On venerdì 22 luglio 2022 02:14:20 CEST Ira Weiny wrote: > 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.we...@intel.com> > > Signed-off-by: Fabio M. De Francesco <fmdefrance...@gmail.com> > > --- > > > > 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-fmdefrance...@gmail.com/ > > > > 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.
You're right here. I'm sorry for being so lazy and not checking that flush_arg_page() does not need to be called while the task holds the local mapping :-( In v2 I'll move flush_arg_page() one line above memcpy_to_page(). Thanks for your comment, Fabio > > 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 > > >
