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Message-ID: <877fyugrmc.fsf@linux.vnet.ibm.com>
Date: Mon, 17 Nov 2014 13:56:19 +0530
From: "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To: Mel Gorman <mgorman@...e.de>,
Linux Kernel <linux-kernel@...r.kernel.org>
Cc: Linux-MM <linux-mm@...ck.org>, Hugh Dickins <hughd@...gle.com>,
Dave Jones <davej@...hat.com>, Rik van Riel <riel@...hat.com>,
Ingo Molnar <mingo@...hat.com>,
Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
Sasha Levin <sasha.levin@...cle.com>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Mel Gorman <mgorman@...e.de>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [RFC PATCH 0/7] Replace _PAGE_NUMA with PAGE_NONE protections
Mel Gorman <mgorman@...e.de> writes:
> This is follow up from the "pipe/page fault oddness" thread.
>
> Automatic NUMA balancing depends on being able to protect PTEs to trap a
> fault and gather reference locality information. Very broadly speaking it
> would mark PTEs as not present and use another bit to distinguish between
> NUMA hinting faults and other types of faults. It was universally loved
> by everybody and caused no problems whatsoever. That last sentence might
> be a lie.
>
> This series is very heavily based on patches from Linus and Aneesh to
> replace the existing PTE/PMD NUMA helper functions with normal change
> protections. I did alter and add parts of it but I consider them relatively
> minor contributions. Note that the signed-offs here need addressing. I
> couldn't use "From" or Signed-off-by from the original authors as the
> patches had to be broken up and they were never signed off. I expect the
> two people involved will just stick their signed-off-by on it.
How about the additional change listed below for ppc64 ? One part of the
patch is to make sure that we don't hit the WARN_ON in set_pte and set_pmd
because we find the _PAGE_PRESENT bit set in case of numa fault. I
ended up relaxing the check there.
Second part of the change is to add a WARN_ON to make sure we are
not depending on DSISR_PROTFAULT for anything else. We ideally should not
get a DSISR_PROTFAULT for PROT_NONE or NUMA fault. hash_page_mm do check
whether the access is allowed by pte before inserting a pte into hash
page table. Hence we will never find a PROT_NONE or PROT_NONE_NUMA ptes
in hash page table. But it is good to run with VM_WARN_ON ?
I also added a similar change to handle CAPI.
This will also need an ack from Ben and Paul . (added them to Cc:)
With the below patch you can add
Acked-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
for the respective patches.
diff --git a/arch/powerpc/mm/copro_fault.c b/arch/powerpc/mm/copro_fault.c
index 5a236f082c78..2e208afb7f4c 100644
--- a/arch/powerpc/mm/copro_fault.c
+++ b/arch/powerpc/mm/copro_fault.c
@@ -64,10 +64,14 @@ int copro_handle_mm_fault(struct mm_struct *mm, unsigned long ea,
if (!(vma->vm_flags & VM_WRITE))
goto out_unlock;
} else {
- if (dsisr & DSISR_PROTFAULT)
- goto out_unlock;
if (!(vma->vm_flags & (VM_READ | VM_EXEC)))
goto out_unlock;
+ /*
+ * protfault should only happen due to us
+ * mapping a region readonly temporarily. PROT_NONE
+ * is also covered by the VMA check above.
+ */
+ VM_WARN_ON(dsisr & DSISR_PROTFAULT);
}
ret = 0;
diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
index 50074972d555..6df9483e316f 100644
--- a/arch/powerpc/mm/fault.c
+++ b/arch/powerpc/mm/fault.c
@@ -396,17 +396,6 @@ good_area:
#endif /* CONFIG_8xx */
if (is_exec) {
-#ifdef CONFIG_PPC_STD_MMU
- /* Protection fault on exec go straight to failure on
- * Hash based MMUs as they either don't support per-page
- * execute permission, or if they do, it's handled already
- * at the hash level. This test would probably have to
- * be removed if we change the way this works to make hash
- * processors use the same I/D cache coherency mechanism
- * as embedded.
- */
-#endif /* CONFIG_PPC_STD_MMU */
-
/*
* Allow execution from readable areas if the MMU does not
* provide separate controls over reading and executing.
@@ -421,6 +410,14 @@ good_area:
(cpu_has_feature(CPU_FTR_NOEXECUTE) ||
!(vma->vm_flags & (VM_READ | VM_WRITE))))
goto bad_area;
+#ifdef CONFIG_PPC_STD_MMU
+ /*
+ * protfault should only happen due to us
+ * mapping a region readonly temporarily. PROT_NONE
+ * is also covered by the VMA check above.
+ */
+ VM_WARN_ON(error_code & DSISR_PROTFAULT);
+#endif /* CONFIG_PPC_STD_MMU */
/* a write */
} else if (is_write) {
if (!(vma->vm_flags & VM_WRITE))
@@ -430,6 +427,7 @@ good_area:
} else {
if (!(vma->vm_flags & (VM_READ | VM_EXEC | VM_WRITE)))
goto bad_area;
+ VM_WARN_ON(error_code & DSISR_PROTFAULT);
}
/*
diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
index c90e602677c9..75b08098fcf5 100644
--- a/arch/powerpc/mm/pgtable.c
+++ b/arch/powerpc/mm/pgtable.c
@@ -172,9 +172,13 @@ static pte_t set_access_flags_filter(pte_t pte, struct vm_area_struct *vma,
void set_pte_at(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
pte_t pte)
{
-#ifdef CONFIG_DEBUG_VM
- WARN_ON(pte_val(*ptep) & _PAGE_PRESENT);
-#endif
+ /*
+ * When handling numa faults, we already have the pte marked
+ * _PAGE_PRESENT, but we can be sure that it is not in hpte.
+ * Hence we can use set_pte_at for them.
+ */
+ VM_WARN_ON((pte_val(*ptep) & (_PAGE_PRESENT | _PAGE_USER)) ==
+ (_PAGE_PRESENT | _PAGE_USER));
/* Note: mm->context.id might not yet have been assigned as
* this context might not have been activated yet when this
* is called.
diff --git a/arch/powerpc/mm/pgtable_64.c b/arch/powerpc/mm/pgtable_64.c
index c8d709ab489d..c721c5efb4df 100644
--- a/arch/powerpc/mm/pgtable_64.c
+++ b/arch/powerpc/mm/pgtable_64.c
@@ -710,7 +710,8 @@ void set_pmd_at(struct mm_struct *mm, unsigned long addr,
pmd_t *pmdp, pmd_t pmd)
{
#ifdef CONFIG_DEBUG_VM
- WARN_ON(pmd_val(*pmdp) & _PAGE_PRESENT);
+ WARN_ON((pmd_val(*pmdp) & (_PAGE_PRESENT | _PAGE_USER)) ==
+ (_PAGE_PRESENT | _PAGE_USER));
assert_spin_locked(&mm->page_table_lock);
WARN_ON(!pmd_trans_huge(pmd));
#endif
--
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