linux-kernel - [PATCH] x86/tsc: Use rdtsc_ordered() when RDTSCP or LFENCE

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Message-ID: <20240823042508.1057791-3-superm1@kernel.org>
Date: Thu, 22 Aug 2024 23:25:04 -0500
From: Mario Limonciello <superm1@...nel.org>
To: Bjorn Helgaas <bhelgaas@...gle.com>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: "open list : PCI SUBSYSTEM" <linux-pci@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list : USB XHCI DRIVER" <linux-usb@...r.kernel.org>,
	Daniel Drake <drake@...lessos.org>,
	Gary Li <Gary.Li@....com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Mario Limonciello <mario.limonciello@....com>
Subject: [PATCH] x86/tsc: Use rdtsc_ordered() when RDTSCP or LFENCE_RDTSC are supported

From: Mario Limonciello <mario.limonciello@....com>

On AMD processors the TSC has been reported drifting on and off for
various platforms.  This has been root caused to becaused by out of order
TSC and HPET counter values.  When the SoC supports RDTSCP or LFENCE_RDTSC
use ordered tsc reads instead.

Signed-off-by: Mario Limonciello <mario.limonciello@....com>
---
 arch/x86/include/asm/tsc.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h
index 94408a784c8e7..1c0cda1702bec 100644
--- a/arch/x86/include/asm/tsc.h
+++ b/arch/x86/include/asm/tsc.h
@@ -24,6 +24,9 @@ static inline cycles_t get_cycles(void)
 	if (!IS_ENABLED(CONFIG_X86_TSC) &&
 	    !cpu_feature_enabled(X86_FEATURE_TSC))
 		return 0;
+	if (cpu_feature_enabled(X86_FEATURE_LFENCE_RDTSC) ||
+	    cpu_feature_enabled(X86_FEATURE_RDTSCP))
+		return rdtsc_ordered();
 	return rdtsc();
 }
 #define get_cycles get_cycles
-- 
2.43.0