On Tue, 16 May 2023 11:49:19 +0200 Anders Roxell <anders.roxell@xxxxxxxxxx> 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;
_
