Re: [PATCH v3 12/15] mm/memory: pass PTE to copy_present_pte()

David Hildenbrand
2024-02-14T22:40:27Z

On 29.01.24 13:46, David Hildenbrand wrote:
> We already read it, let's just forward it.
>
> This patch is based on work by Ryan Roberts.
>
> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> mm/memory.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/mm/memory.c b/mm/memory.c
> index a3bdb25f4c8d..41b24da5be38 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -959,10 +959,9 @@ static inline void __copy_present_pte(struct vm_area_struct *dst_vma,
> */
> static inline int
> copy_present_pte(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
> - pte_t *dst_pte, pte_t *src_pte, unsigned long addr, int *rss,
> - struct folio **prealloc)
> + pte_t *dst_pte, pte_t *src_pte, pte_t pte, unsigned long addr,
> + int *rss, struct folio **prealloc)
> {
> - pte_t pte = ptep_get(src_pte);
> struct page *page;
> struct folio *folio;
>
> @@ -1103,7 +1102,7 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
> }
> /* copy_present_pte() will clear `*prealloc' if consumed */
> ret = copy_present_pte(dst_vma, src_vma, dst_pte, src_pte,
> - addr, rss, &prealloc);
> + ptent, addr, rss, &prealloc);
> /*
> * If we need a pre-allocated page for this pte, drop the
> * locks, allocate, and try again.

The following fixup for that device-exclusive thingy on top (fixing a hmm
selftest I just discovered to be broken).

From 8f9e44f25087dc71890b8d9bd680375691232e85 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@redhat.com>
Date: Wed, 14 Feb 2024 23:09:29 +0100
Subject: [PATCH] fixup: mm/memory: pass PTE to copy_present_pte()

For device-exclusive nonswp entries (is_device_exclusive_entry()),
copy_nonpresent_pte() can turn the PTEs into actual present PTEs while
holding the page table lock.

We hae to re-read the PTE after that operation, such that we won't be
working on the stale non-present PTE, assuming it would be present.

This fixes the hmm "exclusive_cow" selftest.

./run_vmtests.sh -t hmm
# # RUN hmm.hmm_device_private.exclusive_cow ...
# # OK hmm.hmm_device_private.exclusive_cow
# ok 23 hmm.hmm_device_private.exclusive_cow

Signed-off-by: David Hildenbrand <david@redhat.com>
---
mm/memory.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index 3b8e56eb08a3..29a75f38df7c 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1208,6 +1208,8 @@ copy_pte_range(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma,
progress += 8;
continue;
}
+ ptent = ptep_get(src_pte);
+ VM_WARN_ON_ONCE(!pte_present(ptent));

/*
* Device exclusive entry restored, continue by copying
--
2.43.0

--
Cheers,

David / dhildenb