[PATCH v3 35/60] arm64: mm: Use 48-bit virtual addressing for the permanent ID map

Ard Biesheuvel
2023-03-07T14:12:25Z

Even though we support loading kernels anywhere in 48-bit addressable
physical memory, we create the ID maps based on the number of levels
that we happened to configure for the kernel VA and user VA spaces.

The reason for this is that the PGD/PUD/PMD based classification of
translation levels, along with the associated folding when the number of
levels is less than 5, does not permit creating a page table hierarchy
of a set number of levels. This means that, for instance, on 39-bit VA
kernels we need to configure an additional level above PGD level on the
fly, and 36-bit VA kernels still only support 47-bit virtual addressing
with this trick applied.

Now that we have a separate helper to populate page table hierarchies
that does not define the levels in terms of PUDS/PMDS/etc at all, let's
reuse it to create the permanent ID map with a fixed VA size of 48 bits.

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
arch/arm64/include/asm/kernel-pgtable.h | 2 ++
arch/arm64/kernel/head.S | 5 +++
arch/arm64/kvm/mmu.c | 15 +++------
arch/arm64/mm/mmu.c | 32 +++++++++++---------
arch/arm64/mm/proc.S | 9 ++----
5 files changed, 31 insertions(+), 32 deletions(-)

diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
index 50b5c145358a5d8e..2a2c80ffe59e5307 100644
--- a/arch/arm64/include/asm/kernel-pgtable.h
+++ b/arch/arm64/include/asm/kernel-pgtable.h
@@ -35,6 +35,8 @@
#define SWAPPER_PGTABLE_LEVELS (CONFIG_PGTABLE_LEVELS)
#endif

+#define IDMAP_LEVELS ARM64_HW_PGTABLE_LEVELS(48)
+#define IDMAP_ROOT_LEVEL (4 - IDMAP_LEVELS)

/*
* If KASLR is enabled, then an offset K is added to the kernel address
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index e45fd99e8ab4272a..fc6a4076d826b728 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -727,6 +727,11 @@ SYM_FUNC_START_LOCAL(__no_granule_support)
SYM_FUNC_END(__no_granule_support)

SYM_FUNC_START_LOCAL(__primary_switch)
+ mrs x1, tcr_el1
+ mov x2, #64 - VA_BITS
+ tcr_set_t0sz x1, x2
+ msr tcr_el1, x1
+
adrp x1, reserved_pg_dir
adrp x2, init_idmap_pg_dir
bl __enable_mmu
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 7113587222ffe8e1..d64be7b5f6692e8b 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1687,16 +1687,9 @@ int __init kvm_mmu_init(u32 *hyp_va_bits)
BUG_ON((hyp_idmap_start ^ (hyp_idmap_end - 1)) & PAGE_MASK);

/*
- * The ID map may be configured to use an extended virtual address
- * range. This is only the case if system RAM is out of range for the
- * currently configured page size and VA_BITS_MIN, in which case we will
- * also need the extended virtual range for the HYP ID map, or we won't
- * be able to enable the EL2 MMU.
- *
- * However, in some cases the ID map may be configured for fewer than
- * the number of VA bits used by the regular kernel stage 1. This
- * happens when VA_BITS=52 and the kernel image is placed in PA space
- * below 48 bits.
+ * The ID map is always configured for 48 bits of translation, which
+ * may be fewer than the number of VA bits used by the regular kernel
+ * stage 1, when VA_BITS=52.
*
* At EL2, there is only one TTBR register, and we can't switch between
* translation tables *and* update TCR_EL2.T0SZ at the same time. Bottom
@@ -1707,7 +1700,7 @@ int __init kvm_mmu_init(u32 *hyp_va_bits)
* 1 VA bits to assure that the hypervisor can both ID map its code page
* and map any kernel memory.
*/
- idmap_bits = 64 - ((idmap_t0sz & TCR_T0SZ_MASK) >> TCR_T0SZ_OFFSET);
+ idmap_bits = 48;
kernel_bits = vabits_actual;
*hyp_va_bits = max(idmap_bits, kernel_bits);

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 81e1420d2cc13246..a59433ae4f5f8d02 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -762,22 +762,21 @@ static void __init map_kernel(pgd_t *pgdp)
kasan_copy_shadow(pgdp);
}

+void __pi_map_range(u64 *pgd, u64 start, u64 end, u64 pa, pgprot_t prot,
+ int level, pte_t *tbl, bool may_use_cont, u64 va_offset);
+
+static u8 idmap_ptes[IDMAP_LEVELS - 1][PAGE_SIZE] __aligned(PAGE_SIZE) __ro_after_init,
+ kpti_ptes[IDMAP_LEVELS - 1][PAGE_SIZE] __aligned(PAGE_SIZE) __ro_after_init;
+
static void __init create_idmap(void)
{
u64 start = __pa_symbol(__idmap_text_start);
- u64 size = __pa_symbol(__idmap_text_end) - start;
- pgd_t *pgd = idmap_pg_dir;
- u64 pgd_phys;
-
- /* check if we need an additional level of translation */
- if (VA_BITS < 48 && idmap_t0sz < (64 - VA_BITS_MIN)) {
- pgd_phys = early_pgtable_alloc(PAGE_SHIFT);
- set_pgd(&idmap_pg_dir[start >> VA_BITS],
- __pgd(pgd_phys | P4D_TYPE_TABLE));
- pgd = __va(pgd_phys);
- }
- __create_pgd_mapping(pgd, start, start, size, PAGE_KERNEL_ROX,
- early_pgtable_alloc, 0);
+ u64 end = __pa_symbol(__idmap_text_end);
+ u64 ptep = __pa_symbol(idmap_ptes);
+
+ __pi_map_range(&ptep, start, end, start, PAGE_KERNEL_ROX,
+ IDMAP_ROOT_LEVEL, (pte_t *)idmap_pg_dir, false,
+ __phys_to_virt(ptep) - ptep);

if (IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) {
extern u32 __idmap_kpti_flag;
@@ -787,8 +786,10 @@ static void __init create_idmap(void)
* The KPTI G-to-nG conversion code needs a read-write mapping
* of its synchronization flag in the ID map.
*/
- __create_pgd_mapping(pgd, pa, pa, sizeof(u32), PAGE_KERNEL,
- early_pgtable_alloc, 0);
+ ptep = __pa_symbol(kpti_ptes);
+ __pi_map_range(&ptep, pa, pa + sizeof(u32), pa, PAGE_KERNEL,
+ IDMAP_ROOT_LEVEL, (pte_t *)idmap_pg_dir, false,
+ __phys_to_virt(ptep) - ptep);
}
}

@@ -813,6 +814,7 @@ void __init paging_init(void)
memblock_allow_resize();

create_idmap();
+ idmap_t0sz = TCR_T0SZ(48);
}

#ifdef CONFIG_MEMORY_HOTPLUG
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 82e88f4521737c0e..c7129b21bfd5191f 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -422,9 +422,9 @@ SYM_FUNC_START(__cpu_setup)
mair .req x17
tcr .req x16
mov_q mair, MAIR_EL1_SET
- mov_q tcr, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
- TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
- TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS | TCR_MTE_FLAGS
+ mov_q tcr, TCR_T0SZ(48) | TCR_T1SZ(VA_BITS) | TCR_CACHE_FLAGS | \
+ TCR_SMP_FLAGS | TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
+ TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS | TCR_MTE_FLAGS

tcr_clear_errata_bits tcr, x9, x5

@@ -432,10 +432,7 @@ SYM_FUNC_START(__cpu_setup)
sub x9, xzr, x0
add x9, x9, #64
tcr_set_t1sz tcr, x9
-#else
- idmap_get_t0sz x9
#endif
- tcr_set_t0sz tcr, x9

/*
* Set the IPS bits in TCR_EL1.
--
2.39.2