Re: [PATCH v2] mm: introduce arch_has_hw_nonleaf_pmd_young()
From: Juergen Gross
Date: Thu Nov 24 2022 - 09:30:16 EST
Hi,
On 24.11.22 15:08, Geert Uytterhoeven wrote:
Hi Jürgen,
On Wed, Nov 23, 2022 at 7:53 AM Juergen Gross <jgross@xxxxxxxx> wrote:
When running as a Xen PV guests commit eed9a328aa1a ("mm: x86: add
CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG") can cause a protection violation
in pmdp_test_and_clear_young():
BUG: unable to handle page fault for address: ffff8880083374d0
#PF: supervisor write access in kernel mode
#PF: error_code(0x0003) - permissions violation
PGD 3026067 P4D 3026067 PUD 3027067 PMD 7fee5067 PTE 8010000008337065
Oops: 0003 [#1] PREEMPT SMP NOPTI
CPU: 7 PID: 158 Comm: kswapd0 Not tainted 6.1.0-rc5-20221118-doflr+ #1
RIP: e030:pmdp_test_and_clear_young+0x25/0x40
This happens because the Xen hypervisor can't emulate direct writes to
page table entries other than PTEs.
This can easily be fixed by introducing arch_has_hw_nonleaf_pmd_young()
similar to arch_has_hw_pte_young() and test that instead of
CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG.
Fixes: eed9a328aa1a ("mm: x86: add CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG")
Reported-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
Acked-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Tested-by: Sander Eikelenboom <linux@xxxxxxxxxxxxxx>
---
V2:
- correct function name in commit message to match patch
Thanks for your patch, which is now commit 3f85e711d5af4fb4 ("mm:
introduce arch_has_hw_nonleaf_pmd_young()") in next-20221124.
noreply@xxxxxxxxxxxxxx reported a build failure for m68k/allmodconfig,
which I have bisected to this commit.
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4073,14 +4073,14 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
#endif
walk->mm_stats[MM_NONLEAF_TOTAL]++;
-#ifdef CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG
- if (get_cap(LRU_GEN_NONLEAF_YOUNG)) {
+ if (arch_has_hw_nonleaf_pmd_young() &&
+ get_cap(LRU_GEN_NONLEAF_YOUNG)) {
if (!pmd_young(val))
mm/vmscan.c:4102:30: error: implicit declaration of function
'pmd_young'; did you mean 'pte_young'?
[-Werror=implicit-function-declaration]
pmd_young() seems to be defined only on a handful of architectures.
What would be the preferred fix for that?
I could offer:
- use V1 of the patch
- add the #ifdefs again to this patch (which would be kind of weird)
- use the attached patch
Juergen
From 9f16c75dfbff994c01a003e4701f5bdd48cbfc3f Mon Sep 17 00:00:00 2001
From: Juergen Gross <jgross@xxxxxxxx>
Date: Thu, 24 Nov 2022 15:18:03 +0100
Subject: [PATCH] mm: add dummy pmd_young() for architectures not having it
In order to avoid #ifdeffery add a dummy pmd_young() implementation as
a fallback.
Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
arch/loongarch/include/asm/pgtable.h | 1 +
arch/mips/include/asm/pgtable.h | 1 +
arch/riscv/include/asm/pgtable.h | 1 +
arch/s390/include/asm/pgtable.h | 1 +
arch/sparc/include/asm/pgtable_64.h | 1 +
arch/x86/include/asm/pgtable.h | 1 +
include/linux/pgtable.h | 7 +++++++
7 files changed, 13 insertions(+)
diff --git a/arch/loongarch/include/asm/pgtable.h b/arch/loongarch/include/asm/pgtable.h
index 946704bee599..10e0bd9009e2 100644
--- a/arch/loongarch/include/asm/pgtable.h
+++ b/arch/loongarch/include/asm/pgtable.h
@@ -482,6 +482,7 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
return pmd;
}
+#define pmd_young pmd_young
static inline int pmd_young(pmd_t pmd)
{
return !!(pmd_val(pmd) & _PAGE_ACCESSED);
diff --git a/arch/mips/include/asm/pgtable.h b/arch/mips/include/asm/pgtable.h
index 6caec386ad2f..4678627673df 100644
--- a/arch/mips/include/asm/pgtable.h
+++ b/arch/mips/include/asm/pgtable.h
@@ -622,6 +622,7 @@ static inline pmd_t pmd_mkdirty(pmd_t pmd)
return pmd;
}
+#define pmd_young pmd_young
static inline int pmd_young(pmd_t pmd)
{
return !!(pmd_val(pmd) & _PAGE_ACCESSED);
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 7ec936910a96..92ec2d9d7273 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -600,6 +600,7 @@ static inline int pmd_dirty(pmd_t pmd)
return pte_dirty(pmd_pte(pmd));
}
+#define pmd_young pmd_young
static inline int pmd_young(pmd_t pmd)
{
return pte_young(pmd_pte(pmd));
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index f1cb9391190d..11e901286414 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -763,6 +763,7 @@ static inline int pmd_dirty(pmd_t pmd)
return (pmd_val(pmd) & _SEGMENT_ENTRY_DIRTY) != 0;
}
+#define pmd_young pmd_young
static inline int pmd_young(pmd_t pmd)
{
return (pmd_val(pmd) & _SEGMENT_ENTRY_YOUNG) != 0;
diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index a779418ceba9..3bc9736bddb1 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -693,6 +693,7 @@ static inline unsigned long pmd_dirty(pmd_t pmd)
return pte_dirty(pte);
}
+#define pmd_young pmd_young
static inline unsigned long pmd_young(pmd_t pmd)
{
pte_t pte = __pte(pmd_val(pmd));
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index 5059799bebe3..1d55af8d82b9 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -139,6 +139,7 @@ static inline int pmd_dirty(pmd_t pmd)
return pmd_flags(pmd) & _PAGE_DIRTY;
}
+#define pmd_young pmd_young
static inline int pmd_young(pmd_t pmd)
{
return pmd_flags(pmd) & _PAGE_ACCESSED;
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index a108b60a6962..6b0d59269b33 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -165,6 +165,13 @@ static inline pte_t *virt_to_kpte(unsigned long vaddr)
return pmd_none(*pmd) ? NULL : pte_offset_kernel(pmd, vaddr);
}
+#ifndef pmd_young
+static inline int pmd_young(pmd_t pmd)
+{
+ return 0;
+}
+#endif
+
#ifndef __HAVE_ARCH_PTEP_SET_ACCESS_FLAGS
extern int ptep_set_access_flags(struct vm_area_struct *vma,
unsigned long address, pte_t *ptep,
--
2.35.3
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