[PATCH 2/3] arm64: mm: Handle LVA support as a CPU feature
Ard Biesheuvel
ardb at kernel.org
Tue Nov 15 06:38:23 PST 2022
Currently, we detect CPU support for 52-bit virtual addressing (LVA)
extremely early, before creating the kernel page tables or enabling the
MMU. We cannot override the feature this early, and so large virtual
addressing is always enabled on CPUs that implement support for it if
the software support for it was enabled at build time. It also means we
rely on non-trivial code in asm to deal with this feature.
Given that both the ID map and the TTBR1 mapping of the kernel image are
guaranteed to be 48-bit addressable, it is not actually necessary to
enable support this early, and instead, we can model it as a CPU
feature. That way, we can rely on code patching to get the correct
TCR.T1SZ values programmed on secondary boot and suspend from resume.
On the primary boot path, we simply enable the MMU with 48-bit virtual
addressing initially, and update TCR.T1SZ from C code if LVA is
supported, right before creating the kernel mapping. Given that TTBR1
still points to reserved_pg_dir at this point, updating TCR.T1SZ should
be safe without the need for explicit TLB maintenance.
Since this gets rid of all accesses to the vabits_actual variable from
asm code that occurred before TCR.T1SZ had been programmed, we no longer
have a need for this variable, and we can replace it with a C expression
that produces the correct value directly, based on the value of TCR.T1SZ.
Signed-off-by: Ard Biesheuvel <ardb at kernel.org>
---
arch/arm64/include/asm/memory.h | 4 +++-
arch/arm64/kernel/cpufeature.c | 13 +++++++++++
arch/arm64/kernel/head.S | 24 +++-----------------
arch/arm64/kernel/pi/map_kernel.c | 12 ++++++++++
arch/arm64/kernel/sleep.S | 3 ---
arch/arm64/mm/mmu.c | 5 ----
arch/arm64/mm/proc.S | 16 ++++++-------
arch/arm64/tools/cpucaps | 1 +
8 files changed, 39 insertions(+), 39 deletions(-)
diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index a4e1d832a15a2d7a..20e15c3f4589bd38 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -183,9 +183,11 @@
#include <asm/boot.h>
#include <asm/bug.h>
#include <asm/sections.h>
+#include <asm/sysreg.h>
#if VA_BITS > 48
-extern u64 vabits_actual;
+// For reasons of #include hell, we can't use TCR_T1SZ_OFFSET/TCR_T1SZ_MASK here
+#define vabits_actual (64 - ((read_sysreg(tcr_el1) >> 16) & 63))
#else
#define vabits_actual ((u64)VA_BITS)
#endif
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index eca9df123a8b354b..b44aece5024c3e2d 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -2654,6 +2654,19 @@ static const struct arm64_cpu_capabilities arm64_features[] = {
.matches = has_cpuid_feature,
.cpu_enable = cpu_trap_el0_impdef,
},
+#ifdef CONFIG_ARM64_VA_BITS_52
+ {
+ .desc = "52-bit Virtual Addressing (LVA)",
+ .capability = ARM64_HAS_LVA,
+ .type = ARM64_CPUCAP_BOOT_CPU_FEATURE,
+ .sys_reg = SYS_ID_AA64MMFR2_EL1,
+ .sign = FTR_UNSIGNED,
+ .field_width = 4,
+ .field_pos = ID_AA64MMFR2_EL1_VARange_SHIFT,
+ .matches = has_cpuid_feature,
+ .min_field_value = ID_AA64MMFR2_EL1_VARange_52,
+ },
+#endif
{},
};
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 3b3c5e8e84af890e..6abf513189c7ebc9 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -80,7 +80,6 @@
* x20 primary_entry() .. __primary_switch() CPU boot mode
* x21 primary_entry() .. start_kernel() FDT pointer passed at boot in x0
* x22 create_idmap() .. start_kernel() ID map VA of the DT blob
- * x25 primary_entry() .. start_kernel() supported VA size
* x28 create_idmap() callee preserved temp register
*/
SYM_CODE_START(primary_entry)
@@ -95,14 +94,6 @@ SYM_CODE_START(primary_entry)
* On return, the CPU will be ready for the MMU to be turned on and
* the TCR will have been set.
*/
-#if VA_BITS > 48
- mrs_s x0, SYS_ID_AA64MMFR2_EL1
- tst x0, #0xf << ID_AA64MMFR2_EL1_VARange_SHIFT
- mov x0, #VA_BITS
- mov x25, #VA_BITS_MIN
- csel x25, x25, x0, eq
- mov x0, x25
-#endif
bl __cpu_setup // initialise processor
b __primary_switch
SYM_CODE_END(primary_entry)
@@ -406,11 +397,6 @@ SYM_FUNC_START_LOCAL(__primary_switched)
mov x0, x20
bl set_cpu_boot_mode_flag
-#if VA_BITS > 48
- adr_l x8, vabits_actual // Set this early so KASAN early init
- str x25, [x8] // ... observes the correct value
- dc civac, x8 // Make visible to booting secondaries
-#endif
#if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS)
bl kasan_early_init
#endif
@@ -525,9 +511,6 @@ SYM_FUNC_START_LOCAL(secondary_startup)
mov x20, x0 // preserve boot mode
bl finalise_el2
bl __cpu_secondary_check52bitva
-#if VA_BITS > 48
- ldr_l x0, vabits_actual
-#endif
bl __cpu_setup // initialise processor
adrp x1, swapper_pg_dir
adrp x2, idmap_pg_dir
@@ -628,10 +611,9 @@ SYM_FUNC_END(__enable_mmu)
SYM_FUNC_START(__cpu_secondary_check52bitva)
#if VA_BITS > 48
- ldr_l x0, vabits_actual
- cmp x0, #52
- b.ne 2f
-
+alternative_if_not ARM64_HAS_LVA
+ ret
+alternative_else_nop_endif
mrs_s x0, SYS_ID_AA64MMFR2_EL1
and x0, x0, #(0xf << ID_AA64MMFR2_EL1_VARange_SHIFT)
cbnz x0, 2f
diff --git a/arch/arm64/kernel/pi/map_kernel.c b/arch/arm64/kernel/pi/map_kernel.c
index 2bbf017147830bbe..3504e3266b02f636 100644
--- a/arch/arm64/kernel/pi/map_kernel.c
+++ b/arch/arm64/kernel/pi/map_kernel.c
@@ -122,6 +122,15 @@ static bool __init arm64_early_this_cpu_has_e0pd(void)
ID_AA64MMFR2_EL1_E0PD_SHIFT);
}
+static bool __init arm64_early_this_cpu_has_lva(void)
+{
+ u64 mmfr2;
+
+ mmfr2 = read_sysreg_s(SYS_ID_AA64MMFR2_EL1);
+ return cpuid_feature_extract_unsigned_field(mmfr2,
+ ID_AA64MMFR2_EL1_VARange_SHIFT);
+}
+
static bool __init arm64_early_this_cpu_has_pac(void)
{
u64 isar1, isar2;
@@ -274,6 +283,9 @@ asmlinkage void __init early_map_kernel(u64 boot_status, void *fdt)
/* Parse the command line for CPU feature overrides */
init_feature_override(boot_status, fdt, chosen);
+ if (VA_BITS > VA_BITS_MIN && arm64_early_this_cpu_has_lva())
+ sysreg_clear_set(tcr_el1, TCR_T1SZ_MASK, TCR_T1SZ(VA_BITS));
+
if (IS_ENABLED(CONFIG_ARM64_WXN) &&
cpuid_feature_extract_unsigned_field(arm64_sw_feature_override.val,
ARM64_SW_FEATURE_OVERRIDE_NOWXN))
diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
index 97c9de57725dfddb..617f78ad43a185c2 100644
--- a/arch/arm64/kernel/sleep.S
+++ b/arch/arm64/kernel/sleep.S
@@ -101,9 +101,6 @@ SYM_FUNC_END(__cpu_suspend_enter)
SYM_CODE_START(cpu_resume)
bl init_kernel_el
bl finalise_el2
-#if VA_BITS > 48
- ldr_l x0, vabits_actual
-#endif
bl __cpu_setup
/* enable the MMU early - so we can access sleep_save_stash by va */
adrp x1, swapper_pg_dir
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a9714b00f5410d7d..63fb62e16a1f8873 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -45,11 +45,6 @@
int idmap_t0sz __ro_after_init;
-#if VA_BITS > 48
-u64 vabits_actual __ro_after_init = VA_BITS_MIN;
-EXPORT_SYMBOL(vabits_actual);
-#endif
-
u64 kimage_voffset __ro_after_init;
EXPORT_SYMBOL(kimage_voffset);
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 98531775ff529dc8..02818fa6aded3218 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -400,8 +400,6 @@ SYM_FUNC_END(idmap_kpti_install_ng_mappings)
*
* Initialise the processor for turning the MMU on.
*
- * Input:
- * x0 - actual number of VA bits (ignored unless VA_BITS > 48)
* Output:
* Return in x0 the value of the SCTLR_EL1 register.
*/
@@ -426,20 +424,20 @@ 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 | \
+ mov_q tcr, TCR_TxSZ(VA_BITS_MIN) | 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
-#ifdef CONFIG_ARM64_VA_BITS_52
- sub x9, xzr, x0
- add x9, x9, #64
- tcr_set_t1sz tcr, x9
-#else
+#if VA_BITS > VA_BITS_MIN
+alternative_if ARM64_HAS_LVA
+ eor tcr, tcr, #TCR_T1SZ(VA_BITS) ^ TCR_T1SZ(VA_BITS_MIN)
+alternative_else_nop_endif
+#elif VA_BITS < 48
idmap_get_t0sz x9
-#endif
tcr_set_t0sz tcr, x9
+#endif
/*
* Set the IPS bits in TCR_EL1.
diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps
index f1c0347ec31a85c7..ec650a2cf4330179 100644
--- a/arch/arm64/tools/cpucaps
+++ b/arch/arm64/tools/cpucaps
@@ -30,6 +30,7 @@ HAS_GENERIC_AUTH_IMP_DEF
HAS_IRQ_PRIO_MASKING
HAS_LDAPR
HAS_LSE_ATOMICS
+HAS_LVA
HAS_NO_FPSIMD
HAS_NO_HW_PREFETCH
HAS_PAN
--
2.35.1
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