On Sun, Jul 10, 2022 at 12:01:36PM +0200, Fabio M. De Francesco wrote: > The use of kmap_atomic() is being deprecated in favor of kmap_local_page(). > > With kmap_local_page(), the mappings are per thread, CPU local, not > globally visible and can take page faults. Furthermore, the mappings can be > acquired from any context (including interrupts). > > Therefore, use kmap_local_page() in copy_string_kernel() instead of > kmap_atomic(). > > Tested with xfstests on a QEMU + KVM 32-bits VM booting a kernel with > HIGHMEM64GB enabled. > > Suggested-by: Ira Weiny <ira.weiny@xxxxxxxxx> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@xxxxxxxxx> > --- > > I sent a first patch to fs/exec.c for converting kmap() and kmap_atomic() > to kmap_local_page(): > https://lore.kernel.org/lkml/20220630163527.9776-1-fmdefrancesco@xxxxxxxxx/ > > Some days ago, Ira Weiny, while he was reviewing that patch, made me notice > that I had overlooked a second kmap_atomic() in the same file (thanks): > https://lore.kernel.org/lkml/YsiQptk19txHrG4c@iweiny-desk3/ > > I've been asked to send this as an additional change. This is why there will > not be any second version of that previous patch. > > fs/exec.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/exec.c b/fs/exec.c > index 4a2129c0d422..5fa652ca5823 100644 > --- a/fs/exec.c > +++ b/fs/exec.c > @@ -639,11 +639,11 @@ int copy_string_kernel(const char *arg, struct linux_binprm *bprm) > page = get_arg_page(bprm, pos, 1); > if (!page) > return -E2BIG; > - kaddr = kmap_atomic(page); > + kaddr = kmap_local_page(page); > flush_arg_page(bprm, pos & PAGE_MASK, page); I really question why we can't use memcpy_to_page() here and move the flush_arg_page() prior to the mapping? flush_arg_page() only calls flush_cache_page() which does not need the mapping to work correctly AFAICT. Ira > memcpy(kaddr + offset_in_page(pos), arg, bytes_to_copy); > flush_dcache_page(page); > - kunmap_atomic(kaddr); > + kunmap_local(kaddr); > put_arg_page(page); > } > > -- > 2.36.1 >
