Re: Fwd: [Bug 213069] New: kernel BUG at arch/powerpc/include/asm/book3s/64/hash-4k.h:147! Oops: Exception in kernel mode, sig: 5 [#1]

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 5/17/21 11:25 AM, Aneesh Kumar K.V wrote:
> On 5/17/21 11:17 AM, Christophe Leroy wrote:
>> +aneesh
>> +linuxppc-dev list
>>
>> Le 17/05/2021 à 07:44, Anshuman Khandual a écrit :
>>> Hello Christophe,
>>>
>>> DEBUG_VM_PGTABLE has now been re-enabled on powerpc recently ? was not
>>> aware about this. From the error log, it failed explicitly on 4K page
>>> size hash config.
>>>
>>> static inline pmd_t hash__pmd_mkhuge(pmd_t pmd)
>>> {
>>>          BUG();        ------> Failed
>>>          return pmd;
>>> }
>>>
>>> static inline pmd_t __pmd_mkhuge(pmd_t pmd)
>>> {
>>>          if (radix_enabled())
>>>                  return radix__pmd_mkhuge(pmd);
>>>          return hash__pmd_mkhuge(pmd);
>>> }
>>>
>>> pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot)
>>> {
>>>          unsigned long pmdv;
>>>
>>>          pmdv = (pfn << PAGE_SHIFT) & PTE_RPN_MASK;
>>>
>>>          return __pmd_mkhuge(pmd_set_protbits(__pmd(pmdv), pgprot));
>>> }
>>>
>>> It seems like on powerpc, where pfn_pmd() makes a huge page but which
>>> is not supported on 4K hash config thus triggering the BUG(). But all
>>> pfn_pmd() call sites inside the debug_vm_pgtable() test are protected
>>> with CONFIG_TRANSPARENT_HUGEPAGE. IIUC unlike powerpc, pfn_pmd() does
>>> not directly make a huge page on other platforms.
>>>
>>> Looking at arch/powerpc/include/asm/book3s/64/hash-4k.h, all relevant
>>> THP helpers has BUG() or 0 which indicates THP might not be supported
>>> on 4K page size hash config ?
>>>
>>> But looking at arch/powerpc/platforms/Kconfig.cputype, it seems like
>>> HAVE_ARCH_TRANSPARENT_HUGEPAGE is invariably selected on PPC_BOOK3S_64
>>> platforms which I assume includes 4K page size hash config as well.
>>>
>>> Is THP some how getting enabled on this 4K page size hash config where
>>> it should not be (thus triggering the BUG) ? OR am I missing something
>>> here.
>>>
>>
> 
> We should put those  pfn_pmd()  and pfn_pud() after
> 
>     if (!has_transparent_hugepage())
>         return;

The following patch has been lightly tested on arm64 and x86 platforms.
Could you please verify if this solves the problem on powerpc 4K hash
config ? Thank you.

- Anshuman

 mm/debug_vm_pgtable.c | 58 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 48 insertions(+), 10 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index e2f35db8ba69..6ff92c8b0a00 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -146,13 +146,14 @@ static void __init pte_savedwrite_tests(unsigned long pfn, pgprot_t prot)
 static void __init pmd_basic_tests(unsigned long pfn, int idx)
 {
 	pgprot_t prot = protection_map[idx];
-	pmd_t pmd = pfn_pmd(pfn, prot);
 	unsigned long val = idx, *ptr = &val;
+	pmd_t pmd;
 
 	if (!has_transparent_hugepage())
 		return;
 
 	pr_debug("Validating PMD basic (%pGv)\n", ptr);
+	pmd = pfn_pmd(pfn, prot);
 
 	/*
 	 * This test needs to be executed after the given page table entry
@@ -232,9 +233,14 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
 
 static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pfn_pmd(pfn, prot);
+	pmd_t pmd;
+
+	if (!has_transparent_hugepage())
+		return;
 
 	pr_debug("Validating PMD leaf\n");
+	pmd = pfn_pmd(pfn, prot);
+
 	/*
 	 * PMD based THP is a leaf entry.
 	 */
@@ -244,12 +250,16 @@ static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)
 
 static void __init pmd_savedwrite_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pfn_pmd(pfn, prot);
+	pmd_t pmd;
 
 	if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
 		return;
 
+	if (!has_transparent_hugepage())
+		return;
+
 	pr_debug("Validating PMD saved write\n");
+	pmd = pfn_pmd(pfn, prot);
 	WARN_ON(!pmd_savedwrite(pmd_mk_savedwrite(pmd_clear_savedwrite(pmd))));
 	WARN_ON(pmd_savedwrite(pmd_clear_savedwrite(pmd_mk_savedwrite(pmd))));
 }
@@ -258,13 +268,14 @@ static void __init pmd_savedwrite_tests(unsigned long pfn, pgprot_t prot)
 static void __init pud_basic_tests(struct mm_struct *mm, unsigned long pfn, int idx)
 {
 	pgprot_t prot = protection_map[idx];
-	pud_t pud = pfn_pud(pfn, prot);
 	unsigned long val = idx, *ptr = &val;
+	pud_t pud;
 
 	if (!has_transparent_hugepage())
 		return;
 
 	pr_debug("Validating PUD basic (%pGv)\n", ptr);
+	pud = pfn_pud(pfn, prot);
 
 	/*
 	 * This test needs to be executed after the given page table entry
@@ -348,9 +359,13 @@ static void __init pud_advanced_tests(struct mm_struct *mm,
 
 static void __init pud_leaf_tests(unsigned long pfn, pgprot_t prot)
 {
-	pud_t pud = pfn_pud(pfn, prot);
+	pud_t pud;
+
+	if (!has_transparent_hugepage())
+		return;
 
 	pr_debug("Validating PUD leaf\n");
+	pud = pfn_pud(pfn, prot);
 	/*
 	 * PUD based THP is a leaf entry.
 	 */
@@ -642,12 +657,16 @@ static void __init pte_protnone_tests(unsigned long pfn, pgprot_t prot)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void __init pmd_protnone_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
+	pmd_t pmd;
 
 	if (!IS_ENABLED(CONFIG_NUMA_BALANCING))
 		return;
 
+	if (!has_transparent_hugepage())
+		return;
+
 	pr_debug("Validating PMD protnone\n");
+	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
 	WARN_ON(!pmd_protnone(pmd));
 	WARN_ON(!pmd_present(pmd));
 }
@@ -667,18 +686,26 @@ static void __init pte_devmap_tests(unsigned long pfn, pgprot_t prot)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void __init pmd_devmap_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pfn_pmd(pfn, prot);
+	pmd_t pmd;
+
+	if (!has_transparent_hugepage())
+		return;
 
 	pr_debug("Validating PMD devmap\n");
+	pmd = pfn_pmd(pfn, prot);
 	WARN_ON(!pmd_devmap(pmd_mkdevmap(pmd)));
 }
 
 #ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 static void __init pud_devmap_tests(unsigned long pfn, pgprot_t prot)
 {
-	pud_t pud = pfn_pud(pfn, prot);
+	pud_t pud;
+
+	if (!has_transparent_hugepage())
+		return;
 
 	pr_debug("Validating PUD devmap\n");
+	pud = pfn_pud(pfn, prot);
 	WARN_ON(!pud_devmap(pud_mkdevmap(pud)));
 }
 #else  /* !CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD */
@@ -721,25 +748,33 @@ static void __init pte_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static void __init pmd_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pfn_pmd(pfn, prot);
+	pmd_t pmd;
 
 	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY))
 		return;
 
+	if (!has_transparent_hugepage())
+		return;
+
 	pr_debug("Validating PMD soft dirty\n");
+	pmd = pfn_pmd(pfn, prot);
 	WARN_ON(!pmd_soft_dirty(pmd_mksoft_dirty(pmd)));
 	WARN_ON(pmd_soft_dirty(pmd_clear_soft_dirty(pmd)));
 }
 
 static void __init pmd_swap_soft_dirty_tests(unsigned long pfn, pgprot_t prot)
 {
-	pmd_t pmd = pfn_pmd(pfn, prot);
+	pmd_t pmd;
 
 	if (!IS_ENABLED(CONFIG_MEM_SOFT_DIRTY) ||
 		!IS_ENABLED(CONFIG_ARCH_ENABLE_THP_MIGRATION))
 		return;
 
+	if (!has_transparent_hugepage())
+		return;
+
 	pr_debug("Validating PMD swap soft dirty\n");
+	pmd = pfn_pmd(pfn, prot);
 	WARN_ON(!pmd_swp_soft_dirty(pmd_swp_mksoft_dirty(pmd)));
 	WARN_ON(pmd_swp_soft_dirty(pmd_swp_clear_soft_dirty(pmd)));
 }
@@ -768,6 +803,9 @@ static void __init pmd_swap_tests(unsigned long pfn, pgprot_t prot)
 	swp_entry_t swp;
 	pmd_t pmd;
 
+	if (!has_transparent_hugepage())
+		return;
+
 	pr_debug("Validating PMD swap\n");
 	pmd = pfn_pmd(pfn, prot);
 	swp = __pmd_to_swp_entry(pmd);
-- 
2.20.1