[PATCH 08/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sh-X2

[Lorenzo Stoakes (ARM)]

Currently, non-x2 sh specifies CONFIG_MMU_GATHER_RCU_TABLE_FREE allowing
RCU page table freeing.

sh-X2 is problematic because it utilises slab-allocated PMD page tables,
and thus tlb_remove_ptdesc() cannot be used in these cases.

All other sh variants are fine as commit e3ecf7c7d082 ("mm: pgtable:
convert some architectures to use tlb_remove_ptdesc()") already converted
page table freeing to use tlb_remove_ptdesc(), which does so after an RCU
grace period when CONFIG_MMU_GATHER_RCU_TABLE_FREE is specified.

Resolve this issue by firstly specifying CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE
for sh-X2, so the arch can provide its own __tlb_remove_table()
implementation (called after the RCU grace period).

Then, convert __pmd_free_tlb() to tag the pointer to the PMD, and have
__tlb_remove_table() check this tag to determine whether to free via the
slab or to use pagetable_dtor_free().

This follows the pattern used by sparc64 as implemented in commit
4a0100f7546f ("sparc64: use RCU page table freeing").

Previously __pmd_free_tlb() freed PMD page tables immediately, before any
TLB flush IPI. This seems to be a pre-existing bug, which this change also
resolves.

CONFIG_HAVE_ARCH_TLB_REMOVE_TABLE is only specified for sh-X2, as setting
it disables CONFIG_PT_RECLAIM and causes __tlb_remove_table_one() to call
tlb_remove_table_sync_rcu() and synchronize_rcu() in turn, and this is not
necessary for other sh variants.

This forms part of an overall effort to switch every architecture to this
mode.

Signed-off-by: Lorenzo Stoakes (ARM) <ljs@xxxxxxxxxx>
---
 arch/sh/Kconfig               |  3 ++-
 arch/sh/include/asm/pgalloc.h |  6 +++++-
 arch/sh/mm/pgtable.c          | 20 ++++++++++++++++++++
 3 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/arch/sh/Kconfig b/arch/sh/Kconfig
index 204f64912f0e..75236bef6f16 100644
--- a/arch/sh/Kconfig
+++ b/arch/sh/Kconfig
@@ -33,6 +33,7 @@ config SUPERH
 	select HAVE_ARCH_AUDITSYSCALL
 	select HAVE_ARCH_KGDB
 	select HAVE_ARCH_SECCOMP_FILTER
+	select HAVE_ARCH_TLB_REMOVE_TABLE if X2TLB
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_DEBUG_BUGVERBOSE
 	select HAVE_DEBUG_KMEMLEAK
@@ -61,7 +62,7 @@ config SUPERH
 	select HAVE_SYSCALL_TRACEPOINTS
 	select IRQ_FORCED_THREADING
 	select LOCK_MM_AND_FIND_VMA
-	select MMU_GATHER_RCU_TABLE_FREE if MMU && !X2TLB
+	select MMU_GATHER_RCU_TABLE_FREE if MMU
 	select MODULES_USE_ELF_RELA
 	select NEED_SG_DMA_LENGTH
 	select NO_DMA if !MMU && !DMA_COHERENT
diff --git a/arch/sh/include/asm/pgalloc.h b/arch/sh/include/asm/pgalloc.h
index 6fe7123d38fa..67ce7fa23fa1 100644
--- a/arch/sh/include/asm/pgalloc.h
+++ b/arch/sh/include/asm/pgalloc.h
@@ -17,7 +17,11 @@ extern void pgd_free(struct mm_struct *mm, pgd_t *pgd);
 extern void pud_populate(struct mm_struct *mm, pud_t *pudp, pmd_t *pmd);
 extern pmd_t *pmd_alloc_one(struct mm_struct *mm, unsigned long address);
 extern void pmd_free(struct mm_struct *mm, pmd_t *pmd);
-#define __pmd_free_tlb(tlb, pmdp, addr)		pmd_free((tlb)->mm, (pmdp))
+extern void __tlb_remove_table(void *table);
+
+/* PMDs are slab-allocated, tag so they are freed correctly. */
+#define __pmd_free_tlb(tlb, pmdp, addr)					\
+	tlb_remove_table((tlb), (void *)((unsigned long)(pmdp) | 1))
 #endif
 
 static inline void pmd_populate_kernel(struct mm_struct *mm, pmd_t *pmd,
diff --git a/arch/sh/mm/pgtable.c b/arch/sh/mm/pgtable.c
index 3a4085ea0161..f6184b86b89c 100644
--- a/arch/sh/mm/pgtable.c
+++ b/arch/sh/mm/pgtable.c
@@ -56,4 +56,24 @@ void pmd_free(struct mm_struct *mm, pmd_t *pmd)
 {
 	kmem_cache_free(pmd_cachep, pmd);
 }
+
+static void __tlb_remove_table_slab(void *table)
+{
+	kmem_cache_free(pmd_cachep, table);
+}
+
+static void __tlb_remove_table_pgtable(void *table)
+{
+	pagetable_dtor_free(table);
+}
+
+void __tlb_remove_table(void *table)
+{
+	const unsigned long addr = (unsigned long)table;
+
+	if (addr & 1)
+		__tlb_remove_table_slab((void *)(addr & ~1UL));
+	else
+		__tlb_remove_table_pgtable(table);
+}
 #endif /* PAGETABLE_LEVELS > 2 */

-- 
2.55.0