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Date: Mon, 30 Aug 2021 11:52:19 +0000
From: "Boehme, Markus" <markubo@...zon.de>
To: "sj38.park@...il.com" <sj38.park@...il.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
CC: "Boehme, Markus" <markubo@...zon.de>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"david@...hat.com" <david@...hat.com>,
"Park, Seongjae" <sjpark@...zon.de>
Subject: Re: [PATCH] mm/damon/vaddr: Safely walk page table
On Fri, 2021-08-27 at 15:04 +0000, SeongJae Park wrote:
>
> From: SeongJae Park <sjpark@...zon.de>
>
> Commit d7f647622761 ("mm/damon: implement primitives for the virtual
> memory address spaces") of linux-mm[1] tries to find PTE or PMD for
> arbitrary virtual address using 'follow_invalidate_pte()' without proper
> locking[2]. This commit fixes the issue by using another page table
> walk function for more general use case under proper locking.
>
> [1] https://github.com/hnaz/linux-mm/commit/d7f647622761
> [2] https://lore.kernel.org/linux-mm/3b094493-9c1e-6024-bfd5-7eca66399b7e@redhat.com
>
> Fixes: d7f647622761 ("mm/damon: implement primitives for the virtual memory address spaces")
> Reported-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: SeongJae Park <sjpark@...zon.de>
> ---
> mm/damon/vaddr.c | 81 +++++++++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 74 insertions(+), 7 deletions(-)
>
> diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> index 230db7413278..b3677f2ef54b 100644
> --- a/mm/damon/vaddr.c
> +++ b/mm/damon/vaddr.c
> @@ -8,10 +8,12 @@
> #define pr_fmt(fmt) "damon-va: " fmt
>
> #include <linux/damon.h>
> +#include <linux/hugetlb.h>
> #include <linux/mm.h>
> #include <linux/mmu_notifier.h>
> #include <linux/highmem.h>
> #include <linux/page_idle.h>
> +#include <linux/pagewalk.h>
> #include <linux/random.h>
> #include <linux/sched/mm.h>
> #include <linux/slab.h>
> @@ -446,14 +448,69 @@ static void damon_pmdp_mkold(pmd_t *pmd, struct mm_struct *mm,
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
> }
>
> +struct damon_walk_private {
> + pmd_t *pmd;
> + pte_t *pte;
> + spinlock_t *ptl;
> +};
> +
> +static int damon_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,
> + struct mm_walk *walk)
> +{
> + struct damon_walk_private *priv = walk->private;
> +
> + if (pmd_huge(*pmd)) {
> + priv->ptl = pmd_lock(walk->mm, pmd);
> + if (pmd_huge(*pmd)) {
> + priv->pmd = pmd;
> + return 0;
> + }
> + spin_unlock(priv->ptl);
> + }
> +
> + if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
> + return -EINVAL;
> + priv->pte = pte_offset_map_lock(walk->mm, pmd, addr, &priv->ptl);
> + if (!pte_present(*priv->pte)) {
> + pte_unmap_unlock(priv->pte, priv->ptl);
> + priv->pte = NULL;
> + return -EINVAL;
> + }
> + return 0;
> +}
> +
> +static struct mm_walk_ops damon_walk_ops = {
> + .pmd_entry = damon_pmd_entry,
> +};
> +
> +int damon_follow_pte_pmd(struct mm_struct *mm, unsigned long addr,
> + struct damon_walk_private *private)
> +{
> + int rc;
> +
> + private->pte = NULL;
> + private->pmd = NULL;
> + rc = walk_page_range(mm, addr, addr + 1, &damon_walk_ops, private);
> + if (!rc && !private->pte && !private->pmd)
> + return -EINVAL;
> + return rc;
> +}
> +
> static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
> {
> - pte_t *pte = NULL;
> - pmd_t *pmd = NULL;
> + struct damon_walk_private walk_result;
> + pte_t *pte;
> + pmd_t *pmd;
> spinlock_t *ptl;
>
> - if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))
> + mmap_write_lock(mm);
> + if (damon_follow_pte_pmd(mm, addr, &walk_result)) {
> + mmap_write_unlock(mm);
> return;
> + }
> + pte = walk_result.pte;
> + pmd = walk_result.pmd;
> + ptl = walk_result.ptl;
>
> if (pte) {
> damon_ptep_mkold(pte, mm, addr);
> @@ -462,6 +519,7 @@ static void damon_va_mkold(struct mm_struct *mm, unsigned long addr)
> damon_pmdp_mkold(pmd, mm, addr);
> spin_unlock(ptl);
> }
> + mmap_write_unlock(mm);
> }
>
> /*
> @@ -495,14 +553,21 @@ void damon_va_prepare_access_checks(struct damon_ctx *ctx)
> static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
> unsigned long *page_sz)
> {
> - pte_t *pte = NULL;
> - pmd_t *pmd = NULL;
> + struct damon_walk_private walk_result;
> + pte_t *pte;
> + pmd_t *pmd;
> spinlock_t *ptl;
> struct page *page;
> bool young = false;
>
> - if (follow_invalidate_pte(mm, addr, NULL, &pte, &pmd, &ptl))
> + mmap_write_lock(mm);
> + if (damon_follow_pte_pmd(mm, addr, &walk_result)) {
> + mmap_write_unlock(mm);
> return false;
> + }
> + pte = walk_result.pte;
> + pmd = walk_result.pmd;
> + ptl = walk_result.ptl;
>
> *page_sz = PAGE_SIZE;
> if (pte) {
> @@ -513,7 +578,7 @@ static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
> if (page)
> put_page(page);
> pte_unmap_unlock(pte, ptl);
> - return young;
> + goto out;
> }
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> @@ -528,6 +593,8 @@ static bool damon_va_young(struct mm_struct *mm, unsigned long addr,
> *page_sz = ((1UL) << HPAGE_PMD_SHIFT);
> #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> +out:
> + mmap_write_unlock(mm);
> return young;
> }
>
> --
> 2.17.1
>
Reviewed-by: Markus Boehme <markubo@...zon.de>
Amazon Development Center Germany GmbH
Krausenstr. 38
10117 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 149173 B
Sitz: Berlin
Ust-ID: DE 289 237 879
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