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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Thu, 17 Sep 2020 18:53:41 -0700
Message-ID: <CAPcyv4gFz6vBVVp_aiX4i2rL+8fps3gTQGj5cYw8QESCf7=DfQ@mail.gmail.com>
Subject: Re: [PATCH] pmem: fix __copy_user_flushcache
To:     Mikulas Patocka <mpatocka@redhat.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Andrew Morton <akpm@linux-foundation.org>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Eric Sandeen <esandeen@redhat.com>,
        Dave Chinner <dchinner@redhat.com>,
        "Kani, Toshi" <toshi.kani@hpe.com>,
        "Norton, Scott J" <scott.norton@hpe.com>,
        "Tadakamadla, Rajesh (DCIG/CDI/HPS Perf)" 
        <rajesh.tadakamadla@hpe.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-nvdimm <linux-nvdimm@lists.01.org>
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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>