Under some circumstances (e.g. debugging) it may be useful to have all
kernel memory mapped using PAGE_SIZE pages. Add an option for this.
Signed-off-by: Laura Abbott <labb...@fedoraproject.org>
---
arch/arm64/Kconfig | 11 +++++++++++
arch/arm64/mm/mmu.c | 10 +++++++---
2 files changed, 18 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index ffa3c54..faf7eac 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -504,6 +504,17 @@ config HOTPLUG_CPU
Say Y here to experiment with turning CPUs off and on. CPUs
can be controlled through /sys/devices/system/cpu.
+config FORCE_PAGES
+ bool "Force all memory mappings to be PAGE_SIZE"
+ help
+ For performance reasons, kernel memory may be mapped with
+ page table entries larger than the expected PAGE_SIZE. This results
+ in better TLB performance but prevents adjustment of page table
+ attributes at runtime. Say Y here to have all kernel memory mapped
+ with PAGE_SIZE entries.
+
+ If unsure, say N.
+
source kernel/Kconfig.preempt
source kernel/Kconfig.hz
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 2d6e7cf..450d38a 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -181,7 +181,8 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr,
unsigned long end,
do {
next = pmd_addr_end(addr, end);
/* try section mapping first */
- if (((addr | next | phys) & ~SECTION_MASK) == 0) {
+ if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
+ (!IS_ENABLED(CONFIG_FORCE_PAGES) || !pgtable_alloc)) {
pmd_t old_pmd =*pmd;
set_pmd(pmd, __pmd(phys |
pgprot_val(mk_sect_prot(prot))));
@@ -208,8 +209,11 @@ static void alloc_init_pmd(pud_t *pud, unsigned long addr,
unsigned long end,
}
static inline bool use_1G_block(unsigned long addr, unsigned long next,
- unsigned long phys)
+ unsigned long phys, phys_addr_t (*pgtable_alloc)(void))
{
+ if (pgtable_alloc && IS_ENABLED(CONFIG_FORCE_PAGES))
+ return false;
+
if (PAGE_SHIFT != 12)
return false;
@@ -241,7 +245,7 @@ static void alloc_init_pud(pgd_t *pgd, unsigned long addr,
unsigned long end,
/*
* For 4K granule only, attempt to put down a 1GB block
*/
- if (use_1G_block(addr, next, phys)) {
+ if (use_1G_block(addr, next, phys, pgtable_alloc)) {
pud_t old_pud = *pud;
set_pud(pud, __pud(phys |
pgprot_val(mk_sect_prot(prot))));
--
2.5.0
