[PATCH v3] arm64: mm: increase VA range of identity map
Ard Biesheuvel
ard.biesheuvel at linaro.org
Thu Feb 26 01:16:55 PST 2015
The page size and the number of translation levels, and hence the supported
virtual address range, are build-time configurables on arm64 whose optimal
values are use case dependent. However, in the current implementation, if
the system's RAM is located at a very high offset, the virtual address range
needs to reflect that merely because the identity mapping, which is only used
to enable or disable the MMU, requires the extended virtual range to map the
physical memory at an equal virtual offset.
This patch relaxes that requirement, by increasing the number of translation
levels for the identity mapping only, and only when actually needed, i.e.,
when system RAM's offset is found to be out of reach at runtime.
Tested-by: Laura Abbott <lauraa at codeaurora.org>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
---
v3:
- Fix potential issue where the assumption would not hold that lowering T0SZ
would always result in an additional level of translation to be configured.
- Use EXTRA_PTRS not PTRS_PER_PGD: doesn't really make a difference in practice,
but it looks more correct.
- Increased verbosity of the comments
- Dropped # prefixes for immediates in asm, per Will's request
- Retained Laura's Tested-by tag since the emitted code is identical
v2:
- Dropped hunk regarding KVM, this will be addressed separately. Note that the
build is still broken on Seattle if you have KVM enabled and 4k pages with
3 levels of translation configured, but at least you have something to watch
on your console now
- Fix ordering wrt TLB flushing
- Set T0SZ based on actual leading zero count in __pa(KERNEL_END), the net
result is the same (one additional level of translation, if needed)
arch/arm64/include/asm/mmu_context.h | 38 ++++++++++++++++++++++++++++++++++
arch/arm64/include/asm/page.h | 6 ++++--
arch/arm64/include/asm/pgtable-hwdef.h | 7 ++++++-
arch/arm64/kernel/head.S | 38 ++++++++++++++++++++++++++++++++++
arch/arm64/kernel/smp.c | 1 +
arch/arm64/mm/mmu.c | 7 ++++++-
arch/arm64/mm/proc-macros.S | 11 ++++++++++
arch/arm64/mm/proc.S | 3 +++
8 files changed, 107 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/include/asm/mmu_context.h b/arch/arm64/include/asm/mmu_context.h
index a9eee33dfa62..9dea19aae40c 100644
--- a/arch/arm64/include/asm/mmu_context.h
+++ b/arch/arm64/include/asm/mmu_context.h
@@ -64,6 +64,44 @@ static inline void cpu_set_reserved_ttbr0(void)
: "r" (ttbr));
}
+/*
+ * TCR.T0SZ value to use when the ID map is active. Usually equals
+ * TCR_T0SZ(VA_BITS), unless system RAM is positioned very high in
+ * physical memory, in which case it will be smaller.
+ */
+extern u64 idmap_t0sz;
+
+static inline void __cpu_set_tcr_t0sz(u64 t0sz)
+{
+ unsigned long tcr;
+
+ if (!IS_ENABLED(CONFIG_ARM64_VA_BITS_48)
+ && unlikely(idmap_t0sz != TCR_T0SZ(VA_BITS)))
+ asm volatile (
+ " mrs %0, tcr_el1 ;"
+ " bfi %0, %1, %2, %3 ;"
+ " msr tcr_el1, %0 ;"
+ " isb"
+ : "=&r" (tcr)
+ : "r"(t0sz), "I"(TCR_T0SZ_OFFSET), "I"(TCR_TxSZ_WIDTH));
+}
+
+/*
+ * Set TCR.T0SZ to the value appropriate for activating the identity map.
+ */
+static inline void cpu_set_idmap_tcr_t0sz(void)
+{
+ __cpu_set_tcr_t0sz(idmap_t0sz);
+}
+
+/*
+ * Set TCR.T0SZ to its default value (based on VA_BITS)
+ */
+static inline void cpu_set_default_tcr_t0sz(void)
+{
+ __cpu_set_tcr_t0sz(TCR_T0SZ(VA_BITS));
+}
+
static inline void switch_new_context(struct mm_struct *mm)
{
unsigned long flags;
diff --git a/arch/arm64/include/asm/page.h b/arch/arm64/include/asm/page.h
index 22b16232bd60..3d02b1869eb8 100644
--- a/arch/arm64/include/asm/page.h
+++ b/arch/arm64/include/asm/page.h
@@ -33,7 +33,9 @@
* image. Both require pgd, pud (4 levels only) and pmd tables to (section)
* map the kernel. With the 64K page configuration, swapper and idmap need to
* map to pte level. The swapper also maps the FDT (see __create_page_tables
- * for more information).
+ * for more information). Note that the number of ID map translation levels
+ * could be increased on the fly if system RAM is out of reach for the default
+ * VA range, so 3 pages are reserved in all cases.
*/
#ifdef CONFIG_ARM64_64K_PAGES
#define SWAPPER_PGTABLE_LEVELS (CONFIG_ARM64_PGTABLE_LEVELS)
@@ -42,7 +44,7 @@
#endif
#define SWAPPER_DIR_SIZE (SWAPPER_PGTABLE_LEVELS * PAGE_SIZE)
-#define IDMAP_DIR_SIZE (SWAPPER_DIR_SIZE)
+#define IDMAP_DIR_SIZE (3 * PAGE_SIZE)
#ifndef __ASSEMBLY__
diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
index 5f930cc9ea83..847e864202cc 100644
--- a/arch/arm64/include/asm/pgtable-hwdef.h
+++ b/arch/arm64/include/asm/pgtable-hwdef.h
@@ -143,7 +143,12 @@
/*
* TCR flags.
*/
-#define TCR_TxSZ(x) (((UL(64) - (x)) << 16) | ((UL(64) - (x)) << 0))
+#define TCR_T0SZ_OFFSET 0
+#define TCR_T1SZ_OFFSET 16
+#define TCR_T0SZ(x) ((UL(64) - (x)) << TCR_T0SZ_OFFSET)
+#define TCR_T1SZ(x) ((UL(64) - (x)) << TCR_T1SZ_OFFSET)
+#define TCR_TxSZ(x) (TCR_T0SZ(x) | TCR_T1SZ(x))
+#define TCR_TxSZ_WIDTH 6
#define TCR_IRGN_NC ((UL(0) << 8) | (UL(0) << 24))
#define TCR_IRGN_WBWA ((UL(1) << 8) | (UL(1) << 24))
#define TCR_IRGN_WT ((UL(2) << 8) | (UL(2) << 24))
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 8ce88e08c030..a3612eadab3c 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -387,6 +387,44 @@ __create_page_tables:
mov x0, x25 // idmap_pg_dir
ldr x3, =KERNEL_START
add x3, x3, x28 // __pa(KERNEL_START)
+
+#ifndef CONFIG_ARM64_VA_BITS_48
+#define EXTRA_SHIFT (PGDIR_SHIFT + PAGE_SHIFT - 3)
+#define EXTRA_PTRS (1 << (48 - EXTRA_SHIFT))
+
+ /*
+ * If VA_BITS < 48, it may be too small to allow for an ID mapping to be
+ * created that covers system RAM if that is located sufficiently high
+ * in the physical address space. So for the ID map, use an extended
+ * virtual range in that case, by configuring an additional translation
+ * level.
+ * First, we have to verify our assumption that the current value of
+ * VA_BITS was chosen such that all translation levels are fully
+ * utilised, and that lowering T0SZ will always result in an additional
+ * translation level to be configured.
+ */
+#if VA_BITS != EXTRA_SHIFT
+#error "Mismatch between VA_BITS and page size/number of translation levels"
+#endif
+
+ /*
+ * Calculate the maximum allowed value for TCR_EL1.T0SZ so that the
+ * entire kernel image can be ID mapped. As T0SZ == (64 - #bits used),
+ * this number conveniently equals the number of leading zeroes in
+ * the physical address of KERNEL_END.
+ */
+ adrp x5, KERNEL_END
+ clz x5, x5
+ cmp x5, TCR_T0SZ(VA_BITS) // default T0SZ small enough?
+ b.ge 1f // .. then skip additional level
+
+ adrp x6, idmap_t0sz
+ str x5, [x6, :lo12:idmap_t0sz]
+
+ create_table_entry x0, x3, EXTRA_SHIFT, EXTRA_PTRS, x5, x6
+1:
+#endif
+
create_pgd_entry x0, x3, x5, x6
ldr x6, =KERNEL_END
mov x5, x3 // __pa(KERNEL_START)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 328b8ce4b007..74554dfcce73 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -151,6 +151,7 @@ asmlinkage void secondary_start_kernel(void)
*/
cpu_set_reserved_ttbr0();
flush_tlb_all();
+ cpu_set_default_tcr_t0sz();
preempt_disable();
trace_hardirqs_off();
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index c6daaf6c6f97..c4f60393383e 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -40,6 +40,8 @@
#include "mm.h"
+u64 idmap_t0sz = TCR_T0SZ(VA_BITS);
+
/*
* Empty_zero_page is a special page that is used for zero-initialized data
* and COW.
@@ -454,6 +456,7 @@ void __init paging_init(void)
*/
cpu_set_reserved_ttbr0();
flush_tlb_all();
+ cpu_set_default_tcr_t0sz();
}
/*
@@ -461,8 +464,10 @@ void __init paging_init(void)
*/
void setup_mm_for_reboot(void)
{
- cpu_switch_mm(idmap_pg_dir, &init_mm);
+ cpu_set_reserved_ttbr0();
flush_tlb_all();
+ cpu_set_idmap_tcr_t0sz();
+ cpu_switch_mm(idmap_pg_dir, &init_mm);
}
/*
diff --git a/arch/arm64/mm/proc-macros.S b/arch/arm64/mm/proc-macros.S
index 005d29e2977d..c17fdd6a19bc 100644
--- a/arch/arm64/mm/proc-macros.S
+++ b/arch/arm64/mm/proc-macros.S
@@ -52,3 +52,14 @@
mov \reg, #4 // bytes per word
lsl \reg, \reg, \tmp // actual cache line size
.endm
+
+/*
+ * tcr_set_idmap_t0sz - update TCR.T0SZ so that we can load the ID map
+ */
+ .macro tcr_set_idmap_t0sz, valreg, tmpreg
+#ifndef CONFIG_ARM64_VA_BITS_48
+ adrp \tmpreg, idmap_t0sz
+ ldr \tmpreg, [\tmpreg, #:lo12:idmap_t0sz]
+ bfi \valreg, \tmpreg, #TCR_T0SZ_OFFSET, #TCR_TxSZ_WIDTH
+#endif
+ .endm
diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index 28eebfb6af76..cdd754e19b9b 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -156,6 +156,7 @@ ENTRY(cpu_do_resume)
msr cpacr_el1, x6
msr ttbr0_el1, x1
msr ttbr1_el1, x7
+ tcr_set_idmap_t0sz x8, x7
msr tcr_el1, x8
msr vbar_el1, x9
msr mdscr_el1, x10
@@ -233,6 +234,8 @@ ENTRY(__cpu_setup)
*/
ldr x10, =TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
TCR_TG_FLAGS | TCR_ASID16 | TCR_TBI0
+ tcr_set_idmap_t0sz x10, x9
+
/*
* Read the PARange bits from ID_AA64MMFR0_EL1 and set the IPS bits in
* TCR_EL1.
--
1.8.3.2
More information about the linux-arm-kernel
mailing list