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SubjectRe: [PATCH] pmem: fix __copy_user_flushcache
On Wed, Sep 16, 2020 at 11:57 AM Mikulas Patocka <mpatocka@redhat.com> wrote:
>
>
>
> On Wed, 16 Sep 2020, Dan Williams wrote:
>
> > On Wed, Sep 16, 2020 at 10:24 AM Mikulas Patocka <mpatocka@redhat.com> wrote:
> > >
> > >
> > >
> > > On Wed, 16 Sep 2020, Dan Williams wrote:
> > >
> > > > On Wed, Sep 16, 2020 at 3:57 AM Mikulas Patocka <mpatocka@redhat.com> wrote:
> > > > >
> > > > >
> > > > >
> > > > > I'm submitting this patch that adds the required exports (so that we could
> > > > > use __copy_from_user_flushcache on x86, arm64 and powerpc). Please, queue
> > > > > it for the next merge window.
> > > >
> > > > Why? This should go with the first user, and it's not clear that it
> > > > needs to be relative to the current dax_operations export scheme.
> > >
> > > Before nvfs gets included in the kernel, I need to distribute it as a
> > > module. So, it would make my maintenance easier. But if you don't want to
> > > export it now, no problem, I can just copy __copy_user_flushcache from the
> > > kernel to the module.
> >
> > That sounds a better plan than exporting symbols with no in-kernel consumer.
>
> BTW, this function is buggy. Here I'm submitting the patch.
>
>
>
> From: Mikulas Patocka <mpatocka@redhat.com>
>
> If we copy less than 8 bytes and if the destination crosses a cache line,
> __copy_user_flushcache would invalidate only the first cache line. This
> patch makes it invalidate the second cache line as well.

Good catch.

> Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> Cc: stable@vger.kernel.org
>
> ---
> arch/x86/lib/usercopy_64.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> Index: linux-2.6/arch/x86/lib/usercopy_64.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/lib/usercopy_64.c 2020-09-05 10:01:27.000000000 +0200
> +++ linux-2.6/arch/x86/lib/usercopy_64.c 2020-09-16 20:48:31.000000000 +0200
> @@ -120,7 +120,7 @@ long __copy_user_flushcache(void *dst, c
> */
> if (size < 8) {
> if (!IS_ALIGNED(dest, 4) || size != 4)
> - clean_cache_range(dst, 1);
> + clean_cache_range(dst, size);
> } else {
> if (!IS_ALIGNED(dest, 8)) {
> dest = ALIGN(dest, boot_cpu_data.x86_clflush_size);
>

You can add:

Fixes: 0aed55af8834 ("x86, uaccess: introduce
copy_from_iter_flushcache for pmem / cache-bypass operations")
Reviewed-by: Dan Williams <dan.j.wiilliams@intel.com>

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