* [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0
@ 2021-07-16 13:32 Ani Sinha
2021-07-16 13:42 ` Vitaly Kuznetsov
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Ani Sinha @ 2021-07-16 13:32 UTC (permalink / raw)
To: linux-kernel
Cc: anirban.sinha, mikelley, Ani Sinha, K. Y. Srinivasan,
Haiyang Zhang, Stephen Hemminger, Wei Liu, Dexuan Cui,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H. Peter Anvin, linux-hyperv
Commit dce7cd62754b5 ("x86/hyperv: Allow guests to enable InvariantTSC")
added the support for HV_X64_MSR_TSC_INVARIANT_CONTROL. Setting bit 0
of this synthetic MSR will allow hyper-v guests to report invariant TSC
CPU feature through CPUID. This comment adds this explanation to the code
and mentions where the Intel's generic platform init code reads this
feature bit from CPUID. The comment will help developers understand how
the two parts of the initialization (hyperV specific and non-hyperV
specific generic hw init) are related.
Signed-off-by: Ani Sinha <ani@anisinha.ca>
---
arch/x86/kernel/cpu/mshyperv.c | 9 +++++++++
1 file changed, 9 insertions(+)
changelog:
v1: initial patch
v2: slight comment update based on received feedback.
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 715458b7729a..3b05dab3086e 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -368,6 +368,15 @@ static void __init ms_hyperv_init_platform(void)
machine_ops.crash_shutdown = hv_machine_crash_shutdown;
#endif
if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
+ /*
+ * Writing to synthetic MSR 0x40000118 updates/changes the
+ * guest visible CPUIDs. Setting bit 0 of this MSR enables
+ * guests to report invariant TSC feature through CPUID
+ * instruction, CPUID 0x800000007/EDX, bit 8. See code in
+ * early_init_intel() where this bit is examined. The
+ * setting of this MSR bit should happen before init_intel()
+ * is called.
+ */
wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1);
setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
}
--
2.25.1
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0
2021-07-16 13:32 [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0 Ani Sinha
@ 2021-07-16 13:42 ` Vitaly Kuznetsov
2021-07-16 13:59 ` Michael Kelley
2021-07-16 14:53 ` Wei Liu
2 siblings, 0 replies; 4+ messages in thread
From: Vitaly Kuznetsov @ 2021-07-16 13:42 UTC (permalink / raw)
To: Ani Sinha, linux-kernel
Cc: anirban.sinha, mikelley, Ani Sinha, K. Y. Srinivasan,
Haiyang Zhang, Stephen Hemminger, Wei Liu, Dexuan Cui,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H. Peter Anvin, linux-hyperv
Ani Sinha <ani@anisinha.ca> writes:
> Commit dce7cd62754b5 ("x86/hyperv: Allow guests to enable InvariantTSC")
> added the support for HV_X64_MSR_TSC_INVARIANT_CONTROL. Setting bit 0
> of this synthetic MSR will allow hyper-v guests to report invariant TSC
> CPU feature through CPUID. This comment adds this explanation to the code
> and mentions where the Intel's generic platform init code reads this
> feature bit from CPUID. The comment will help developers understand how
> the two parts of the initialization (hyperV specific and non-hyperV
> specific generic hw init) are related.
>
> Signed-off-by: Ani Sinha <ani@anisinha.ca>
> ---
> arch/x86/kernel/cpu/mshyperv.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> changelog:
> v1: initial patch
> v2: slight comment update based on received feedback.
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 715458b7729a..3b05dab3086e 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -368,6 +368,15 @@ static void __init ms_hyperv_init_platform(void)
> machine_ops.crash_shutdown = hv_machine_crash_shutdown;
> #endif
> if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
> + /*
> + * Writing to synthetic MSR 0x40000118 updates/changes the
> + * guest visible CPUIDs. Setting bit 0 of this MSR enables
> + * guests to report invariant TSC feature through CPUID
> + * instruction, CPUID 0x800000007/EDX, bit 8. See code in
> + * early_init_intel() where this bit is examined. The
> + * setting of this MSR bit should happen before init_intel()
> + * is called.
> + */
This should be very clear now, thanks!
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1);
> setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
> }
--
Vitaly
^ permalink raw reply [flat|nested] 4+ messages in thread
* RE: [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0
2021-07-16 13:32 [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0 Ani Sinha
2021-07-16 13:42 ` Vitaly Kuznetsov
@ 2021-07-16 13:59 ` Michael Kelley
2021-07-16 14:53 ` Wei Liu
2 siblings, 0 replies; 4+ messages in thread
From: Michael Kelley @ 2021-07-16 13:59 UTC (permalink / raw)
To: Ani Sinha, linux-kernel
Cc: anirban.sinha, KY Srinivasan, Haiyang Zhang, Stephen Hemminger,
Wei Liu, Dexuan Cui, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, x86, H. Peter Anvin, linux-hyperv
From: Ani Sinha <ani@anisinha.ca> Sent: Friday, July 16, 2021 6:33 AM
>
> Commit dce7cd62754b5 ("x86/hyperv: Allow guests to enable InvariantTSC")
> added the support for HV_X64_MSR_TSC_INVARIANT_CONTROL. Setting bit 0
> of this synthetic MSR will allow hyper-v guests to report invariant TSC
> CPU feature through CPUID. This comment adds this explanation to the code
> and mentions where the Intel's generic platform init code reads this
> feature bit from CPUID. The comment will help developers understand how
> the two parts of the initialization (hyperV specific and non-hyperV
> specific generic hw init) are related.
>
> Signed-off-by: Ani Sinha <ani@anisinha.ca>
> ---
> arch/x86/kernel/cpu/mshyperv.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> changelog:
> v1: initial patch
> v2: slight comment update based on received feedback.
>
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 715458b7729a..3b05dab3086e 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -368,6 +368,15 @@ static void __init ms_hyperv_init_platform(void)
> machine_ops.crash_shutdown = hv_machine_crash_shutdown;
> #endif
> if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) {
> + /*
> + * Writing to synthetic MSR 0x40000118 updates/changes the
> + * guest visible CPUIDs. Setting bit 0 of this MSR enables
> + * guests to report invariant TSC feature through CPUID
> + * instruction, CPUID 0x800000007/EDX, bit 8. See code in
> + * early_init_intel() where this bit is examined. The
> + * setting of this MSR bit should happen before init_intel()
> + * is called.
> + */
> wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1);
> setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE);
> }
> --
> 2.25.1
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0
2021-07-16 13:32 [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0 Ani Sinha
2021-07-16 13:42 ` Vitaly Kuznetsov
2021-07-16 13:59 ` Michael Kelley
@ 2021-07-16 14:53 ` Wei Liu
2 siblings, 0 replies; 4+ messages in thread
From: Wei Liu @ 2021-07-16 14:53 UTC (permalink / raw)
To: Ani Sinha
Cc: linux-kernel, anirban.sinha, mikelley, K. Y. Srinivasan,
Haiyang Zhang, Stephen Hemminger, Wei Liu, Dexuan Cui,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, x86,
H. Peter Anvin, linux-hyperv
On Fri, Jul 16, 2021 at 07:02:45PM +0530, Ani Sinha wrote:
> Commit dce7cd62754b5 ("x86/hyperv: Allow guests to enable InvariantTSC")
> added the support for HV_X64_MSR_TSC_INVARIANT_CONTROL. Setting bit 0
> of this synthetic MSR will allow hyper-v guests to report invariant TSC
> CPU feature through CPUID. This comment adds this explanation to the code
> and mentions where the Intel's generic platform init code reads this
> feature bit from CPUID. The comment will help developers understand how
> the two parts of the initialization (hyperV specific and non-hyperV
> specific generic hw init) are related.
>
> Signed-off-by: Ani Sinha <ani@anisinha.ca>
Applied to hyperv-next. Thanks.
^ permalink raw reply [flat|nested] 4+ messages in thread
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2021-07-16 13:32 [PATCH v2] x86/hyperv: add comment describing TSC_INVARIANT_CONTROL MSR setting bit 0 Ani Sinha
2021-07-16 13:42 ` Vitaly Kuznetsov
2021-07-16 13:59 ` Michael Kelley
2021-07-16 14:53 ` Wei Liu
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