From: Bharata B Rao <bhar...@linux.ibm.com>
We split the page table mapping on memory unplug if the
linear range was mapped with huge page mapping (for ex: 1G)
The page table splitting code has a few issues:
1. Recursive locking
--------------------
Memory unplug path takes cpu_hotplug_lock and calls stop_machine()
for splitting the mappings. However stop_machine() takes
cpu_hotplug_lock again causing deadlock.
2. BUG: sleeping function called from in_atomic() context
---------------------------------------------------------
Memory unplug path (remove_pagetable) takes init_mm.page_table_lock
spinlock and later calls stop_machine() which does wait_for_completion()
3. Bad unlock unbalance
-----------------------
Memory unplug path takes init_mm.page_table_lock spinlock and calls
stop_machine(). The stop_machine thread function runs in a different
thread context (migration thread) which tries to release and reaquire
ptl. Releasing ptl from a different thread than which acquired it
causes bad unlock unbalance.
These problems can be avoided if we avoid mapping hot-plugged memory
with 1G mapping, thereby removing the need for splitting them during
unplug. The kernel always make sure the minimum unplug request is
SUBSECTION_SIZE for device memory and SECTION_SIZE for regular memory.
In preparation for such a change remove page table splitting support.
This essentially is a revert of
commit 4dd5f8a99e791 ("powerpc/mm/radix: Split linear mapping on hot-unplug")
Signed-off-by: Bharata B Rao <bhar...@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
---
arch/powerpc/mm/book3s64/radix_pgtable.c | 95 +++++-------------------
1 file changed, 19 insertions(+), 76 deletions(-)
diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c
b/arch/powerpc/mm/book3s64/radix_pgtable.c
index af57604f295f..78ad11812e0d 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -15,7 +15,6 @@
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/string_helpers.h>
-#include <linux/stop_machine.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -723,32 +722,6 @@ static void free_pud_table(pud_t *pud_start, p4d_t *p4d)
p4d_clear(p4d);
}
-struct change_mapping_params {
- pte_t *pte;
- unsigned long start;
- unsigned long end;
- unsigned long aligned_start;
- unsigned long aligned_end;
-};
-
-static int __meminit stop_machine_change_mapping(void *data)
-{
- struct change_mapping_params *params =
- (struct change_mapping_params *)data;
-
- if (!data)
- return -1;
-
- spin_unlock(&init_mm.page_table_lock);
- pte_clear(&init_mm, params->aligned_start, params->pte);
- create_physical_mapping(__pa(params->aligned_start),
- __pa(params->start), -1, PAGE_KERNEL);
- create_physical_mapping(__pa(params->end), __pa(params->aligned_end),
- -1, PAGE_KERNEL);
- spin_lock(&init_mm.page_table_lock);
- return 0;
-}
-
static void remove_pte_table(pte_t *pte_start, unsigned long addr,
unsigned long end)
{
@@ -777,52 +750,6 @@ static void remove_pte_table(pte_t *pte_start, unsigned
long addr,
}
}
-/*
- * clear the pte and potentially split the mapping helper
- */
-static void __meminit split_kernel_mapping(unsigned long addr, unsigned long
end,
- unsigned long size, pte_t *pte)
-{
- unsigned long mask = ~(size - 1);
- unsigned long aligned_start = addr & mask;
- unsigned long aligned_end = addr + size;
- struct change_mapping_params params;
- bool split_region = false;
-
- if ((end - addr) < size) {
- /*
- * We're going to clear the PTE, but not flushed
- * the mapping, time to remap and flush. The
- * effects if visible outside the processor or
- * if we are running in code close to the
- * mapping we cleared, we are in trouble.
- */
- if (overlaps_kernel_text(aligned_start, addr) ||
- overlaps_kernel_text(end, aligned_end)) {
- /*
- * Hack, just return, don't pte_clear
- */
- WARN_ONCE(1, "Linear mapping %lx->%lx overlaps kernel "
- "text, not splitting\n", addr, end);
- return;
- }
- split_region = true;
- }
-
- if (split_region) {
- params.pte = pte;
- params.start = addr;
- params.end = end;
- params.aligned_start = addr & ~(size - 1);
- params.aligned_end = min_t(unsigned long, aligned_end,
- (unsigned long)__va(memblock_end_of_DRAM()));
- stop_machine(stop_machine_change_mapping, ¶ms, NULL);
- return;
- }
-
- pte_clear(&init_mm, addr, pte);
-}
-
static void remove_pmd_table(pmd_t *pmd_start, unsigned long addr,
unsigned long end)
{
@@ -838,7 +765,12 @@ static void remove_pmd_table(pmd_t *pmd_start, unsigned
long addr,
continue;
if (pmd_is_leaf(*pmd)) {
- split_kernel_mapping(addr, end, PMD_SIZE, (pte_t *)pmd);
+ if (!IS_ALIGNED(addr, PMD_SIZE) ||
+ !IS_ALIGNED(next, PMD_SIZE)) {
+ WARN_ONCE(1, "%s: unaligned range\n", __func__);
+ continue;
+ }
+ pte_clear(&init_mm, addr, (pte_t *)pmd);
continue;
}
@@ -863,7 +795,12 @@ static void remove_pud_table(pud_t *pud_start, unsigned
long addr,
continue;
if (pud_is_leaf(*pud)) {
- split_kernel_mapping(addr, end, PUD_SIZE, (pte_t *)pud);
+ if (!IS_ALIGNED(addr, PUD_SIZE) ||
+ !IS_ALIGNED(next, PUD_SIZE)) {
+ WARN_ONCE(1, "%s: unaligned range\n", __func__);
+ continue;
+ }
+ pte_clear(&init_mm, addr, (pte_t *)pud);
continue;
}
@@ -891,7 +828,13 @@ static void __meminit remove_pagetable(unsigned long
start, unsigned long end)
continue;
if (p4d_is_leaf(*p4d)) {
- split_kernel_mapping(addr, end, P4D_SIZE, (pte_t *)p4d);
+ if (!IS_ALIGNED(addr, P4D_SIZE) ||
+ !IS_ALIGNED(next, P4D_SIZE)) {
+ WARN_ONCE(1, "%s: unaligned range\n", __func__);
+ continue;
+ }
+
+ pte_clear(&init_mm, addr, (pte_t *)pgd);
continue;
}
--
2.26.2
