[PATCH v2 14/19] arm64: Enable LPA2 at boot if supported by the system

[Ard Biesheuvel <ardb@kernel.org>]

Update the early kernel mapping code to take 52-bit virtual addressing
into account based on the LPA2 feature. This is a bit more involved than
LVA (which is supported with 64k pages only), given that some page table
descriptor bits change meaning in this case.

To keep the handling in asm to a minimum, the initial ID map is still
created with 48-bit virtual addressing, which implies that the kernel
image must be loaded into 48-bit addressable physical memory. This is
currently required by the boot protocol, even though we happen to
support placement outside of that for LVA/64k based configurations.

Enabling LPA2 involves more than setting TCR.T1SZ to a lower value,
there is also a DS bit in TCR that needs to be set, and which changes
the meaning of bits [9:8] in all page table descriptors. Since we cannot
enable DS and every live page table descriptor at the same time, let's
pivot through another temporary mapping. This avoids the need to
reintroduce manipulations of the page tables with the MMU and caches
disabled.

To permit the LPA2 feature to be overridden on the kernel command line,
which may be necessary to work around silicon errata, or to deal with
mismatched features on heterogeneous SoC designs, test for CPU feature
overrides first, and only then enable LPA2.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 arch/arm64/include/asm/assembler.h      |   7 +-
 arch/arm64/include/asm/kernel-pgtable.h |  25 +++--
 arch/arm64/include/asm/memory.h         |   4 +
 arch/arm64/kernel/head.S                |   9 +-
 arch/arm64/kernel/image-vars.h          |   2 +
 arch/arm64/kernel/pi/map_kernel.c       | 103 +++++++++++++++++++-
 arch/arm64/mm/init.c                    |   2 +-
 arch/arm64/mm/mmu.c                     |   8 +-
 arch/arm64/mm/proc.S                    |   4 +
 9 files changed, 151 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
index 786bf62826a8..30eee6473cf0 100644
--- a/arch/arm64/include/asm/assembler.h
+++ b/arch/arm64/include/asm/assembler.h
@@ -609,11 +609,16 @@ alternative_endif
  * but we have to add an offset so that the TTBR1 address corresponds with the
  * pgdir entry that covers the lowest 48-bit addressable VA.
  *
+ * Note that this trick only works for LVA/64k pages - LPA2/4k pages uses an
+ * additional paging level, and on LPA2/16k pages, we would end up with a TTBR
+ * address that is not 64 byte aligned, so there we reduce the number of paging
+ * levels for the non-LPA2 case.
+ *
  * orr is used as it can cover the immediate value (and is idempotent).
  * 	ttbr: Value of ttbr to set, modified.
  */
 	.macro	offset_ttbr1, ttbr, tmp
-#ifdef CONFIG_ARM64_VA_BITS_52
+#if defined(CONFIG_ARM64_VA_BITS_52) && !defined(CONFIG_ARM64_LPA2)
 	mrs	\tmp, tcr_el1
 	and	\tmp, \tmp, #TCR_T1SZ_MASK
 	cmp	\tmp, #TCR_T1SZ(VA_BITS_MIN)
diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index faa11e8b4a0e..2359b2af0c4c 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -20,12 +20,16 @@
  */
 #ifdef CONFIG_ARM64_4K_PAGES
 #define INIT_IDMAP_USES_PMD_MAPS	1
-#define INIT_IDMAP_TABLE_LEVELS		(CONFIG_PGTABLE_LEVELS - 1)
 #else
 #define INIT_IDMAP_USES_PMD_MAPS	0
-#define INIT_IDMAP_TABLE_LEVELS		(CONFIG_PGTABLE_LEVELS)
 #endif
 
+/* how many levels of translation are required to cover 'x' bits of VA space */
+#define VA_LEVELS(x)		(((x) - 4) / (PAGE_SHIFT - 3))
+#define INIT_IDMAP_TABLE_LEVELS	(VA_LEVELS(VA_BITS_MIN) - INIT_IDMAP_USES_PMD_MAPS)
+
+#define INIT_IDMAP_ROOT_SHIFT	(VA_LEVELS(VA_BITS_MIN) * (PAGE_SHIFT - 3) + 3)
+
 /*
  * If KASLR is enabled, then an offset K is added to the kernel address
  * space. The bottom 21 bits of this offset are zero to guarantee 2MB
@@ -52,7 +56,14 @@
 #define EARLY_ENTRIES(vstart, vend, shift, add) \
 	((((vend) - 1) >> (shift)) - ((vstart) >> (shift)) + 1 + add)
 
-#define EARLY_PGDS(vstart, vend, add) (EARLY_ENTRIES(vstart, vend, PGDIR_SHIFT, add))
+#if CONFIG_PGTABLE_LEVELS > 4
+/* the kernel is covered entirely by the pgd_t at the top of the VA space */
+#define EARLY_PGDS	1
+#else
+#define EARLY_PGDS	0
+#endif
+
+#define EARLY_P4DS(vstart, vend, add) (EARLY_ENTRIES(vstart, vend, INIT_IDMAP_ROOT_SHIFT, add))
 
 #if INIT_IDMAP_TABLE_LEVELS > 3
 #define EARLY_PUDS(vstart, vend, add) (EARLY_ENTRIES(vstart, vend, PUD_SHIFT, add))
@@ -66,11 +77,13 @@
 #define EARLY_PMDS(vstart, vend, add) (0)
 #endif
 
-#define EARLY_PAGES(vstart, vend, add) ( 1 			/* PGDIR page */				\
-			+ EARLY_PGDS((vstart), (vend), add) 	/* each PGDIR needs a next level page table */	\
+#define EARLY_PAGES(vstart, vend, add) ( 1 			/* PGDIR/P4D page */				\
+			+ EARLY_P4DS((vstart), (vend), add) 	/* each P4D needs a next level page table */	\
 			+ EARLY_PUDS((vstart), (vend), add)	/* each PUD needs a next level page table */	\
 			+ EARLY_PMDS((vstart), (vend), add))	/* each PMD needs a next level page table */
-#define INIT_DIR_SIZE (PAGE_SIZE * (EARLY_PAGES(KIMAGE_VADDR, _end, EARLY_KASLR) + EARLY_SEGMENT_EXTRA_PAGES))
+
+#define INIT_DIR_SIZE	(PAGE_SIZE * (EARLY_PAGES(KIMAGE_VADDR, _end, EARLY_KASLR) + \
+			 EARLY_SEGMENT_EXTRA_PAGES + EARLY_PGDS))
 
 /* the initial ID map may need two extra pages if it needs to be extended */
 #if VA_BITS_MIN < 48
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index b3826ff2e52b..4f617e271008 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -54,7 +54,11 @@
 #define FIXADDR_TOP		(VMEMMAP_START - SZ_32M)
 
 #if VA_BITS > 48
+#ifdef CONFIG_ARM64_16K_PAGES
+#define VA_BITS_MIN		(47)
+#else
 #define VA_BITS_MIN		(48)
+#endif
 #else
 #define VA_BITS_MIN		(VA_BITS)
 #endif
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 94de42dfe97d..6be121949c06 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -198,7 +198,7 @@ SYM_CODE_END(preserve_boot_args)
 	mov \tbl, \sv
 	.endif
 .L_\@:
-	compute_indices \vstart, \vend, #PGDIR_SHIFT, \istart, \iend, \count
+	compute_indices \vstart, \vend, #INIT_IDMAP_ROOT_SHIFT, \istart, \iend, \count
 	mov \sv, \rtbl
 	populate_entries \tbl, \rtbl, \istart, \iend, #PMD_TYPE_TABLE, #PAGE_SIZE, \tmp
 	mov \tbl, \sv
@@ -610,9 +610,16 @@ SYM_FUNC_START(__cpu_secondary_check52bitva)
 alternative_if_not ARM64_HAS_LVA
 	ret
 alternative_else_nop_endif
+#ifndef CONFIG_ARM64_LPA2
 	mrs_s	x0, SYS_ID_AA64MMFR2_EL1
 	and	x0, x0, #(0xf << ID_AA64MMFR2_EL1_VARange_SHIFT)
 	cbnz	x0, 2f
+#else
+	mrs	x0, id_aa64mmfr0_el1
+	sbfx	x0, x0, #ID_AA64MMFR0_EL1_TGRAN_SHIFT, 4
+	cmp	x0, #ID_AA64MMFR0_EL1_TGRAN_LPA2
+	b.ge	2f
+#endif
 
 	update_early_cpu_boot_status \
 		CPU_STUCK_IN_KERNEL | CPU_STUCK_REASON_52_BIT_VA, x0, x1
diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index 82bafa1f869c..f48b6f09d278 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -56,6 +56,8 @@ PROVIDE(__pi_arm64_sw_feature_override	= arm64_sw_feature_override);
 PROVIDE(__pi_arm64_use_ng_mappings	= arm64_use_ng_mappings);
 PROVIDE(__pi__ctype			= _ctype);
 
+PROVIDE(__pi_init_idmap_pg_dir		= init_idmap_pg_dir);
+PROVIDE(__pi_init_idmap_pg_end		= init_idmap_pg_end);
 PROVIDE(__pi_init_pg_dir		= init_pg_dir);
 PROVIDE(__pi_init_pg_end		= init_pg_end);
 PROVIDE(__pi_swapper_pg_dir		= swapper_pg_dir);
diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
index a9472ab8d901..75d643da56c8 100644
--- a/arch/arm64/kernel/pi/map_kernel.c
+++ b/arch/arm64/kernel/pi/map_kernel.c
@@ -133,6 +133,20 @@ static bool __init arm64_early_this_cpu_has_lva(void)
 						    ID_AA64MMFR2_EL1_VARange_SHIFT);
 }
 
+static bool __init arm64_early_this_cpu_has_lpa2(void)
+{
+	u64 mmfr0;
+	int feat;
+
+	mmfr0 = read_sysreg(id_aa64mmfr0_el1);
+	mmfr0 &= ~id_aa64mmfr0_override.mask;
+	mmfr0 |= id_aa64mmfr0_override.val;
+	feat = cpuid_feature_extract_signed_field(mmfr0,
+						  ID_AA64MMFR0_EL1_TGRAN_SHIFT);
+
+	return feat >= ID_AA64MMFR0_EL1_TGRAN_LPA2;
+}
+
 static bool __init arm64_early_this_cpu_has_pac(void)
 {
 	u64 isar1, isar2;
@@ -254,11 +268,85 @@ static void __init map_kernel(u64 kaslr_offset, u64 va_offset, int root_level)
 	}
 
 	/* Copy the root page table to its final location */
-	memcpy((void *)swapper_pg_dir + va_offset, init_pg_dir, PGD_SIZE);
+	memcpy((void *)swapper_pg_dir + va_offset, init_pg_dir, PAGE_SIZE);
 	dsb(ishst);
 	idmap_cpu_replace_ttbr1(swapper_pg_dir);
 }
 
+static void noinline __section(".idmap.text") set_ttbr0_for_lpa2(u64 ttbr)
+{
+	u64 sctlr = read_sysreg(sctlr_el1);
+	u64 tcr = read_sysreg(tcr_el1) | TCR_DS;
+
+	/* Update TCR.T0SZ in case we entered with a 47-bit ID map */
+	tcr &= ~TCR_T0SZ_MASK;
+	tcr |= TCR_T0SZ(48);
+
+	asm("	msr	sctlr_el1, %0		;"
+	    "	isb				;"
+	    "   msr     ttbr0_el1, %1		;"
+	    "   msr     tcr_el1, %2		;"
+	    "	isb				;"
+	    "	tlbi    vmalle1			;"
+	    "	dsb     nsh			;"
+	    "	isb				;"
+	    "	msr     sctlr_el1, %3		;"
+	    "	isb				;"
+	    ::	"r"(sctlr & ~SCTLR_ELx_M), "r"(ttbr), "r"(tcr), "r"(sctlr));
+}
+
+static void remap_idmap_for_lpa2(void)
+{
+	extern pgd_t init_idmap_pg_dir[], init_idmap_pg_end[];
+	pgd_t *pgdp = (void *)init_pg_dir + PAGE_SIZE;
+	pgprot_t text_prot = PAGE_KERNEL_ROX;
+	pgprot_t data_prot = PAGE_KERNEL;
+
+	/* clear the bits that change meaning once LPA2 is turned on */
+	pgprot_val(text_prot) &= ~PTE_SHARED;
+	pgprot_val(data_prot) &= ~PTE_SHARED;
+
+	/*
+	 * We have to clear bits [9:8] in all block or page descriptors in the
+	 * initial ID map, as otherwise they will be (mis)interpreted as
+	 * physical address bits once we flick the LPA2 switch (TCR.DS). Since
+	 * we cannot manipulate live descriptors in that way without creating
+	 * potential TLB conflicts, let's create another temporary ID map in a
+	 * LPA2 compatible fashion, and update the initial ID map while running
+	 * from that.
+	 */
+	map_segment(init_pg_dir, &pgdp, 0, _stext, __inittext_end, text_prot,
+		    false, 0);
+	map_segment(init_pg_dir, &pgdp, 0, __initdata_begin, _end, data_prot,
+		    false, 0);
+	dsb(ishst);
+	set_ttbr0_for_lpa2((u64)init_pg_dir);
+
+	/*
+	 * Recreate the initial ID map with the same granularity as before.
+	 * Don't bother with the FDT, we no longer need it after this.
+	 */
+	memset(init_idmap_pg_dir, 0,
+	       (u64)init_idmap_pg_dir - (u64)init_idmap_pg_end);
+
+	pgdp = (void *)init_idmap_pg_dir + PAGE_SIZE;
+	map_segment(init_idmap_pg_dir, &pgdp, 0,
+		    PTR_ALIGN_DOWN(&_stext[0], INIT_IDMAP_BLOCK_SIZE),
+		    PTR_ALIGN_DOWN(&__bss_start[0], INIT_IDMAP_BLOCK_SIZE),
+		    text_prot, false, 0);
+	map_segment(init_idmap_pg_dir, &pgdp, 0,
+		    PTR_ALIGN_DOWN(&__bss_start[0], INIT_IDMAP_BLOCK_SIZE),
+		    PTR_ALIGN(&_end[0], INIT_IDMAP_BLOCK_SIZE),
+		    data_prot, false, 0);
+	dsb(ishst);
+
+	/* switch back to the updated initial ID map */
+	set_ttbr0_for_lpa2((u64)init_idmap_pg_dir);
+
+	/* wipe the temporary ID map from memory */
+	memset(init_pg_dir, 0, (u64)init_pg_end - (u64)init_pg_dir);
+}
+
 asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
 {
 	static char const chosen_str[] __initconst = "/chosen";
@@ -266,6 +354,7 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
 	u64 va_base, pa_base = (u64)&_text;
 	u64 kaslr_offset = pa_base % MIN_KIMG_ALIGN;
 	int root_level = 4 - CONFIG_PGTABLE_LEVELS;
+	bool va52 = (VA_BITS == 52);
 
 	/* Clear BSS and the initial page tables */
 	memset(__bss_start, 0, (u64)init_pg_end - (u64)__bss_start);
@@ -295,7 +384,17 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
 			arm64_use_ng_mappings = true;
 	}
 
-	if (VA_BITS == 52 && arm64_early_this_cpu_has_lva())
+	if (IS_ENABLED(CONFIG_ARM64_LPA2)) {
+		if (arm64_early_this_cpu_has_lpa2()) {
+			remap_idmap_for_lpa2();
+		} else {
+			va52 = false;
+			root_level++;
+		}
+	} else if (IS_ENABLED(CONFIG_ARM64_64K_PAGES)) {
+		va52 &= arm64_early_this_cpu_has_lva();
+	}
+	if (va52)
 		sysreg_clear_set(tcr_el1, TCR_T1SZ_MASK, TCR_T1SZ(VA_BITS));
 
 	va_base = KIMAGE_VADDR + kaslr_offset;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 4b4651ee47f2..498d327341b4 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -315,7 +315,7 @@ void __init arm64_memblock_init(void)
 	 * physical address of PAGE_OFFSET, we have to *subtract* from it.
 	 */
 	if (IS_ENABLED(CONFIG_ARM64_VA_BITS_52) && (vabits_actual != 52))
-		memstart_addr -= _PAGE_OFFSET(48) - _PAGE_OFFSET(52);
+		memstart_addr -= _PAGE_OFFSET(vabits_actual) - _PAGE_OFFSET(52);
 
 	/*
 	 * Apply the memory limit if it was set. Since the kernel may be loaded
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index d089bc78e592..ba5423ff7039 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -541,8 +541,12 @@ static void __init map_mem(pgd_t *pgdp)
 	 * entries at any level are being shared between the linear region and
 	 * the vmalloc region. Check whether this is true for the PGD level, in
 	 * which case it is guaranteed to be true for all other levels as well.
+	 * (Unless we are running with support for LPA2, in which case the
+	 * entire reduced VA space is covered by a single pgd_t which will have
+	 * been populated without the PXNTable attribute by the time we get here.)
 	 */
-	BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end));
+	BUILD_BUG_ON(pgd_index(direct_map_end - 1) == pgd_index(direct_map_end) &&
+		     pgd_index(_PAGE_OFFSET(VA_BITS_MIN)) != PTRS_PER_PGD - 1);
 
 	if (can_set_direct_map())
 		flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
@@ -726,7 +730,7 @@ static void __init create_idmap(void)
 
 void __init paging_init(void)
 {
-	idmap_t0sz = 63UL - __fls(__pa_symbol(_end) | GENMASK(VA_BITS_MIN - 1, 0));
+	idmap_t0sz = 63UL - __fls(__pa_symbol(_end) | GENMASK(vabits_actual - 1, 0));
 
 	map_mem(swapper_pg_dir);
 
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 179e213bbe2d..d95df732b672 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -489,7 +489,11 @@ SYM_FUNC_START(__cpu_setup)
 #if VA_BITS > VA_BITS_MIN
 	mov		x9, #64 - VA_BITS
 alternative_if ARM64_HAS_LVA
+	tcr_set_t0sz	tcr, x9
 	tcr_set_t1sz	tcr, x9
+#ifdef CONFIG_ARM64_LPA2
+	orr		tcr, tcr, #TCR_DS
+#endif
 alternative_else_nop_endif
 #endif
 
-- 
2.38.1.584.g0f3c55d4c2-goog


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