[PATCH] powerpc/mm/hugetlb: Use the correct page size when flushing hugepage tlb

We used wrong page size (mmu_virtual_psize) when doing a tlbflush after
pte update. This patch update the flush to use hugetlb page size.
The page size is derived from hugetlb hstate.

Now that ptep_set_access_flags won't be called for hugetlb remove
the is_vm_hugetlb_page() check and add the assert of pte lock
unconditionally.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/include/asm/hugetlb.h | 19 +++--------------
 arch/powerpc/mm/pgtable.c          | 33 ++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 18 deletions(-)

diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
index 78540c074d70..b4404a6da74f 100644
--- a/arch/powerpc/include/asm/hugetlb.h
+++ b/arch/powerpc/include/asm/hugetlb.h

@@ -166,22 +166,9 @@ static inline pte_t huge_pte_wrprotect(pte_t pte)
 	return pte_wrprotect(pte);
 }
 
-static inline int huge_ptep_set_access_flags(struct vm_area_struct *vma,
-					     unsigned long addr, pte_t *ptep,
-					     pte_t pte, int dirty)
-{
-#ifdef HUGETLB_NEED_PRELOAD
-	/*
-	 * The "return 1" forces a call of update_mmu_cache, which will write a
-	 * TLB entry.  Without this, platforms that don't do a write of the TLB
-	 * entry in the TLB miss handler asm will fault ad infinitum.
-	 */
-	ptep_set_access_flags(vma, addr, ptep, pte, dirty);
-	return 1;
-#else
-	return ptep_set_access_flags(vma, addr, ptep, pte, dirty);
-#endif
-}
+extern int huge_ptep_set_access_flags(struct vm_area_struct *vma,
+				      unsigned long addr, pte_t *ptep,
+				      pte_t pte, int dirty);
 
 static inline pte_t huge_ptep_get(pte_t *ptep)
 {

diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index 9f361ae571e9..e70af9939379 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c

@@ -221,14 +221,43 @@ int ptep_set_access_flags(struct vm_area_struct *vma, unsigned long address,
 	entry = set_access_flags_filter(entry, vma, dirty);
 	changed = !pte_same(*(ptep), entry);
 	if (changed) {
-		if (!is_vm_hugetlb_page(vma))
-			assert_pte_locked(vma->vm_mm, address);
+		assert_pte_locked(vma->vm_mm, address);
 		__ptep_set_access_flags(vma->vm_mm, ptep, entry, address);
 		flush_tlb_page(vma, address);
 	}
 	return changed;
 }
 
+#ifdef CONFIG_HUGETLB_PAGE
+extern int huge_ptep_set_access_flags(struct vm_area_struct *vma,
+				      unsigned long addr, pte_t *ptep,
+				      pte_t pte, int dirty)
+{
+#ifdef HUGETLB_NEED_PRELOAD
+	/*
+	 * The "return 1" forces a call of update_mmu_cache, which will write a
+	 * TLB entry.  Without this, platforms that don't do a write of the TLB
+	 * entry in the TLB miss handler asm will fault ad infinitum.
+	 */
+	ptep_set_access_flags(vma, addr, ptep, pte, dirty);
+	return 1;
+#else
+	int changed;
+
+	pte = set_access_flags_filter(pte, vma, dirty);
+	changed = !pte_same(*(ptep), pte);
+	if (changed) {
+#ifdef CONFIG_DEBUG_VM
+		assert_spin_locked(&vma->vm_mm->page_table_lock);
+#endif
+		__ptep_set_access_flags(vma->vm_mm, ptep, pte, addr);
+		flush_hugetlb_page(vma, addr);
+	}
+	return changed;
+#endif
+}
+#endif /* CONFIG_HUGETLB_PAGE */
+
 #ifdef CONFIG_DEBUG_VM
 void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
 {

-- 
2.17.0

On Tue, 22 May 2018 14:42:09 +0530
"Aneesh Kumar K.V" [off-list ref] wrote:

We used wrong page size (mmu_virtual_psize) when doing a tlbflush after
pte update. This patch update the flush to use hugetlb page size.
The page size is derived from hugetlb hstate.

Now that ptep_set_access_flags won't be called for hugetlb remove
the is_vm_hugetlb_page() check and add the assert of pte lock
unconditionally.

radix__flush_tlb_page seems to check for a hugepage vma and flush the
right page size in that case. So is there a case where the flush size
actually goes wrong?

I do think if we could make hugetlb flushing always use
flush_hugetlb_page version and take the test out of flush_tlb_page I
think that would be nicer code (I haven't checked if that's feasible
after this patch), but that wouldn't be a bug-fix.

Thanks,
Nick

"Aneesh Kumar K.V" [off-list ref] writes:

We used wrong page size (mmu_virtual_psize) when doing a tlbflush after
pte update. This patch update the flush to use hugetlb page size.
The page size is derived from hugetlb hstate.

This sounds bad. Or is it not for some reason?

Either way a Fixes tag would be nice. Maybe:

  Fixes: b3603e174fc8 ("powerpc/mm: update radix__ptep_set_access_flag to not do full mm tlb flush")

I think this is only a problem on Radix, but the change log doesn't say.

cheers

On Tue, 29 May 2018 11:33:56 +1000
Michael Ellerman [off-list ref] wrote:

"Aneesh Kumar K.V" [off-list ref] writes:

quoted

We used wrong page size (mmu_virtual_psize) when doing a tlbflush after
pte update. This patch update the flush to use hugetlb page size.
The page size is derived from hugetlb hstate.  

This sounds bad. Or is it not for some reason?

It's not all that bad because the flush is mostly superfluous (one of
my tlbie optimisation patches gets rid of it except for accelerators).

Either way a Fixes tag would be nice. Maybe:

  Fixes: b3603e174fc8 ("powerpc/mm: update radix__ptep_set_access_flag to not do full mm tlb flush")

I think this is only a problem on Radix, but the change log doesn't say.

huge_ptep_set_access_flags->ptep_set_access_flags->flush_tlb_page->

void radix__flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr)
{
#ifdef CONFIG_HUGETLB_PAGE
        if (is_vm_hugetlb_page(vma))
                return radix__flush_hugetlb_page(vma, vmaddr);
#endif
        radix__flush_tlb_page_psize(vma->vm_mm, vmaddr, mmu_virtual_psize);
}

So I'm still not sure how the size is going wrong here. What am I
missig?

Thanks,
Nick

On 05/29/2018 07:39 AM, Nicholas Piggin wrote:

On Tue, 29 May 2018 11:33:56 +1000
Michael Ellerman [off-list ref] wrote:

quoted

"Aneesh Kumar K.V" [off-list ref] writes:

quoted

We used wrong page size (mmu_virtual_psize) when doing a tlbflush after
pte update. This patch update the flush to use hugetlb page size.
The page size is derived from hugetlb hstate.

This sounds bad. Or is it not for some reason?

It's not all that bad because the flush is mostly superfluous (one of
my tlbie optimisation patches gets rid of it except for accelerators).

quoted

Either way a Fixes tag would be nice. Maybe:

   Fixes: b3603e174fc8 ("powerpc/mm: update radix__ptep_set_access_flag to not do full mm tlb flush")

I think this is only a problem on Radix, but the change log doesn't say.

huge_ptep_set_access_flags->ptep_set_access_flags->flush_tlb_page->

void radix__flush_tlb_page(struct vm_area_struct *vma, unsigned long vmaddr)
{
#ifdef CONFIG_HUGETLB_PAGE
         if (is_vm_hugetlb_page(vma))
                 return radix__flush_hugetlb_page(vma, vmaddr);
#endif
         radix__flush_tlb_page_psize(vma->vm_mm, vmaddr, mmu_virtual_psize);
}

So I'm still not sure how the size is going wrong here. What am I
missig?

My mistake, I didn't look at the radix expansion. I was looking at 
huge_ptep_clear_flush() where we use flush_hugetlb_page().

-aneesh