Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
clocksource: hyper-v: Skip unnecessary checks for the root partition
The HV_ACCESS_TSC_INVARIANT bit is always zero when Linux runs as the
root partition. The root partition will see directly what the hardware
provides.
The old logic in ms_hyperv_init_platform caused the native TSC clock
source to be incorrectly marked as unstable on x86. Fix it.
Skip the unnecessary checks in code for the root partition. Add one
extra comment in code to clarify the behavior.
Reviewed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
+19
-2
+10
-1
arch/x86/kernel/cpu/mshyperv.c
+10
-1
arch/x86/kernel/cpu/mshyperv.c
···
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565
machine_ops.crash_shutdown = hv_machine_crash_shutdown;
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#endif
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#endif
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+
/*
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+
* HV_ACCESS_TSC_INVARIANT is always zero for the root partition. Root
570
+
* partition doesn't need to write to synthetic MSR to enable invariant
571
+
* TSC feature. It sees what the hardware provides.
572
+
*/
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if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
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/*
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* Writing to synthetic MSR 0x40000118 updates/changes the
···
641
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* TSC should be marked as unstable only after Hyper-V
642
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* clocksource has been initialized. This ensures that the
643
638
* stability of the sched_clock is not altered.
639
+
*
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* HV_ACCESS_TSC_INVARIANT is always zero for the root partition. No
641
+
* need to check for it.
644
642
*/
645
-
if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
643
+
if (!hv_root_partition() &&
644
+
!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
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mark_tsc_unstable("running on Hyper-V");
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hardlockup_detector_disable();
+9
-1
drivers/clocksource/hyperv_timer.c
+9
-1
drivers/clocksource/hyperv_timer.c
···
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union hv_reference_tsc_msr tsc_msr;
550
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/*
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+
* When running as a guest partition:
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+
*
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* If Hyper-V offers TSC_INVARIANT, then the virtualized TSC correctly
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* handles frequency and offset changes due to live migration,
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* pause/resume, and other VM management operations. So lower the
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* Hyper-V Reference TSC rating, causing the generic TSC to be used.
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* TSC_INVARIANT is not offered on ARM64, so the Hyper-V Reference
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* TSC will be preferred over the virtualized ARM64 arch counter.
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+
*
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* When running as the root partition:
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+
*
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+
* There is no HV_ACCESS_TSC_INVARIANT feature. Always lower the rating
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+
* of the Hyper-V Reference TSC.
558
565
*/
559
-
if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
566
+
if ((ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) ||
567
+
hv_root_partition()) {
560
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hyperv_cs_tsc.rating = 250;
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569
hyperv_cs_msr.rating = 245;
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}