linux-kernel - Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <cd6c18f3-538a-494e-9e60-2caedb1f53c2@amd.com>
Date: Wed, 8 Jan 2025 15:50:08 +0530
From: "Nikunj A. Dadhania" <nikunj@....com>
To: Borislav Petkov <bp@...en8.de>
Cc: linux-kernel@...r.kernel.org, thomas.lendacky@....com, x86@...nel.org,
 kvm@...r.kernel.org, mingo@...hat.com, tglx@...utronix.de,
 dave.hansen@...ux.intel.com, pgonda@...gle.com, seanjc@...gle.com,
 pbonzini@...hat.com, francescolavra.fl@...il.com,
 Alexey Makhalov <alexey.makhalov@...adcom.com>,
 Juergen Gross <jgross@...e.com>, Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH v16 12/13] x86/tsc: Switch to native sched clock

On 1/8/2025 2:04 PM, Nikunj A. Dadhania wrote:
> 
>> If you want to take care only of STSC now, I'd take a patch which is known
>> good and tested properly. And that should happen very soon because the merge
>> window is closing in. 
> 
> In that case, let me limit this only to STSC for now, i will send updated patch.

From: Nikunj A Dadhania <nikunj@....com>
Date: Wed, 8 Jan 2025 14:18:04 +0530
Subject: [PATCH] x86/kvmclock: Prefer TSC as the scheduler clock for Secure
 TSC guests

Although the kernel switches over to a stable TSC clocksource instead of
kvmclock, the scheduler still keeps on using kvmclock as the sched clock.
This is due to kvm_sched_clock_init() updating the pv_sched_clock()
unconditionally. Do not override the PV sched clock when Secure TSC is
enabled.

Signed-off-by: Nikunj A Dadhania <nikunj@....com>
---
 arch/x86/kernel/kvmclock.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index d8fef3a65a35..82c4743a5e7a 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -324,8 +324,10 @@ void __init kvmclock_init(void)
 	if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
 		pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);

-	flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
-	kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
+	if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC)) {
+		flags = pvclock_read_flags(&hv_clock_boot[0].pvti);
+		kvm_sched_clock_init(flags & PVCLOCK_TSC_STABLE_BIT);
+	}

 	x86_platform.calibrate_tsc = kvm_get_tsc_khz;
 	x86_platform.calibrate_cpu = kvm_get_tsc_khz;
-- 
2.34.1