[PATCH v3] riscv: mm: Avoid spurious fault after hotplugging vmemmap

[Vivian Wang]

section_activate() does not flush TLB after populating new vmemmap
pages. On most architectures, this is okay. However it is a problem on
RISC-V since there the TLB caching non-present entries is permitted,
which causes spurious faults on some hardwares.

This seems to be most easily reproduced with DEBUG_VM=y and
PAGE_POISONING=y, which causes these newly mapped struct pages to be
poisoned i.e. written to immediately after mapping.

Add a hook vmemmap_populate_finalize() in __populate_section_memmap()
after population, to allow architectures to handle such situations as
needed. Then implement it on RISC-V to arrange for the existing
exception handler code to deal with these faults if they happen.

Signed-off-by: Vivian Wang <wangruikang@xxxxxxxxxxx>
---
Depends on my earlier kfence fixes for mark_new_valid_map() [1].

Found while testing AMD_HSA/ZONE_DEVICE on SpacemiT K3. Using
ZONE_DEVICE requires another fix [2].

[1]: https://lore.kernel.org/linux-riscv/20260303-handle-kfence-protect-spurious-fault-v2-0-f80d8354d79d@xxxxxxxxxxx
[2]: https://lore.kernel.org/linux-riscv/20260309-riscv-sparsemem-vmemmap-limits-v1-2-f40efe18e3cd@xxxxxxxxxxx
---
Changes in v3:
- Merged back into one patch (Mike)
- (No code changes otherwise.)
- Link to v2: https://patch.msgid.link/20260604-mark-after-vmemmap-populate-v2-0-ab6a7d03b434@xxxxxxxxxxx

Changes in v2:
- Split patch in two, hook point and riscv hook 
- Explain hook necessity in patch 1 message (Mike)
- Make hook #define based (Mike)
- Call finalize hook only on populate success
- Link to v1: https://patch.msgid.link/20260525-mark-after-vmemmap-populate-v1-1-e698d859ba16@xxxxxxxxxxx
---
 arch/riscv/include/asm/pgtable.h | 4 ++++
 arch/riscv/mm/init.c             | 6 ++++++
 mm/sparse-vmemmap.c              | 8 ++++++++
 3 files changed, 18 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index a1a7c6520a09..aa0f50e3d534 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -1243,6 +1243,10 @@ static inline pte_t pte_swp_clear_exclusive(pte_t pte)
 #define TASK_SIZE	FIXADDR_START
 #endif
 
+/* Needed on SPARSEMEM_VMEMMAP */
+#define vmemmap_populate_finalize vmemmap_populate_finalize
+void __meminit vmemmap_populate_finalize(void);
+
 #else /* CONFIG_MMU */
 
 #define PAGE_SHARED		__pgprot(0)
diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 706f43523935..cf9ae4099f82 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -1360,6 +1360,12 @@ int __meminit vmemmap_populate(unsigned long start, unsigned long end, int node,
 	 */
 	return vmemmap_populate_hugepages(start, end, node, altmap);
 }
+
+void __meminit vmemmap_populate_finalize(void)
+{
+	/* Avoid faults on cached non-present TLB entries. */
+	mark_new_valid_map();
+}
 #endif
 
 #if defined(CONFIG_MMU) && defined(CONFIG_64BIT)
diff --git a/mm/sparse-vmemmap.c b/mm/sparse-vmemmap.c
index 6eadb9d116e4..2a8b923fabe8 100644
--- a/mm/sparse-vmemmap.c
+++ b/mm/sparse-vmemmap.c
@@ -544,6 +544,12 @@ static int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
 
 #endif
 
+#ifndef vmemmap_populate_finalize
+static void __meminit vmemmap_populate_finalize(void)
+{
+}
+#endif
+
 struct page * __meminit __populate_section_memmap(unsigned long pfn,
 		unsigned long nr_pages, int nid, struct vmem_altmap *altmap,
 		struct dev_pagemap *pgmap)
@@ -564,6 +570,8 @@ struct page * __meminit __populate_section_memmap(unsigned long pfn,
 	if (r < 0)
 		return NULL;
 
+	vmemmap_populate_finalize();
+
 	return pfn_to_page(pfn);
 }
 

---
base-commit: 254f49634ee16a731174d2ae34bc50bd5f45e731
change-id: 20260525-mark-after-vmemmap-populate-68bd790839c9
prerequisite-message-id: <20260303-handle-kfence-protect-spurious-fault-v2-0-f80d8354d79d@xxxxxxxxxxx>
prerequisite-patch-id: fdc42f2647e21d111f44a6532887a6705cd470a9
prerequisite-patch-id: 096fa339c84c36643ae4311fd8362dc63e23d950
prerequisite-patch-id: 305c876a5f4a23a840a8142aea79b796ed297545
prerequisite-patch-id: d78cb55d6a616b1170f06a401c8fd44acd11e5d5
prerequisite-patch-id: b02b4a76e94f3e2821291d4c23b46f6e5ecf5203

Best regards,
--  
Vivian Wang <wangruikang@xxxxxxxxxxx>