[PATCH v4 0/5] Fix some cache flush bugs

[PATCH v4 0/5] Fix some cache flush bugs

[Muchun Song]

This series focus on fixing cache maintenance.

v4:
  - Replace folio_copy() with copy_user_huge_page().
  - Update commit message for patch 2.

v3:
  - Collect Reviewed-by tag from Zi Yan.
  - Fix hugetlb cache maintenance.

v2:
  - Collect Reviewed-by tag from Zi Yan.
  - Using a for loop instead of the folio variant for backportability.

Muchun Song (5):
  mm: thp: fix wrong cache flush in remove_migration_pmd()
  mm: fix missing cache flush for all tail pages of compound page
  mm: hugetlb: fix missing cache flush in copy_huge_page_from_user()
  mm: hugetlb: fix missing cache flush in hugetlb_mcopy_atomic_pte()
  mm: replace multiple dcache flush with flush_dcache_folio()

 mm/huge_memory.c | 3 ++-
 mm/hugetlb.c     | 3 ++-
 mm/memory.c      | 2 ++
 mm/migrate.c     | 3 +--
 4 files changed, 7 insertions(+), 4 deletions(-)

-- 
2.11.0

[PATCH v4 1/5] mm: thp: fix wrong cache flush in remove_migration_pmd()

[Muchun Song]

The flush_cache_range() is supposed to be justified only if the page
is already placed in process page table, and that is done right after
flush_cache_range(). So using this interface is wrong. And there is
no need to invalite cache since it was non-present before in
remove_migration_pmd(). So just to remove it.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
 mm/huge_memory.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f58524394dc1..45ede45b11f5 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3207,7 +3207,6 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	if (pmd_swp_uffd_wp(*pvmw->pmd))
 		pmde = pmd_wrprotect(pmd_mkuffd_wp(pmde));
 
-	flush_cache_range(vma, mmun_start, mmun_start + HPAGE_PMD_SIZE);
 	if (PageAnon(new))
 		page_add_anon_rmap(new, vma, mmun_start, true);
 	else
@@ -3215,6 +3214,8 @@ void remove_migration_pmd(struct page_vma_mapped_walk *pvmw, struct page *new)
 	set_pmd_at(mm, mmun_start, pvmw->pmd, pmde);
 	if ((vma->vm_flags & VM_LOCKED) && !PageDoubleMap(new))
 		mlock_vma_page(new);
+
+	/* No need to invalidate - it was non-present before */
 	update_mmu_cache_pmd(vma, address, pvmw->pmd);
 }
 #endif
-- 
2.11.0

[PATCH v4 2/5] mm: fix missing cache flush for all tail pages of compound page

[Muchun Song]

The D-cache maintenance inside move_to_new_page() only consider one page,
there is still D-cache maintenance issue for tail pages of compound page
(e.g. THP or HugeTLB).  THP migration is only enabled on x86_64, ARM64
and powerpc, while powerpc and arm64 need to maintain the consistency
between I-Cache and D-Cache, which depends on flush_dcache_page() to
maintain the consistency between I-Cache and D-Cache.  But there is no
issues on arm64 and powerpc since they already considers the compound
page cache flushing in their icache flush function.  HugeTLB migration
is enabled on arm, arm64, mips, parisc, powerpc, riscv, s390 and sh, while
arm has handled the compound page cache flush in flush_dcache_page(), but
most others do not.  In theory, the issue exists on many architectures.
Fix this by not using flush_dcache_folio() since it is not backportable.

Fixes: 290408d4a250 ("hugetlb: hugepage migration core")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
---
 mm/migrate.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c9296d63878d..c418e8d92b9c 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -933,9 +933,12 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 		if (!PageMappingFlags(page))
 			page->mapping = NULL;
 
-		if (likely(!is_zone_device_page(newpage)))
-			flush_dcache_page(newpage);
+		if (likely(!is_zone_device_page(newpage))) {
+			int i, nr = compound_nr(newpage);
 
+			for (i = 0; i < nr; i++)
+				flush_dcache_page(newpage + i);
+		}
 	}
 out:
 	return rc;
-- 
2.11.0

[PATCH v4 3/5] mm: hugetlb: fix missing cache flush in copy_huge_page_from_user()

[Muchun Song]

The userfaultfd calls copy_huge_page_from_user() which does not do
any cache flushing for the target page.  Then the target page will
be mapped to the user space with a different address (user address),
which might have an alias issue with the kernel address used to copy
the data from the user to.  Fix this issue by flushing dcache in
copy_huge_page_from_user().

Fixes: fa4d75c1de13 ("userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/memory.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c
index e8ce066be5f2..eb027da68aa7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5405,6 +5405,8 @@ long copy_huge_page_from_user(struct page *dst_page,
 		if (rc)
 			break;
 
+		flush_dcache_page(subpage);
+
 		cond_resched();
 	}
 	return ret_val;
-- 
2.11.0

Re: [PATCH v4 3/5] mm: hugetlb: fix missing cache flush in copy_huge_page_from_user()

[Mike Kravetz]

On 2/7/22 23:36, Muchun Song wrote:
> The userfaultfd calls copy_huge_page_from_user() which does not do
> any cache flushing for the target page.  Then the target page will
> be mapped to the user space with a different address (user address),
> which might have an alias issue with the kernel address used to copy
> the data from the user to.  Fix this issue by flushing dcache in
> copy_huge_page_from_user().

Quick question.

Should this also be done for the non-hugetlb case?  Take a look at the
routines __mcopy_atomic() and mcopy_atomic_pte().  Or, is that somehow
handled?

For this change,
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz

> 
> Fixes: fa4d75c1de13 ("userfaultfd: hugetlbfs: add copy_huge_page_from_user for hugetlb userfaultfd support")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/memory.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/mm/memory.c b/mm/memory.c
> index e8ce066be5f2..eb027da68aa7 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5405,6 +5405,8 @@ long copy_huge_page_from_user(struct page *dst_page,
>  		if (rc)
>  			break;
>  
> +		flush_dcache_page(subpage);
> +
>  		cond_resched();
>  	}
>  	return ret_val;

Re: [PATCH v4 3/5] mm: hugetlb: fix missing cache flush in copy_huge_page_from_user()

[Muchun Song]

On Thu, Feb 10, 2022 at 3:07 AM Mike Kravetz <mike.kravetz@oracle.com> wrote:
>
> On 2/7/22 23:36, Muchun Song wrote:
> > The userfaultfd calls copy_huge_page_from_user() which does not do
> > any cache flushing for the target page.  Then the target page will
> > be mapped to the user space with a different address (user address),
> > which might have an alias issue with the kernel address used to copy
> > the data from the user to.  Fix this issue by flushing dcache in
> > copy_huge_page_from_user().
>
> Quick question.
>
> Should this also be done for the non-hugetlb case?  Take a look at the
> routines __mcopy_atomic() and mcopy_atomic_pte().  Or, is that somehow
> handled?

Actually, you are right. __mcopy_atomic() and mcopy_atomic_pte()
should also be fixed.  And shmem_mfill_atomic_pte() also should
be fixed. I'll fix those places in the next version. Thanks.

>
> For this change,
> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

Thanks Mike.

[PATCH v4 4/5] mm: hugetlb: fix missing cache flush in hugetlb_mcopy_atomic_pte()

[Muchun Song]

folio_copy() will copy the data from one page to the target page, then
the target page will be mapped to the user space address, which might
have an alias issue with the kernel address used to copy the data from
the page to.  There are 2 ways to fix this issue.

 1) insert flush_dcache_page() after folio_copy().
 2) replace folio_copy() with copy_user_huge_page() which already
    considers the cache maintenance.

We chose 2) way to fix the issue since architectures can optimize this
situation.

Fixes: 8cc5fcbb5be8 ("mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/hugetlb.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a1baa198519a..eba7681d15d0 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5818,7 +5818,8 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
 			*pagep = NULL;
 			goto out;
 		}
-		folio_copy(page_folio(page), page_folio(*pagep));
+		copy_user_huge_page(page, *pagep, dst_addr, dst_vma,
+				    pages_per_huge_page(h));
 		put_page(*pagep);
 		*pagep = NULL;
 	}
-- 
2.11.0

Re: [PATCH v4 4/5] mm: hugetlb: fix missing cache flush in hugetlb_mcopy_atomic_pte()

[Mike Kravetz]

On 2/7/22 23:36, Muchun Song wrote:
> folio_copy() will copy the data from one page to the target page, then
> the target page will be mapped to the user space address, which might
> have an alias issue with the kernel address used to copy the data from
> the page to.  There are 2 ways to fix this issue.
> 
>  1) insert flush_dcache_page() after folio_copy().
>  2) replace folio_copy() with copy_user_huge_page() which already
>     considers the cache maintenance.
> 
> We chose 2) way to fix the issue since architectures can optimize this
> situation.
> 
> Fixes: 8cc5fcbb5be8 ("mm, hugetlb: fix racy resv_huge_pages underflow on UFFDIO_COPY")
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/hugetlb.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Thanks!  This will also make backports easier.

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>

-- 
Mike Kravetz

[PATCH v4 5/5] mm: replace multiple dcache flush with flush_dcache_folio()

[Muchun Song]

Simplify the code by using flush_dcache_folio().

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 mm/migrate.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c418e8d92b9c..daf2b3508670 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -933,12 +933,8 @@ static int move_to_new_page(struct page *newpage, struct page *page,
 		if (!PageMappingFlags(page))
 			page->mapping = NULL;
 
-		if (likely(!is_zone_device_page(newpage))) {
-			int i, nr = compound_nr(newpage);
-
-			for (i = 0; i < nr; i++)
-				flush_dcache_page(newpage + i);
-		}
+		if (likely(!is_zone_device_page(newpage)))
+			flush_dcache_folio(page_folio(newpage));
 	}
 out:
 	return rc;
-- 
2.11.0

Re: [PATCH v4 5/5] mm: replace multiple dcache flush with flush_dcache_folio()

[Mike Kravetz]

On 2/7/22 23:36, Muchun Song wrote:
> Simplify the code by using flush_dcache_folio().
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---
>  mm/migrate.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)

Thanks,

Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
-- 
Mike Kravetz

> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index c418e8d92b9c..daf2b3508670 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -933,12 +933,8 @@ static int move_to_new_page(struct page *newpage, struct page *page,
>  		if (!PageMappingFlags(page))
>  			page->mapping = NULL;
>  
> -		if (likely(!is_zone_device_page(newpage))) {
> -			int i, nr = compound_nr(newpage);
> -
> -			for (i = 0; i < nr; i++)
> -				flush_dcache_page(newpage + i);
> -		}
> +		if (likely(!is_zone_device_page(newpage)))
> +			flush_dcache_folio(page_folio(newpage));
>  	}
>  out:
>  	return rc;