From e7ff4ebffe3bedf55560ef861d80f6500ff0d76f Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 2 Aug 2024 08:46:18 -0700 Subject: [PATCH] x86/tsc: Check for sockets instead of CPUs to make code match comment The unsynchronized_tsc() eventually checks num_possible_cpus(), and if the system is non-Intel and the number of possible CPUs is greater than one, assumes that TSCs are unsynchronized. This despite the comment saying "assume multi socket systems are not synchronized", that is, socket rather than CPU. This behavior was preserved by commit 8fbbc4b45ce3 ("x86: merge tsc_init and clocksource code") and by the previous relevant commit 7e69f2b1ead2 ("clocksource: Remove the update callback"). The clocksource drivers were added by commit 5d0cf410e94b ("Time: i386 Clocksource Drivers") back in 2006, and the comment still said "socket" rather than "CPU". Therefore, bravely (and perhaps foolishly) make the code match the comment. Note that it is possible to bypass both code and comment by booting with tsc=reliable, but this also disables the clocksource watchdog, which is undesirable when trust in the TSC is strictly limited. Reported-by: Zhengxu Chen Reported-by: Danielle Costantino Signed-off-by: Paul E. McKenney Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/all/20240802154618.4149953-5-paulmck@kernel.org --- arch/x86/kernel/tsc.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 0ced1870ed40..dfe6847fd99e 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -1288,7 +1288,7 @@ int unsynchronized_tsc(void) */ if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL) { /* assume multi socket systems are not synchronized: */ - if (num_possible_cpus() > 1) + if (topology_max_packages() > 1) return 1; }