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enabling kvm w/SPLIT_PTLOCK_CPUS > NR_CPUS fails to build in pgtable.c

DISCUSSION Martin Schwidefsky 1 participant 1 message Jan 5, 2015 1 message not in the archive s390

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Martin Schwidefsky

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Quoted 44 lines · On Fri, 2 Jan 2015 11:31:36 +0100 Heiko Carstens <[email protected]>…
Quoted 22 lines · Mike Frysinger

i've configured my kernel to have:
CONFIG_KVM=y
CONFIG_NR_CPUS=2
CONFIG_SPLIT_PTLOCK_CPUS=4

and that makes the build very unhappy:

	  CC      arch/s390/mm/pgtable.o
	arch/s390/mm/pgtable.c: In function ���__gmap_segment_gaddr���:
	arch/s390/mm/pgtable.c:327:2: error: implicit declaration of function 
	���pmd_to_page��� [-Werror=implicit-function-declaration]
	  page = pmd_to_page((pmd_t *) entry);
	  ^

this is because include/linux/mm_types.h has:

	#define USE_SPLIT_PMD_PTLOCKS	(USE_SPLIT_PTE_PTLOCKS && \
			IS_ENABLED(CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK))

and include/linux/mm.h has:

	#if USE_SPLIT_PMD_PTLOCKS
	static struct page *pmd_to_page(pmd_t *pmd)
	...
Quoted 6 lines

i did set NR_CPUS down on purpose (this system only has two cpus), but apparently tweaking SPLIT_PTLOCK_CPUS isn't an option :). in mm/Kconfig:

	config SPLIT_PTLOCK_CPUS
		int
		default "4"

-mike

Thanks for reporting. The patch below should fix it (adding Martin to To:)

include/linux/mm.h +1 -3
index f80d0194c9bc..4ee25aea7861 100644
@@ -1555,14 +1555,14 @@ static inline void pgtable_page_dtor(struct page *page)
 	((unlikely(pmd_none(*(pmd))) && __pte_alloc_kernel(pmd, address))? \
 		NULL: pte_offset_kernel(pmd, address))
 
-#if USE_SPLIT_PMD_PTLOCKS
-
-static struct page *pmd_to_page(pmd_t *pmd)
+static inline struct page *pmd_to_page(pmd_t *pmd)

include/linux/mm.h static inline void pgtable_page_dtor(struct page *page) · line 1568

Quoted 10 lines
include/linux/mm.h +2 -0
 {
 	unsigned long mask = ~(PTRS_PER_PMD * sizeof(pmd_t) - 1);
 	return virt_to_page((void *)((unsigned long) pmd & mask));
 }
 
+#if USE_SPLIT_PMD_PTLOCKS
+
 static inline spinlock_t *pmd_lockptr(struct mm_struct *mm, pmd_t *pmd)
 {
 	return ptlock_ptr(pmd_to_page(pmd));

That looks good, there is no reason why the pmd_to_page helper should be conditional on the USE_SPLIT_PMD_PTLOCKS define.

Signature · 4 lines
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.