MMUv3 initialization sequence¶
The code in the initialize_mmu macro sets up MMUv3 memory mapping identically to MMUv2 fixed memory mapping. Depending on CONFIG_INITIALIZE_XTENSA_MMU_INSIDE_VMLINUX symbol this code is located in addresses it was linked for (symbol undefined), or not (symbol defined), so it needs to be position-independent.
The code has the following assumptions:
- This code fragment is run only on an MMU v3.
- TLBs are in their reset state.
- ITLBCFG and DTLBCFG are zero (reset state).
- RASID is 0x04030201 (reset state).
- PS.RING is zero (reset state).
- LITBASE is zero (reset state, PC-relative literals); required to be PIC.
TLB setup proceeds along the following steps.
Legend:
- VA = virtual address (two upper nibbles of it);
- PA = physical address (two upper nibbles of it);
- pc = physical range that contains this code;
After step 2, we jump to virtual address in the range 0x40000000..0x5fffffff or 0x00000000..0x1fffffff, depending on whether the kernel was loaded below 0x40000000 or above. That address corresponds to next instruction to execute in this code. After step 4, we jump to intended (linked) address of this code. The scheme below assumes that the kernel is loaded below 0x40000000.
Step0 Step1 Step2 Step3 Step4 Step5 VA PA PA PA PA VA PA PA E0..FF -> E0 -> E0 -> E0 F0..FF -> F0 -> F0 C0..DF -> C0 -> C0 -> C0 E0..EF -> F0 -> F0 A0..BF -> A0 -> A0 -> A0 D8..DF -> 00 -> 00 80..9F -> 80 -> 80 -> 80 D0..D7 -> 00 -> 00 60..7F -> 60 -> 60 -> 60 40..5F -> 40 -> pc -> pc 40..5F -> pc 20..3F -> 20 -> 20 -> 20 00..1F -> 00 -> 00 -> 00
The default location of IO peripherals is above 0xf0000000. This may be changed using a “ranges” property in a device tree simple-bus node. See the Devicetree Specification, section 4.5 for details on the syntax and semantics of simple-bus nodes. The following limitations apply:
- Only top level simple-bus nodes are considered
- Only one (first) simple-bus node is considered
- Empty “ranges” properties are not supported
- Only the first triplet in the “ranges” property is considered
- The parent-bus-address value is rounded down to the nearest 256MB boundary
- The IO area covers the entire 256MB segment of parent-bus-address; the “ranges” triplet length field is ignored
MMUv3 address space layouts.¶
Default MMUv2-compatible layout:
Symbol VADDR Size
+------------------+
| Userspace | 0x00000000 TASK_SIZE
+------------------+ 0x40000000
+------------------+
| Page table | XCHAL_PAGE_TABLE_VADDR 0x80000000 XCHAL_PAGE_TABLE_SIZE
+------------------+
| KASAN shadow map | KASAN_SHADOW_START 0x80400000 KASAN_SHADOW_SIZE
+------------------+ 0x8e400000
+------------------+
| VMALLOC area | VMALLOC_START 0xc0000000 128MB - 64KB
+------------------+ VMALLOC_END
+------------------+
| Cache aliasing | TLBTEMP_BASE_1 0xc8000000 DCACHE_WAY_SIZE
| remap area 1 |
+------------------+
| Cache aliasing | TLBTEMP_BASE_2 DCACHE_WAY_SIZE
| remap area 2 |
+------------------+
+------------------+
| KMAP area | PKMAP_BASE PTRS_PER_PTE *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
| | (4MB * DCACHE_N_COLORS)
+------------------+
| Atomic KMAP area | FIXADDR_START KM_TYPE_NR *
| | NR_CPUS *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
+------------------+ FIXADDR_TOP 0xcffff000
+------------------+
| Cached KSEG | XCHAL_KSEG_CACHED_VADDR 0xd0000000 128MB
+------------------+
| Uncached KSEG | XCHAL_KSEG_BYPASS_VADDR 0xd8000000 128MB
+------------------+
| Cached KIO | XCHAL_KIO_CACHED_VADDR 0xe0000000 256MB
+------------------+
| Uncached KIO | XCHAL_KIO_BYPASS_VADDR 0xf0000000 256MB
+------------------+
256MB cached + 256MB uncached layout:
Symbol VADDR Size
+------------------+
| Userspace | 0x00000000 TASK_SIZE
+------------------+ 0x40000000
+------------------+
| Page table | XCHAL_PAGE_TABLE_VADDR 0x80000000 XCHAL_PAGE_TABLE_SIZE
+------------------+
| KASAN shadow map | KASAN_SHADOW_START 0x80400000 KASAN_SHADOW_SIZE
+------------------+ 0x8e400000
+------------------+
| VMALLOC area | VMALLOC_START 0xa0000000 128MB - 64KB
+------------------+ VMALLOC_END
+------------------+
| Cache aliasing | TLBTEMP_BASE_1 0xa8000000 DCACHE_WAY_SIZE
| remap area 1 |
+------------------+
| Cache aliasing | TLBTEMP_BASE_2 DCACHE_WAY_SIZE
| remap area 2 |
+------------------+
+------------------+
| KMAP area | PKMAP_BASE PTRS_PER_PTE *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
| | (4MB * DCACHE_N_COLORS)
+------------------+
| Atomic KMAP area | FIXADDR_START KM_TYPE_NR *
| | NR_CPUS *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
+------------------+ FIXADDR_TOP 0xaffff000
+------------------+
| Cached KSEG | XCHAL_KSEG_CACHED_VADDR 0xb0000000 256MB
+------------------+
| Uncached KSEG | XCHAL_KSEG_BYPASS_VADDR 0xc0000000 256MB
+------------------+
+------------------+
| Cached KIO | XCHAL_KIO_CACHED_VADDR 0xe0000000 256MB
+------------------+
| Uncached KIO | XCHAL_KIO_BYPASS_VADDR 0xf0000000 256MB
+------------------+
512MB cached + 512MB uncached layout:
Symbol VADDR Size
+------------------+
| Userspace | 0x00000000 TASK_SIZE
+------------------+ 0x40000000
+------------------+
| Page table | XCHAL_PAGE_TABLE_VADDR 0x80000000 XCHAL_PAGE_TABLE_SIZE
+------------------+
| KASAN shadow map | KASAN_SHADOW_START 0x80400000 KASAN_SHADOW_SIZE
+------------------+ 0x8e400000
+------------------+
| VMALLOC area | VMALLOC_START 0x90000000 128MB - 64KB
+------------------+ VMALLOC_END
+------------------+
| Cache aliasing | TLBTEMP_BASE_1 0x98000000 DCACHE_WAY_SIZE
| remap area 1 |
+------------------+
| Cache aliasing | TLBTEMP_BASE_2 DCACHE_WAY_SIZE
| remap area 2 |
+------------------+
+------------------+
| KMAP area | PKMAP_BASE PTRS_PER_PTE *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
| | (4MB * DCACHE_N_COLORS)
+------------------+
| Atomic KMAP area | FIXADDR_START KM_TYPE_NR *
| | NR_CPUS *
| | DCACHE_N_COLORS *
| | PAGE_SIZE
+------------------+ FIXADDR_TOP 0x9ffff000
+------------------+
| Cached KSEG | XCHAL_KSEG_CACHED_VADDR 0xa0000000 512MB
+------------------+
| Uncached KSEG | XCHAL_KSEG_BYPASS_VADDR 0xc0000000 512MB
+------------------+
| Cached KIO | XCHAL_KIO_CACHED_VADDR 0xe0000000 256MB
+------------------+
| Uncached KIO | XCHAL_KIO_BYPASS_VADDR 0xf0000000 256MB
+------------------+