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charset="utf-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 19AB7C0013 X-Stat-Signature: r6zszyqy8odxnpaoc1ki7kxpko6q8346 X-Rspam-User: X-HE-Tag: 1749161531-803609 X-HE-Meta: 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 LyOpSwT8 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jun 05, 2025, James Houghton wrote: > On Thu, Jun 5, 2025 at 8:38=E2=80=AFAM Fuad Tabba wrot= e: > > @@ -34,12 +36,83 @@ static void test_file_read_write(int fd) > > "pwrite on a guest_mem fd should fail"); > > } > > > > -static void test_mmap(int fd, size_t page_size) > > +static void test_mmap_supported(int fd, size_t page_size, size_t total= _size) > > +{ > > + const char val =3D 0xaa; > > + char *mem; >=20 > This must be `volatile char *` to ensure that the compiler doesn't > elide the accesses you have written. >=20 > > + size_t i; > > + int ret; > > + > > + mem =3D mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_PRIV= ATE, fd, 0); > > + TEST_ASSERT(mem =3D=3D MAP_FAILED, "Copy-on-write not allowed b= y guest_memfd."); > > + > > + mem =3D mmap(NULL, total_size, PROT_READ | PROT_WRITE, MAP_SHAR= ED, fd, 0); > > + TEST_ASSERT(mem !=3D MAP_FAILED, "mmap() for shared guest memor= y should succeed."); > > + > > + memset(mem, val, total_size); >=20 > Now unfortunately, `memset` and `munmap` will complain about the > volatile qualification. So... >=20 > memset((char *)mem, val, total_size); >=20 > Eh... wish they just wouldn't complain, but this is a small price to > pay for correctness. :) >=20 > > + for (i =3D 0; i < total_size; i++) > > + TEST_ASSERT_EQ(mem[i], val); >=20 > The compiler is allowed to[1] elide the read of `mem[i]` and just > assume that it is `val`. I don't think "volatile" is needed. Won't READ_ONCE(mem[i]) do the trick? = That in turn will force the compiler to emit the stores as well. > [1]: https://godbolt.org/z/Wora54bP6 >=20 > Feel free to add `volatile` to that snippet to see how the code changes.