linux-kernel - Re: [PATCH v2 2/3] selftests/memfd

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Date: Tue, 26 Mar 2024 16:36:16 +0100
From: David Hildenbrand <david@...hat.com>
To: Miklos Szeredi <mszeredi@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Andrew Morton <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>,
 Lorenzo Stoakes <lstoakes@...il.com>, xingwei lee <xrivendell7@...il.com>,
 yue sun <samsun1006219@...il.com>
Subject: Re: [PATCH v2 2/3] selftests/memfd_secret: add vmsplice() test

>> +static void test_vmsplice(int fd, const char *desc)
>> +{
>> +       ssize_t transferred;
>> +       struct iovec iov;
>> +       int pipefd[2];
>> +       char *mem;
>> +
>> +       if (pipe(pipefd)) {
>> +               fail("pipe failed: %s\n", strerror(errno));
>> +               return;
>> +       }
>> +
>> +       mem = mmap(NULL, page_size, prot, mode, fd, 0);
>> +       if (mem == MAP_FAILED) {
>> +               fail("Unable to mmap secret memory\n");
>> +               goto close_pipe;
>> +       }
>> +
>> +       /*
>> +        * vmsplice() may use GUP-fast, which must also fail. Prefault the
>> +        * page table, so GUP-fast could find it.
>> +        */
>> +       memset(mem, PATTERN, page_size);
> 
> Shouldn't the non-prefault case be tested as well?

That's the "easy" case where GUP-fast is never involved, and it should 
mostly be covered by the ptrace/process_vm_read() tests already.

-- 
Cheers,

David / dhildenb