linux-kernel - [PATCH v11 19/20] x86/kvmclock: Skip kvmclock when Secure TSC is available

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Message-ID: <20240731150811.156771-20-nikunj@amd.com>
Date: Wed, 31 Jul 2024 20:38:10 +0530
From: Nikunj A Dadhania <nikunj@....com>
To: <linux-kernel@...r.kernel.org>, <thomas.lendacky@....com>, <bp@...en8.de>,
	<x86@...nel.org>, <kvm@...r.kernel.org>
CC: <mingo@...hat.com>, <tglx@...utronix.de>, <dave.hansen@...ux.intel.com>,
	<pgonda@...gle.com>, <seanjc@...gle.com>, <pbonzini@...hat.com>,
	<nikunj@....com>
Subject: [PATCH v11 19/20] x86/kvmclock: Skip kvmclock when Secure TSC is available

For AMD SNP guests with SecureTSC enabled, kvm-clock is being picked up
momentarily instead of selecting more stable TSC clocksource.

[    0.000000] kvm-clock: Using msrs 4b564d01 and 4b564d00
[    0.000001] kvm-clock: using sched offset of 1799357702246960 cycles
[    0.001493] clocksource: kvm-clock: mask: 0xffffffffffffffff max_cycles: 0x1cd42e4dffb, max_idle_ns: 881590591483 ns
[    0.006289] tsc: Detected 1996.249 MHz processor
[    0.305123] clocksource: tsc-early: mask: 0xffffffffffffffff max_cycles: 0x398cadd9d93, max_idle_ns: 881590552906 ns
[    1.045759] clocksource: Switched to clocksource kvm-clock
[    1.141326] clocksource: tsc: mask: 0xffffffffffffffff max_cycles: 0x398cadd9d93, max_idle_ns: 881590552906 ns
[    1.144634] clocksource: Switched to clocksource tsc

When Secure TSC is enabled, skip using the kvmclock. The guest kernel will
fallback and use Secure TSC based clocksource.

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
Tested-by: Peter Gonda <pgonda@...gle.com>
---
 arch/x86/kernel/kvmclock.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 5b2c15214a6b..3d03b4c937b9 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -289,7 +289,7 @@ void __init kvmclock_init(void)
 {
 	u8 flags;
 
-	if (!kvm_para_available() || !kvmclock)
+	if (!kvm_para_available() || !kvmclock || cc_platform_has(CC_ATTR_GUEST_SECURE_TSC))
 		return;
 
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE2)) {
-- 
2.34.1