armv7: mmu: Make fine grained page tables work across stages
Among its other restrictions (which are noted in a comment above the
function prototype and stay in place), our makeshift fine-grained page
table support for ARM32 has the undocumented feature that it relies on
a global bookkeeping variable, causing all sorts of fun surprises when
you try to use it from multiple stages during the same boot. This patch
redesigns the bookkeeping to stay completely inline in the (persistent)
TTB which should resolve the issue. (This had not been a problem on any
of our platforms for now... I just noticed this because I was trying to
solve the same issue on ARM64.)
BRANCH=None
BUG=None
TEST=Booted veyron_jerry. Mapped a second fine-grained memory range
from romstage, confirmed that it finds the next free spot and leaves the
bootblock table in place.
Change-Id: I325866828b4ff251142e1131ce78b571edcc9cf9
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/302955
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
diff --git a/src/arch/arm/armv7/mmu.c b/src/arch/arm/armv7/mmu.c
index 727da5c..8c2f78c 100644
--- a/src/arch/arm/armv7/mmu.c
+++ b/src/arch/arm/armv7/mmu.c
@@ -97,13 +97,17 @@
typedef uint32_t pte_t;
#endif /* CONFIG_ARM_LPAE */
+/* We set the first PTE to a sentinel value that cannot occur naturally (has
+ * attributes set but bits [1:0] are 0 -> unmapped) to mark unused subtables. */
+#define ATTR_UNUSED 0xBADbA6E0
+#define SUBTABLE_PTES (1 << (BLOCK_SHIFT - PAGE_SHIFT))
+
/*
* mask/shift/size for pages and blocks
*/
#define PAGE_SHIFT 12
#define PAGE_SIZE (1UL << PAGE_SHIFT)
#define BLOCK_SIZE (1UL << BLOCK_SHIFT)
-#define SUBTABLE_SIZE ((1 << (BLOCK_SHIFT - PAGE_SHIFT)) * sizeof(pte_t))
/*
* MAIR Index
@@ -113,7 +117,6 @@
#define MAIR_INDX_WB 2
static pte_t *const ttb_buff = (void *)_ttb;
-static int used_tables = 0;
/* Not all boards want to use subtables and declare them in memlayout.ld. This
* outputs two 0x00000000 symbols if they don't, making _ttb_subtables_size 0.
@@ -156,12 +159,17 @@
static pte_t *mmu_create_subtable(pte_t *pgd_entry)
{
- if (used_tables >= _ttb_subtables_size / SUBTABLE_SIZE)
- die("Not enough room for another sub-pagetable!");
+ pte_t *table = (pte_t *)_ttb_subtables;
+
+ /* Find unused subtable (first PTE == ATTR_UNUSED). */
+ while (table[0] != ATTR_UNUSED) {
+ table += SUBTABLE_PTES;
+ if ((pte_t *)_ettb_subtables - table <= 0)
+ die("Not enough room for another sub-pagetable!");
+ }
/* We assume that *pgd_entry must already be a valid block mapping. */
uintptr_t start_addr = (uintptr_t)(*pgd_entry & BLOCK_MASK);
- pte_t *table = (void *)(_ttb_subtables + used_tables++ * SUBTABLE_SIZE);
printk(BIOS_DEBUG, "Creating new subtable @%p for [%#.8x:%#.8lx)\n",
table, start_addr, start_addr + BLOCK_SIZE);
@@ -172,8 +180,7 @@
attr = ((attr & ~(1 << 4)) | (1 << 0));
if (attr & ATTR_BLOCK)
attr = (attr & ~ATTR_BLOCK) | ATTR_PAGE;
- mmu_fill_table(table, 0, SUBTABLE_SIZE / sizeof(pte_t),
- start_addr, PAGE_SHIFT, attr);
+ mmu_fill_table(table, 0, SUBTABLE_PTES, start_addr, PAGE_SHIFT, attr);
/* Replace old entry in upper level table to point at subtable. */
*pgd_entry = (pte_t)(uintptr_t)table | ATTR_NEXTLEVEL;
@@ -265,6 +272,11 @@
*/
void mmu_init(void)
{
+ /* Initially mark all subtables as unused (first PTE == ATTR_UNUSED). */
+ pte_t *table = (pte_t *)_ttb_subtables;
+ for (; (pte_t *)_ettb_subtables - table > 0; table += SUBTABLE_PTES)
+ table[0] = ATTR_UNUSED;
+
if (CONFIG_ARM_LPAE) {
pte_t *const pgd_buff = (pte_t*)(_ttb + 16*KiB);
pte_t *pmd = ttb_buff;
diff --git a/src/arch/arm/include/armv7/arch/cache.h b/src/arch/arm/include/armv7/arch/cache.h
index 6e5dfb0..9549324 100644
--- a/src/arch/arm/include/armv7/arch/cache.h
+++ b/src/arch/arm/include/armv7/arch/cache.h
@@ -385,7 +385,8 @@
* Generalized setup/init functions
*/
-/* mmu initialization (set page table address, set permissions, etc) */
+/* MMU initialization (set page table base, permissions, initialize subtable
+ * buffer, etc.). Must only be called ONCE PER BOOT, before any mappings. */
void mmu_init(void);
enum dcache_policy {
