[PATCH v2 13/19] arm64: mm: add 5 level paging support to G-to-nG conversion routine

[Ard Biesheuvel]

Add support for 5 level paging in the G-to-nG routine that creates its
own temporary page tables to traverse the swapper page tables. Also add
support for running the 5 level configuration with the top level folded
at runtime, to support CPUs that do not implement the LPA2 extension.

While at it, wire up the level skipping logic so it will also trigger on
4 level configurations with LPA2 enabled at build time but not active at
runtime, as we'll fall back to 3 level paging in that case.

Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
 arch/arm64/kernel/cpufeature.c |  9 +++--
 arch/arm64/mm/proc.S           | 40 +++++++++++++++++++-
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 2ae42db621fe..c20c3cbd42ef 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1726,6 +1726,9 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
 	pgd_t *kpti_ng_temp_pgd;
 	u64 alloc = 0;
 
+	if (levels == 5 && !pgtable_l5_enabled())
+		levels = 4;
+
 	if (__this_cpu_read(this_cpu_vector) == vectors) {
 		const char *v = arm64_get_bp_hardening_vector(EL1_VECTOR_KPTI);
 
@@ -1753,9 +1756,9 @@ kpti_install_ng_mappings(const struct arm64_cpu_capabilities *__unused)
 		//
 		// The physical pages are laid out as follows:
 		//
-		// +--------+-/-------+-/------ +-\\--------+
-		// :  PTE[] : | PMD[] : | PUD[] : || PGD[]  :
-		// +--------+-\-------+-\------ +-//--------+
+		// +--------+-/-------+-/------ +-/------ +-\\\--------+
+		// :  PTE[] : | PMD[] : | PUD[] : | P4D[] : ||| PGD[]  :
+		// +--------+-\-------+-\------ +-\------ +-///--------+
 		//      ^
 		// The first page is mapped into this hierarchy at a PMD_SHIFT
 		// aligned virtual address, so that we can manipulate the PTE
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 6415623b7ebf..179e213bbe2d 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -282,6 +282,8 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 	end_ptep	.req	x15
 	pte		.req	x16
 	valid		.req	x17
+	cur_p4dp	.req	x19
+	end_p4dp	.req	x20
 
 	mov	x5, x3				// preserve temp_pte arg
 	mrs	swapper_ttb, ttbr1_el1
@@ -289,6 +291,12 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 
 	cbnz	cpu, __idmap_kpti_secondary
 
+#if CONFIG_PGTABLE_LEVELS > 4
+	stp	x29, x30, [sp, #-32]!
+	mov	x29, sp
+	stp	x19, x20, [sp, #16]
+#endif
+
 	/* We're the boot CPU. Wait for the others to catch up */
 	sevl
 1:	wfe
@@ -316,6 +324,14 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 	/* Everybody is enjoying the idmap, so we can rewrite swapper. */
 	/* PGD */
 	adrp		cur_pgdp, swapper_pg_dir
+#ifdef CONFIG_ARM64_LPA2
+alternative_if_not ARM64_HAS_LVA
+	/* skip one level of translation if 52-bit VAs are not enabled */
+	mov	pgd, cur_pgdp
+	add	end_pgdp, cur_pgdp, #8	// stop condition at pgd level
+	b	.Lderef_pgd
+alternative_else_nop_endif
+#endif
 	kpti_map_pgtbl	pgd, 0
 	kpti_mk_tbl_ng	pgd, PTRS_PER_PGD
 
@@ -329,16 +345,33 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 
 	/* Set the flag to zero to indicate that we're all done */
 	str	wzr, [flag_ptr]
+#if CONFIG_PGTABLE_LEVELS > 4
+	ldp	x19, x20, [sp, #16]
+	ldp	x29, x30, [sp], #32
+#endif
 	ret
 
 .Lderef_pgd:
+	/* P4D */
+	.if		CONFIG_PGTABLE_LEVELS > 4
+	p4d		.req	x30
+	pte_to_phys	cur_p4dp, pgd
+	kpti_map_pgtbl	p4d, 4
+	kpti_mk_tbl_ng	p4d, PTRS_PER_P4D
+	b		.Lnext_pgd
+	.else		/* CONFIG_PGTABLE_LEVELS <= 4 */
+	p4d		.req	pgd
+	.set		.Lnext_p4d, .Lnext_pgd
+	.endif
+
+.Lderef_p4d:
 	/* PUD */
 	.if		CONFIG_PGTABLE_LEVELS > 3
 	pud		.req	x10
-	pte_to_phys	cur_pudp, pgd
+	pte_to_phys	cur_pudp, p4d
 	kpti_map_pgtbl	pud, 1
 	kpti_mk_tbl_ng	pud, PTRS_PER_PUD
-	b		.Lnext_pgd
+	b		.Lnext_p4d
 	.else		/* CONFIG_PGTABLE_LEVELS <= 3 */
 	pud		.req	pgd
 	.set		.Lnext_pud, .Lnext_pgd
@@ -382,6 +415,9 @@ SYM_TYPED_FUNC_START(idmap_kpti_install_ng_mappings)
 	.unreq	end_ptep
 	.unreq	pte
 	.unreq	valid
+	.unreq	cur_p4dp
+	.unreq	end_p4dp
+	.unreq	p4d
 
 	/* Secondary CPUs end up here */
 __idmap_kpti_secondary:
-- 
2.38.1.584.g0f3c55d4c2-goog