Commit c1cc1552616d ("arm64: MMU initialisation") optimizes the
vmemmap to populate at the PMD section level which was suitable
initially since hotplugging granule is always 128M. However,
commit ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
which added 2M hotplugging granule disrupted the arm64 assumptions.
Considering the vmemmap_free -> unmap_hotplug_pmd_range path, when
pmd_sect() is true, the entire PMD section is cleared, even if there is
other effective subsection. For example pagemap1 and pagemap2 are part
of a single PMD entry and they are hot-added sequentially. Then pagemap1
is removed, vmemmap_free() will clear the entire PMD entry freeing the
struct page metadata for the whole section, even though pagemap2 is still
active.
To address the issue, we need to prevent PMD/PUD/CONT mappings for both
linear and vmemmap for non-boot sections if the size exceeds 2MB
(considering sub-section is 2MB). We only permit 2MB blocks in a 4KB page
configuration.
Cc: stable@xxxxxxxxxxxxxxx # v5.4+
Fixes: ba72b4c8cf60 ("mm/sparsemem: support sub-section hotplug")
Signed-off-by: Zhenhua Huang <quic_zhenhuah@xxxxxxxxxxx>
---
Hi Catalin and Anshuman,
Based on your review comments, I concluded below patch and tested with my setup.
I have not folded patchset #2 since this patch seems to be enough for backporting..
Please see if you have further suggestions.
arch/arm64/mm/mmu.c | 33 +++++++++++++++++++++++++++++----
1 file changed, 29 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index e2739b69e11b..2b4d23f01d85 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -42,9 +42,11 @@
#include <asm/pgalloc.h>
#include <asm/kfence.h>
-#define NO_BLOCK_MAPPINGS BIT(0)
+#define NO_PMD_BLOCK_MAPPINGS BIT(0)
#define NO_CONT_MAPPINGS BIT(1)
#define NO_EXEC_MAPPINGS BIT(2) /* assumes FEAT_HPDS is not used */
+#define NO_PUD_BLOCK_MAPPINGS BIT(3) /* Hotplug case: do not want block mapping for PUD */
+#define NO_BLOCK_MAPPINGS (NO_PMD_BLOCK_MAPPINGS | NO_PUD_BLOCK_MAPPINGS)
u64 kimage_voffset __ro_after_init;
EXPORT_SYMBOL(kimage_voffset);
@@ -254,7 +256,7 @@ static void init_pmd(pmd_t *pmdp, unsigned long addr, unsigned long end,
/* try section mapping first */
if (((addr | next | phys) & ~PMD_MASK) == 0 &&
- (flags & NO_BLOCK_MAPPINGS) == 0) {
+ (flags & NO_PMD_BLOCK_MAPPINGS) == 0) {
pmd_set_huge(pmdp, phys, prot);
/*
@@ -356,10 +358,11 @@ static void alloc_init_pud(p4d_t *p4dp, unsigned long addr, unsigned long end,
/*
* For 4K granule only, attempt to put down a 1GB block
+ * Hotplug case: do not attempt 1GB block
*/
if (pud_sect_supported() &&
((addr | next | phys) & ~PUD_MASK) == 0 &&
- (flags & NO_BLOCK_MAPPINGS) == 0) {
+ (flags & NO_PUD_BLOCK_MAPPINGS) == 0) {
pud_set_huge(pudp, phys, prot);
/*
@@ -1175,9 +1178,16 @@ int __meminit vmemmap_check_pmd(pmd_t *pmdp, int node,
int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
struct vmem_altmap *altmap)
{
+ unsigned long start_pfn;
+ struct mem_section *ms;
+
WARN_ON((start < VMEMMAP_START) || (end > VMEMMAP_END));
- if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES))
+ start_pfn = page_to_pfn((struct page *)start);
+ ms = __pfn_to_section(start_pfn);
+
+ /* Hotplugged section not support hugepages */
+ if (!IS_ENABLED(CONFIG_ARM64_4K_PAGES) || !early_section(ms))
return vmemmap_populate_basepages(start, end, node, altmap);
else
return vmemmap_populate_hugepages(start, end, node, altmap);
@@ -1339,9 +1349,24 @@ int arch_add_memory(int nid, u64 start, u64 size,
struct mhp_params *params)
{
int ret, flags = NO_EXEC_MAPPINGS;
+ unsigned long start_pfn = page_to_pfn((struct page *)start);
+ struct mem_section *ms = __pfn_to_section(start_pfn);
VM_BUG_ON(!mhp_range_allowed(start, size, true));
+ /* Should not be invoked by early section */
+ WARN_ON(early_section(ms));
+
+ if (IS_ENABLED(CONFIG_ARM64_4K_PAGES))
+ /*
+ * As per subsection granule is 2M, allow PMD block mapping in
+ * case 4K PAGES.
+ * Other cases forbid section mapping.
+ */
+ flags |= NO_PUD_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
+ else
+ flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
+
if (can_set_direct_map())
flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
--
2.25.1
