 	/*
-	 * Check if the HW supports access flag and dirty state updates,
-	 * and set TCR_EL1.HA and TCR_EL1.HD accordingly.
+	 * Check if the HW supports access flag updates, and set
+	 * TCR_EL1.HA accordingly. The TCR_EL1.HD flag to enable
+	 * HW management of dirty state is set in C code as it may
+	 * need to be disabled because of CPU errata.
 	 */
 	mrs	x3, id_aa64mmfr1_el1
 	and	x3, x3, #(ID_AA64MMFR1_HAFDBS_MASK)
-	cmp	x3, #1
-	b.ne	1f
-	orr 	x2, x2, #(TCR_HA)
-	b	2f
+	cbz	x3, 1f
+	orr	x2, x2, #(TCR_HA)
 1:
-	cmp	x3, #2
-	b.ne	2f
-	orr 	x2, x2, #(TCR_HA | TCR_HD)
-2:
+
 	msr	tcr_el1, x2
 
 	/*

sys/arm64/arm64/mp_machdep.c

@@ -219,6 +219,7 @@ init_secondary(uint64_t cpu)
 	pcpup = cpuid_to_pcpu[cpu];
 	pcpup->pc_midr = get_midr();
 	identify_cpu(cpu);
+	pmap_cpu_init();
 
 	/* Ensure the stores in identify_cpu have completed */
 	atomic_thread_fence_acq_rel();

sys/arm64/arm64/pmap.c

@@ -1309,6 +1309,8 @@ pmap_bootstrap(vm_size_t kernlen)
 	vm_paddr_t start_pa, pa;
 	uint64_t tcr;
 
+	pmap_cpu_init();
+
 	tcr = READ_SPECIALREG(tcr_el1);
 
 	/* Verify that the ASID is set through TTBR0. */
@@ -1623,6 +1625,25 @@ pmap_init_pv_table(void)
 	}
 }
 
+void
+pmap_cpu_init(void)
+{
+	uint64_t id_aa64mmfr1, tcr;
+
+	/* Enable HAFDBS if supported */
+	id_aa64mmfr1 = READ_SPECIALREG(id_aa64mmfr1_el1);
+	if (ID_AA64MMFR1_HAFDBS_VAL(id_aa64mmfr1) >=ID_AA64MMFR1_HAFDBS_AF_DBS){
+		tcr = READ_SPECIALREG(tcr_el1) | TCR_HD;
+		WRITE_SPECIALREG(tcr_el1, tcr);
+		isb();
+		/* Flush the local TLB for the TCR_HD flag change */
+		dsb(nshst);
+		__asm __volatile("tlbi vmalle1");
+		dsb(nsh);
+		isb();
+	}
+}
+
 /*
  *	Initialize the pmap module.
  *

sys/arm64/include/pmap.h

@@ -140,6 +140,7 @@ extern pt_entry_t pmap_sh_attr;
 
 void	pmap_activate_vm(pmap_t);
 void	pmap_bootstrap(vm_size_t);
+void	pmap_cpu_init(void);
 int	pmap_change_attr(vm_offset_t va, vm_size_t size, int mode);
 int	pmap_change_prot(vm_offset_t va, vm_size_t size, vm_prot_t prot);
 void	pmap_kenter(vm_offset_t sva, vm_size_t size, vm_paddr_t pa, int mode);