linux-kernel - [PATCH v13 09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering TSC frequency

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Message-ID: <20241021055156.2342564-10-nikunj@amd.com>
Date: Mon, 21 Oct 2024 11:21:52 +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 v13 09/13] tsc: Use the GUEST_TSC_FREQ MSR for discovering TSC frequency

Calibrating the TSC frequency using the kvmclock is not correct for
SecureTSC enabled guests. Use the platform provided TSC frequency via the
GUEST_TSC_FREQ MSR (C001_0134h).

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/coco/sev/core.c   | 16 ++++++++++++++++
 arch/x86/kernel/tsc.c      |  5 +++++
 3 files changed, 23 insertions(+)

diff --git a/arch/x86/include/asm/sev.h b/arch/x86/include/asm/sev.h
index 9169b18eeb78..34f7b9fc363b 100644
--- a/arch/x86/include/asm/sev.h
+++ b/arch/x86/include/asm/sev.h
@@ -536,6 +536,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
 }
 
 void __init snp_secure_tsc_prepare(void);
+void __init securetsc_init(void);
 
 #else	/* !CONFIG_AMD_MEM_ENCRYPT */
 
@@ -584,6 +585,7 @@ static inline int handle_guest_request(struct snp_msg_desc *mdesc, u64 exit_code
 				       u32 resp_sz) { return -ENODEV; }
 
 static inline void __init snp_secure_tsc_prepare(void) { }
+static inline void __init securetsc_init(void) { }
 
 #endif	/* CONFIG_AMD_MEM_ENCRYPT */
 
diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 4e9b1cc1f26b..154d568c59cf 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -3065,3 +3065,19 @@ void __init snp_secure_tsc_prepare(void)
 
 	pr_debug("SecureTSC enabled");
 }
+
+static unsigned long securetsc_get_tsc_khz(void)
+{
+	unsigned long long tsc_freq_mhz;
+
+	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
+	rdmsrl(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz);
+
+	return (unsigned long)(tsc_freq_mhz * 1000);
+}
+
+void __init securetsc_init(void)
+{
+	x86_platform.calibrate_cpu = securetsc_get_tsc_khz;
+	x86_platform.calibrate_tsc = securetsc_get_tsc_khz;
+}
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index dfe6847fd99e..c83f1091bb4f 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -30,6 +30,7 @@
 #include <asm/i8259.h>
 #include <asm/topology.h>
 #include <asm/uv/uv.h>
+#include <asm/sev.h>
 
 unsigned int __read_mostly cpu_khz;	/* TSC clocks / usec, not used here */
 EXPORT_SYMBOL(cpu_khz);
@@ -1514,6 +1515,10 @@ void __init tsc_early_init(void)
 	/* Don't change UV TSC multi-chassis synchronization */
 	if (is_early_uv_system())
 		return;
+
+	if (cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
+		securetsc_init();
+
 	if (!determine_cpu_tsc_frequencies(true))
 		return;
 	tsc_enable_sched_clock();
-- 
2.34.1