Re: [PATCHv6 22/36] x86/vdso: Add offsets page in vvar

Hi Thomas,

On 8/15/19 8:21 PM, Thomas Gleixner wrote:

On Thu, 15 Aug 2019, Dmitry Safonov wrote:

quoted

---
 arch/Kconfig                          |  5 +++
 arch/x86/Kconfig                      |  1 +
 arch/x86/entry/vdso/vdso-layout.lds.S |  9 ++++-
 arch/x86/entry/vdso/vdso2c.c          |  3 ++
 arch/x86/entry/vdso/vma.c             | 12 +++++++
 arch/x86/include/asm/vdso.h           |  1 +
 init/Kconfig                          |  1 +
 lib/vdso/gettimeofday.c               | 47 +++++++++++++++++++++++++++

This needs to be split into the generic lib/vdso part and then x86 making
use of it.

Ok

quoted

+#ifdef CONFIG_TIME_NS

This should be COMPILE_WITH_TIME_NS and not CONFIG_TIME_NS

quoted

+extern u8 timens_page
+	__attribute__((visibility("hidden")));
+
+notrace static __always_inline void clk_to_ns(clockid_t clk, struct __kernel_timespec *ts)

This needs notrace because?

Heh, well it's alive from the time it was in arch/x86.
I believe, functions there had it since commit 23adec554a76 ("x86: add
notrace annotations to vsyscall"). Probably, lib/vdso is compiled
without mcount in the Makefile somewhere.
Will drop.

[..]

quoted

+	/*
+	 * The kernel allows to set a negative offset only if the current clock
+	 * value in a namespace is positive, so the result tv_sec can't be
+	 * negative here.
+	 */
+	ts->tv_nsec += offset64->tv_nsec;
+	ts->tv_sec += offset64->tv_sec;
+	if (ts->tv_nsec >= NSEC_PER_SEC) {
+		ts->tv_nsec -= NSEC_PER_SEC;
+		ts->tv_sec++;
+	}
+	if (ts->tv_nsec < 0) {
+		ts->tv_nsec += NSEC_PER_SEC;
+		ts->tv_sec--;
+	}

That's broken for 32bit user space on 64bit hosts. On LE due to
misalignment and on BE because 32bit will read always 0.

Ugh, will look into that.

Thanks,
          Dmitry