linux-kernel - Re: [PATCH 3/4] mm: remove compat_sys_move

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Date:   Sat, 26 Sep 2020 17:21:29 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Eric Biederman <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>, kexec@...ts.infradead.org
Subject: Re: [PATCH 3/4] mm: remove compat_sys_move_pages

On Sat, Sep 19, 2020 at 7:38 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> I'd just keep the native version inline and have the compat one in
> a helper, but that is just a minor detail.

Folded in this change:

diff --git a/mm/migrate.c b/mm/migrate.c
index e9dfbde5f12c..d3fa3f4bf653 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1835,18 +1835,14 @@ static void do_pages_stat_array(struct
mm_struct *mm, unsigned long nr_pages,
        mmap_read_unlock(mm);
 }

-static int put_pages_array(const void __user *chunk_pages[],
-                          const void __user * __user *pages,
-                          unsigned long chunk_nr)
+static int put_compat_pages_array(const void __user *chunk_pages[],
+                                 const void __user * __user *pages,
+                                 unsigned long chunk_nr)
 {
        compat_uptr_t __user *pages32 = (compat_uptr_t __user *)pages;
        compat_uptr_t p;
        int i;

-       if (!in_compat_syscall())
-               return copy_from_user(chunk_pages, pages,
-                                     chunk_nr * sizeof(*chunk_pages));
-
        for (i = 0; i < chunk_nr; i++) {
                if (get_user(p, pages32 + i))
                        return -EFAULT;
@@ -1875,8 +1871,15 @@ static int do_pages_stat(struct mm_struct *mm,
unsigned long nr_pages,
                if (chunk_nr > DO_PAGES_STAT_CHUNK_NR)
                        chunk_nr = DO_PAGES_STAT_CHUNK_NR;

-               if (put_pages_array(chunk_pages, pages, chunk_nr))
-                       break;
+               if (in_compat_syscall()) {
+                       if (put_compat_pages_array(chunk_pages, pages,
+                                                  chunk_nr))
+                               break;
+               } else {
+                       if (copy_from_user(chunk_pages, pages,
+                                     chunk_nr * sizeof(*chunk_pages)))
+                               break;
+               }

                do_pages_stat_array(mm, chunk_nr, chunk_pages, chunk_status);

It does make the separation cleaner but it's also more code, which is
why I had it in the combined function before.

      Arnd