[PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[Lorenzo Stoakes]

The only instances of get_user_pages_remote() invocations which used the
vmas parameter were for a single page which can instead simply look up the
VMA directly. In particular:-

- __update_ref_ctr() looked up the VMA but did nothing with it so we simply
  remove it.

- __access_remote_vm() was already using vma_lookup() when the original
  lookup failed so by doing the lookup directly this also de-duplicates the
  code.

We are able to perform these VMA operations as we already hold the
mmap_lock in order to be able to call get_user_pages_remote().

As part of this work we add get_user_page_vma_remote() which abstracts the
VMA lookup, error handling and decrementing the page reference count should
the VMA lookup fail.

This forms part of a broader set of patches intended to eliminate the vmas
parameter altogether.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> (for arm64)
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Janosch Frank <frankja@linux.ibm.com> (for s390)
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
 arch/arm64/kernel/mte.c   | 17 +++++++++--------
 arch/s390/kvm/interrupt.c |  2 +-
 fs/exec.c                 |  2 +-
 include/linux/mm.h        | 34 +++++++++++++++++++++++++++++++---
 kernel/events/uprobes.c   | 13 +++++--------
 mm/gup.c                  | 12 ++++--------
 mm/memory.c               | 14 +++++++-------
 mm/rmap.c                 |  2 +-
 security/tomoyo/domain.c  |  2 +-
 virt/kvm/async_pf.c       |  3 +--
 10 files changed, 61 insertions(+), 40 deletions(-)

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index f5bcb0dc6267..cc793c246653 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -419,10 +419,9 @@ long get_mte_ctrl(struct task_struct *task)
 static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
 				struct iovec *kiov, unsigned int gup_flags)
 {
-	struct vm_area_struct *vma;
 	void __user *buf = kiov->iov_base;
 	size_t len = kiov->iov_len;
-	int ret;
+	int err = 0;
 	int write = gup_flags & FOLL_WRITE;
 
 	if (!access_ok(buf, len))
@@ -432,14 +431,16 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
 		return -EIO;
 
 	while (len) {
+		struct vm_area_struct *vma;
 		unsigned long tags, offset;
 		void *maddr;
-		struct page *page = NULL;
+		struct page *page = get_user_page_vma_remote(mm, addr,
+							     gup_flags, &vma);
 
-		ret = get_user_pages_remote(mm, addr, 1, gup_flags, &page,
-					    &vma, NULL);
-		if (ret <= 0)
+		if (IS_ERR_OR_NULL(page)) {
+			err = page == NULL ? -EIO : PTR_ERR(page);
 			break;
+		}
 
 		/*
 		 * Only copy tags if the page has been mapped as PROT_MTE
@@ -449,7 +450,7 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
 		 * was never mapped with PROT_MTE.
 		 */
 		if (!(vma->vm_flags & VM_MTE)) {
-			ret = -EOPNOTSUPP;
+			err = -EOPNOTSUPP;
 			put_page(page);
 			break;
 		}
@@ -482,7 +483,7 @@ static int __access_remote_tags(struct mm_struct *mm, unsigned long addr,
 	kiov->iov_len = buf - kiov->iov_base;
 	if (!kiov->iov_len) {
 		/* check for error accessing the tracee's address space */
-		if (ret <= 0)
+		if (err)
 			return -EIO;
 		else
 			return -EFAULT;
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index da6dac36e959..9bd0a873f3b1 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -2777,7 +2777,7 @@ static struct page *get_map_page(struct kvm *kvm, u64 uaddr)
 
 	mmap_read_lock(kvm->mm);
 	get_user_pages_remote(kvm->mm, uaddr, 1, FOLL_WRITE,
-			      &page, NULL, NULL);
+			      &page, NULL);
 	mmap_read_unlock(kvm->mm);
 	return page;
 }
diff --git a/fs/exec.c b/fs/exec.c
index a466e797c8e2..25c65b64544b 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -220,7 +220,7 @@ static struct page *get_arg_page(struct linux_binprm *bprm, unsigned long pos,
 	 */
 	mmap_read_lock(bprm->mm);
 	ret = get_user_pages_remote(bprm->mm, pos, 1, gup_flags,
-			&page, NULL, NULL);
+			&page, NULL);
 	mmap_read_unlock(bprm->mm);
 	if (ret <= 0)
 		return NULL;
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 8ea82e9e7719..679b41ef7a6d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2366,6 +2366,9 @@ static inline void unmap_shared_mapping_range(struct address_space *mapping,
 	unmap_mapping_range(mapping, holebegin, holelen, 0);
 }
 
+static inline struct vm_area_struct *vma_lookup(struct mm_struct *mm,
+						unsigned long addr);
+
 extern int access_process_vm(struct task_struct *tsk, unsigned long addr,
 		void *buf, int len, unsigned int gup_flags);
 extern int access_remote_vm(struct mm_struct *mm, unsigned long addr,
@@ -2374,13 +2377,38 @@ extern int __access_remote_vm(struct mm_struct *mm, unsigned long addr,
 			      void *buf, int len, unsigned int gup_flags);
 
 long get_user_pages_remote(struct mm_struct *mm,
-			    unsigned long start, unsigned long nr_pages,
-			    unsigned int gup_flags, struct page **pages,
-			    struct vm_area_struct **vmas, int *locked);
+			   unsigned long start, unsigned long nr_pages,
+			   unsigned int gup_flags, struct page **pages,
+			   int *locked);
 long pin_user_pages_remote(struct mm_struct *mm,
 			   unsigned long start, unsigned long nr_pages,
 			   unsigned int gup_flags, struct page **pages,
 			   int *locked);
+
+static inline struct page *get_user_page_vma_remote(struct mm_struct *mm,
+						    unsigned long addr,
+						    int gup_flags,
+						    struct vm_area_struct **vmap)
+{
+	struct page *page;
+	struct vm_area_struct *vma;
+	int got = get_user_pages_remote(mm, addr, 1, gup_flags, &page, NULL);
+
+	if (got < 0)
+		return ERR_PTR(got);
+	if (got == 0)
+		return NULL;
+
+	vma = vma_lookup(mm, addr);
+	if (WARN_ON_ONCE(!vma)) {
+		put_page(page);
+		return ERR_PTR(-EINVAL);
+	}
+
+	*vmap = vma;
+	return page;
+}
+
 long get_user_pages(unsigned long start, unsigned long nr_pages,
 		    unsigned int gup_flags, struct page **pages);
 long pin_user_pages(unsigned long start, unsigned long nr_pages,
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 59887c69d54c..cac3aef7c6f7 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -365,7 +365,6 @@ __update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
 {
 	void *kaddr;
 	struct page *page;
-	struct vm_area_struct *vma;
 	int ret;
 	short *ptr;
 
@@ -373,7 +372,7 @@ __update_ref_ctr(struct mm_struct *mm, unsigned long vaddr, short d)
 		return -EINVAL;
 
 	ret = get_user_pages_remote(mm, vaddr, 1,
-			FOLL_WRITE, &page, &vma, NULL);
+				    FOLL_WRITE, &page, NULL);
 	if (unlikely(ret <= 0)) {
 		/*
 		 * We are asking for 1 page. If get_user_pages_remote() fails,
@@ -474,10 +473,9 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
 	if (is_register)
 		gup_flags |= FOLL_SPLIT_PMD;
 	/* Read the page with vaddr into memory */
-	ret = get_user_pages_remote(mm, vaddr, 1, gup_flags,
-				    &old_page, &vma, NULL);
-	if (ret <= 0)
-		return ret;
+	old_page = get_user_page_vma_remote(mm, vaddr, gup_flags, &vma);
+	if (IS_ERR_OR_NULL(old_page))
+		return PTR_ERR(old_page);
 
 	ret = verify_opcode(old_page, vaddr, &opcode);
 	if (ret <= 0)
@@ -2027,8 +2025,7 @@ static int is_trap_at_addr(struct mm_struct *mm, unsigned long vaddr)
 	 * but we treat this as a 'remote' access since it is
 	 * essentially a kernel access to the memory.
 	 */
-	result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page,
-			NULL, NULL);
+	result = get_user_pages_remote(mm, vaddr, 1, FOLL_FORCE, &page, NULL);
 	if (result < 0)
 		return result;
 
diff --git a/mm/gup.c b/mm/gup.c
index ce78a5186dbb..1493cc8dd526 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2208,8 +2208,6 @@ static bool is_valid_gup_args(struct page **pages, struct vm_area_struct **vmas,
  * @pages:	array that receives pointers to the pages pinned.
  *		Should be at least nr_pages long. Or NULL, if caller
  *		only intends to ensure the pages are faulted in.
- * @vmas:	array of pointers to vmas corresponding to each page.
- *		Or NULL if the caller does not require them.
  * @locked:	pointer to lock flag indicating whether lock is held and
  *		subsequently whether VM_FAULT_RETRY functionality can be
  *		utilised. Lock must initially be held.
@@ -2224,8 +2222,6 @@ static bool is_valid_gup_args(struct page **pages, struct vm_area_struct **vmas,
  *
  * The caller is responsible for releasing returned @pages, via put_page().
  *
- * @vmas are valid only as long as mmap_lock is held.
- *
  * Must be called with mmap_lock held for read or write.
  *
  * get_user_pages_remote walks a process's page tables and takes a reference
@@ -2262,15 +2258,15 @@ static bool is_valid_gup_args(struct page **pages, struct vm_area_struct **vmas,
 long get_user_pages_remote(struct mm_struct *mm,
 		unsigned long start, unsigned long nr_pages,
 		unsigned int gup_flags, struct page **pages,
-		struct vm_area_struct **vmas, int *locked)
+		int *locked)
 {
 	int local_locked = 1;
 
-	if (!is_valid_gup_args(pages, vmas, locked, &gup_flags,
+	if (!is_valid_gup_args(pages, NULL, locked, &gup_flags,
 			       FOLL_TOUCH | FOLL_REMOTE))
 		return -EINVAL;
 
-	return __get_user_pages_locked(mm, start, nr_pages, pages, vmas,
+	return __get_user_pages_locked(mm, start, nr_pages, pages, NULL,
 				       locked ? locked : &local_locked,
 				       gup_flags);
 }
@@ -2280,7 +2276,7 @@ EXPORT_SYMBOL(get_user_pages_remote);
 long get_user_pages_remote(struct mm_struct *mm,
 			   unsigned long start, unsigned long nr_pages,
 			   unsigned int gup_flags, struct page **pages,
-			   struct vm_area_struct **vmas, int *locked)
+			   int *locked)
 {
 	return 0;
 }
diff --git a/mm/memory.c b/mm/memory.c
index 146bb94764f8..63632a5eafc1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5590,7 +5590,6 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
 int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 		       int len, unsigned int gup_flags)
 {
-	struct vm_area_struct *vma;
 	void *old_buf = buf;
 	int write = gup_flags & FOLL_WRITE;
 
@@ -5599,13 +5598,15 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 
 	/* ignore errors, just check how much was successfully transferred */
 	while (len) {
-		int bytes, ret, offset;
+		int bytes, offset;
 		void *maddr;
-		struct page *page = NULL;
+		struct vm_area_struct *vma;
+		struct page *page = get_user_page_vma_remote(mm, addr,
+							     gup_flags, &vma);
+
+		if (IS_ERR_OR_NULL(page)) {
+			int ret = 0;
 
-		ret = get_user_pages_remote(mm, addr, 1,
-				gup_flags, &page, &vma, NULL);
-		if (ret <= 0) {
 #ifndef CONFIG_HAVE_IOREMAP_PROT
 			break;
 #else
@@ -5613,7 +5614,6 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
 			 * we can access using slightly different code.
 			 */
-			vma = vma_lookup(mm, addr);
 			if (!vma)
 				break;
 			if (vma->vm_ops && vma->vm_ops->access)
diff --git a/mm/rmap.c b/mm/rmap.c
index b42fc0389c24..ae127f60a4fb 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2328,7 +2328,7 @@ int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
 
 	npages = get_user_pages_remote(mm, start, npages,
 				       FOLL_GET | FOLL_WRITE | FOLL_SPLIT_PMD,
-				       pages, NULL, NULL);
+				       pages, NULL);
 	if (npages < 0)
 		return npages;
 
diff --git a/security/tomoyo/domain.c b/security/tomoyo/domain.c
index 31af29f669d2..ac20c0bdff9d 100644
--- a/security/tomoyo/domain.c
+++ b/security/tomoyo/domain.c
@@ -916,7 +916,7 @@ bool tomoyo_dump_page(struct linux_binprm *bprm, unsigned long pos,
 	 */
 	mmap_read_lock(bprm->mm);
 	ret = get_user_pages_remote(bprm->mm, pos, 1,
-				    FOLL_FORCE, &page, NULL, NULL);
+				    FOLL_FORCE, &page, NULL);
 	mmap_read_unlock(bprm->mm);
 	if (ret <= 0)
 		return false;
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index 9bfe1d6f6529..e033c79d528e 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -61,8 +61,7 @@ static void async_pf_execute(struct work_struct *work)
 	 * access remotely.
 	 */
 	mmap_read_lock(mm);
-	get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, NULL,
-			&locked);
+	get_user_pages_remote(mm, addr, 1, FOLL_WRITE, NULL, &locked);
 	if (locked)
 		mmap_read_unlock(mm);
 
-- 
2.40.1

Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[Christoph Hellwig]

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[Anders Roxell]

On 2023-05-14 22:26, Lorenzo Stoakes wrote:
> The only instances of get_user_pages_remote() invocations which used the
> vmas parameter were for a single page which can instead simply look up the
> VMA directly. In particular:-
> 
> - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
>   remove it.
> 
> - __access_remote_vm() was already using vma_lookup() when the original
>   lookup failed so by doing the lookup directly this also de-duplicates the
>   code.
> 
> We are able to perform these VMA operations as we already hold the
> mmap_lock in order to be able to call get_user_pages_remote().
> 
> As part of this work we add get_user_page_vma_remote() which abstracts the
> VMA lookup, error handling and decrementing the page reference count should
> the VMA lookup fail.
> 
> This forms part of a broader set of patches intended to eliminate the vmas
> parameter altogether.
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> (for arm64)
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Janosch Frank <frankja@linux.ibm.com> (for s390)
> Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
> ---
>  arch/arm64/kernel/mte.c   | 17 +++++++++--------
>  arch/s390/kvm/interrupt.c |  2 +-
>  fs/exec.c                 |  2 +-
>  include/linux/mm.h        | 34 +++++++++++++++++++++++++++++++---
>  kernel/events/uprobes.c   | 13 +++++--------
>  mm/gup.c                  | 12 ++++--------
>  mm/memory.c               | 14 +++++++-------
>  mm/rmap.c                 |  2 +-
>  security/tomoyo/domain.c  |  2 +-
>  virt/kvm/async_pf.c       |  3 +--
>  10 files changed, 61 insertions(+), 40 deletions(-)
> 

[...]

> diff --git a/mm/memory.c b/mm/memory.c
> index 146bb94764f8..63632a5eafc1 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -5590,7 +5590,6 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
>  int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
>  		       int len, unsigned int gup_flags)
>  {
> -	struct vm_area_struct *vma;
>  	void *old_buf = buf;
>  	int write = gup_flags & FOLL_WRITE;
>  
> @@ -5599,13 +5598,15 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
>  
>  	/* ignore errors, just check how much was successfully transferred */
>  	while (len) {
> -		int bytes, ret, offset;
> +		int bytes, offset;
>  		void *maddr;
> -		struct page *page = NULL;
> +		struct vm_area_struct *vma;
> +		struct page *page = get_user_page_vma_remote(mm, addr,
> +							     gup_flags, &vma);
> +
> +		if (IS_ERR_OR_NULL(page)) {
> +			int ret = 0;

I see the warning below when building without CONFIG_HAVE_IOREMAP_PROT set.

make --silent --keep-going --jobs=32 \
O=/home/anders/.cache/tuxmake/builds/1244/build ARCH=arm \
CROSS_COMPILE=arm-linux-gnueabihf- /home/anders/src/kernel/next/mm/memory.c: In function '__access_remote_vm':
/home/anders/src/kernel/next/mm/memory.c:5608:29: warning: unused variable 'ret' [-Wunused-variable]
 5608 |                         int ret = 0;
      |                             ^~~


>  
> -		ret = get_user_pages_remote(mm, addr, 1,
> -				gup_flags, &page, &vma, NULL);
> -		if (ret <= 0) {
>  #ifndef CONFIG_HAVE_IOREMAP_PROT
>  			break;
>  #else
> @@ -5613,7 +5614,6 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
>  			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
>  			 * we can access using slightly different code.
>  			 */
> -			vma = vma_lookup(mm, addr);
>  			if (!vma)
>  				break;
>  			if (vma->vm_ops && vma->vm_ops->access)

Cheers,
Anders

Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[Lorenzo Stoakes]

On Tue, May 16, 2023 at 11:49:19AM +0200, Anders Roxell wrote:
> On 2023-05-14 22:26, Lorenzo Stoakes wrote:
> > The only instances of get_user_pages_remote() invocations which used the
> > vmas parameter were for a single page which can instead simply look up the
> > VMA directly. In particular:-
> >
> > - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
> >   remove it.
> >
> > - __access_remote_vm() was already using vma_lookup() when the original
> >   lookup failed so by doing the lookup directly this also de-duplicates the
> >   code.
> >
> > We are able to perform these VMA operations as we already hold the
> > mmap_lock in order to be able to call get_user_pages_remote().
> >
> > As part of this work we add get_user_page_vma_remote() which abstracts the
> > VMA lookup, error handling and decrementing the page reference count should
> > the VMA lookup fail.
> >
> > This forms part of a broader set of patches intended to eliminate the vmas
> > parameter altogether.
> >
> > Reviewed-by: Catalin Marinas <catalin.marinas@arm.com> (for arm64)
> > Acked-by: David Hildenbrand <david@redhat.com>
> > Reviewed-by: Janosch Frank <frankja@linux.ibm.com> (for s390)
> > Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
> > ---
> >  arch/arm64/kernel/mte.c   | 17 +++++++++--------
> >  arch/s390/kvm/interrupt.c |  2 +-
> >  fs/exec.c                 |  2 +-
> >  include/linux/mm.h        | 34 +++++++++++++++++++++++++++++++---
> >  kernel/events/uprobes.c   | 13 +++++--------
> >  mm/gup.c                  | 12 ++++--------
> >  mm/memory.c               | 14 +++++++-------
> >  mm/rmap.c                 |  2 +-
> >  security/tomoyo/domain.c  |  2 +-
> >  virt/kvm/async_pf.c       |  3 +--
> >  10 files changed, 61 insertions(+), 40 deletions(-)
> >
>
> [...]
>
> > diff --git a/mm/memory.c b/mm/memory.c
> > index 146bb94764f8..63632a5eafc1 100644
> > --- a/mm/memory.c
> > +++ b/mm/memory.c
> > @@ -5590,7 +5590,6 @@ EXPORT_SYMBOL_GPL(generic_access_phys);
> >  int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> >  		       int len, unsigned int gup_flags)
> >  {
> > -	struct vm_area_struct *vma;
> >  	void *old_buf = buf;
> >  	int write = gup_flags & FOLL_WRITE;
> >
> > @@ -5599,13 +5598,15 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> >
> >  	/* ignore errors, just check how much was successfully transferred */
> >  	while (len) {
> > -		int bytes, ret, offset;
> > +		int bytes, offset;
> >  		void *maddr;
> > -		struct page *page = NULL;
> > +		struct vm_area_struct *vma;
> > +		struct page *page = get_user_page_vma_remote(mm, addr,
> > +							     gup_flags, &vma);
> > +
> > +		if (IS_ERR_OR_NULL(page)) {
> > +			int ret = 0;
>
> I see the warning below when building without CONFIG_HAVE_IOREMAP_PROT set.
>
> make --silent --keep-going --jobs=32 \
> O=/home/anders/.cache/tuxmake/builds/1244/build ARCH=arm \
> CROSS_COMPILE=arm-linux-gnueabihf- /home/anders/src/kernel/next/mm/memory.c: In function '__access_remote_vm':
> /home/anders/src/kernel/next/mm/memory.c:5608:29: warning: unused variable 'ret' [-Wunused-variable]
>  5608 |                         int ret = 0;
>       |                             ^~~
>

Ah damn, nice spot thanks!

>
> >
> > -		ret = get_user_pages_remote(mm, addr, 1,
> > -				gup_flags, &page, &vma, NULL);
> > -		if (ret <= 0) {
> >  #ifndef CONFIG_HAVE_IOREMAP_PROT
> >  			break;
> >  #else
> > @@ -5613,7 +5614,6 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
> >  			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
> >  			 * we can access using slightly different code.
> >  			 */
> > -			vma = vma_lookup(mm, addr);
> >  			if (!vma)
> >  				break;
> >  			if (vma->vm_ops && vma->vm_ops->access)
>
> Cheers,
> Anders

I enclose a -fix patch for this below:-

----8<----
From 6a4bb033a1ec60920e4945e7e063443f91489d06 Mon Sep 17 00:00:00 2001
From: Lorenzo Stoakes <lstoakes@gmail.com>
Date: Tue, 16 May 2023 19:16:22 +0100
Subject: [PATCH] mm/gup: remove vmas parameter from get_user_pages_remote()

Fix unused variable warning as reported by Anders Roxell.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>

---
 mm/memory.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 63632a5eafc1..b1b25e61294a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5605,11 +5605,11 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 							     gup_flags, &vma);

 		if (IS_ERR_OR_NULL(page)) {
-			int ret = 0;
-
 #ifndef CONFIG_HAVE_IOREMAP_PROT
 			break;
 #else
+			int ret = 0;
+
 			/*
 			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
 			 * we can access using slightly different code.
--
2.40.1

Re: [PATCH v5 3/6] mm/gup: remove vmas parameter from get_user_pages_remote()

[Andrew Morton]

On Tue, 16 May 2023 11:49:19 +0200 Anders Roxell <anders.roxell@linaro.org> wrote:

> On 2023-05-14 22:26, Lorenzo Stoakes wrote:
> > The only instances of get_user_pages_remote() invocations which used the
> > vmas parameter were for a single page which can instead simply look up the
> > VMA directly. In particular:-
> > 
> > - __update_ref_ctr() looked up the VMA but did nothing with it so we simply
> >   remove it.
> > 
> > - __access_remote_vm() was already using vma_lookup() when the original
> >   lookup failed so by doing the lookup directly this also de-duplicates the
> >   code.
> > 
> > We are able to perform these VMA operations as we already hold the
> > mmap_lock in order to be able to call get_user_pages_remote().
> > 
> > As part of this work we add get_user_page_vma_remote() which abstracts the
> > VMA lookup, error handling and decrementing the page reference count should
> > the VMA lookup fail.
> > 
> > This forms part of a broader set of patches intended to eliminate the vmas
> > parameter altogether.
> > 
> > -		int bytes, ret, offset;
> > +		int bytes, offset;
> >  		void *maddr;
> > -		struct page *page = NULL;
> > +		struct vm_area_struct *vma;
> > +		struct page *page = get_user_page_vma_remote(mm, addr,
> > +							     gup_flags, &vma);
> > +
> > +		if (IS_ERR_OR_NULL(page)) {
> > +			int ret = 0;
> 
> I see the warning below when building without CONFIG_HAVE_IOREMAP_PROT set.
> 
> make --silent --keep-going --jobs=32 \
> O=/home/anders/.cache/tuxmake/builds/1244/build ARCH=arm \
> CROSS_COMPILE=arm-linux-gnueabihf- /home/anders/src/kernel/next/mm/memory.c: In function '__access_remote_vm':
> /home/anders/src/kernel/next/mm/memory.c:5608:29: warning: unused variable 'ret' [-Wunused-variable]
>  5608 |                         int ret = 0;
>       |                             ^~~

Thanks, I did the obvious.

Also s/ret/res/, as `ret' is kinda reserved for "this is what this
function will return".

--- a/mm/memory.c~mm-gup-remove-vmas-parameter-from-get_user_pages_remote-fix
+++ a/mm/memory.c
@@ -5605,11 +5605,11 @@ int __access_remote_vm(struct mm_struct
 							     gup_flags, &vma);
 
 		if (IS_ERR_OR_NULL(page)) {
-			int ret = 0;
-
 #ifndef CONFIG_HAVE_IOREMAP_PROT
 			break;
 #else
+			int res = 0;
+
 			/*
 			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
 			 * we can access using slightly different code.
@@ -5617,11 +5617,11 @@ int __access_remote_vm(struct mm_struct
 			if (!vma)
 				break;
 			if (vma->vm_ops && vma->vm_ops->access)
-				ret = vma->vm_ops->access(vma, addr, buf,
+				res = vma->vm_ops->access(vma, addr, buf,
 							  len, write);
-			if (ret <= 0)
+			if (res <= 0)
 				break;
-			bytes = ret;
+			bytes = res;
 #endif
 		} else {
 			bytes = len;
_