[kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Maxim Levitsky]

While this is not likely, it is valid for the MSR_LBR_TOS
to contain 0 value, after a test which issues a series of branches, if the
number of branches recorded was divisible by the number of LBR msrs.

This unfortunately depends on the compiler, the number of LBR registers,
and it is not even deterministic between different runs of the test,
because interrupts, rescheduling, and various other events can affect total
number of branches done.

Therefore drop the check, instead of trying to fix it.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
 x86/pmu_lbr.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
index c6f010847..8ca8ed044 100644
--- a/x86/pmu_lbr.c
+++ b/x86/pmu_lbr.c
@@ -98,7 +98,6 @@ int main(int ac, char **av)
 	lbr_test();
 	wrmsr(MSR_IA32_DEBUGCTLMSR, 0);
 
-	report(rdmsr(MSR_LBR_TOS) != 0, "The guest LBR MSR_LBR_TOS value is good.");
 	for (i = 0; i < max; ++i) {
 		if (!rdmsr(lbr_to + i) || !rdmsr(lbr_from + i))
 			break;
-- 
2.26.3

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Maxim Levitsky]

On Wed, 2024-10-02 at 19:56 -0400, Maxim Levitsky wrote:
> While this is not likely, it is valid for the MSR_LBR_TOS
> to contain 0 value, after a test which issues a series of branches, if the
> number of branches recorded was divisible by the number of LBR msrs.
> 
> This unfortunately depends on the compiler, the number of LBR registers,
> and it is not even deterministic between different runs of the test,
> because interrupts, rescheduling, and various other events can affect total
> number of branches done.
> 
> Therefore drop the check, instead of trying to fix it.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  x86/pmu_lbr.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
> index c6f010847..8ca8ed044 100644
> --- a/x86/pmu_lbr.c
> +++ b/x86/pmu_lbr.c
> @@ -98,7 +98,6 @@ int main(int ac, char **av)
>  	lbr_test();
>  	wrmsr(MSR_IA32_DEBUGCTLMSR, 0);
>  
> -	report(rdmsr(MSR_LBR_TOS) != 0, "The guest LBR MSR_LBR_TOS value is good.");
>  	for (i = 0; i < max; ++i) {
>  		if (!rdmsr(lbr_to + i) || !rdmsr(lbr_from + i))
>  			break;

A very kind ping on this patch.

Best regards,
        Maxim Levitsky

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Maxim Levitsky]

On Sun, 2024-11-03 at 16:06 -0500, Maxim Levitsky wrote:
> A very kind ping on this patch.
> 
> 
> 
> Best regards,
> 
>         Maxim Levitsky

Another very kind ping on this patch.

Best regards,
        Maxim Levitsky

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Maxim Levitsky]

On Thu, 2024-11-21 at 20:33 -0500, Maxim Levitsky wrote:
> On Sun, 2024-11-03 at 16:06 -0500, Maxim Levitsky wrote:
> > A very kind ping on this patch.
> > 
> > 
> > 
> > Best regards,
> > 
> >         Maxim Levitsky
> 
> Another very kind ping on this patch.


Any update?

Best regards,
	Maxim Levitsky

> 
> Best regards,
>         Maxim Levitsky
> 

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Maxim Levitsky]

On Wed, 2024-10-02 at 19:56 -0400, Maxim Levitsky wrote:
> While this is not likely, it is valid for the MSR_LBR_TOS
> to contain 0 value, after a test which issues a series of branches, if the
> number of branches recorded was divisible by the number of LBR msrs.
> 
> This unfortunately depends on the compiler, the number of LBR registers,
> and it is not even deterministic between different runs of the test,
> because interrupts, rescheduling, and various other events can affect total
> number of branches done.
> 
> Therefore drop the check, instead of trying to fix it.
> 
> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> ---
>  x86/pmu_lbr.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
> index c6f010847..8ca8ed044 100644
> --- a/x86/pmu_lbr.c
> +++ b/x86/pmu_lbr.c
> @@ -98,7 +98,6 @@ int main(int ac, char **av)
>  	lbr_test();
>  	wrmsr(MSR_IA32_DEBUGCTLMSR, 0);
>  
> -	report(rdmsr(MSR_LBR_TOS) != 0, "The guest LBR MSR_LBR_TOS value is good.");
>  	for (i = 0; i < max; ++i) {
>  		if (!rdmsr(lbr_to + i) || !rdmsr(lbr_from + i))
>  			break;

Hi,

This is the other kvm-unit-tests patch that I have a ticket open for,
and I would like to get this merged and close the ticket.

Thanks,
Best regards,
	Maxim Levitsky

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Sean Christopherson]

On Tue, Feb 18, 2025, Maxim Levitsky wrote:
> On Wed, 2024-10-02 at 19:56 -0400, Maxim Levitsky wrote:
> > While this is not likely, it is valid for the MSR_LBR_TOS
> > to contain 0 value, after a test which issues a series of branches, if the
> > number of branches recorded was divisible by the number of LBR msrs.
> > 
> > This unfortunately depends on the compiler, the number of LBR registers,
> > and it is not even deterministic between different runs of the test,
> > because interrupts, rescheduling, and various other events can affect total
> > number of branches done.
> > 
> > Therefore drop the check, instead of trying to fix it.
> > 
> > Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
> > ---
> >  x86/pmu_lbr.c | 1 -
> >  1 file changed, 1 deletion(-)
> > 
> > diff --git a/x86/pmu_lbr.c b/x86/pmu_lbr.c
> > index c6f010847..8ca8ed044 100644
> > --- a/x86/pmu_lbr.c
> > +++ b/x86/pmu_lbr.c
> > @@ -98,7 +98,6 @@ int main(int ac, char **av)
> >  	lbr_test();
> >  	wrmsr(MSR_IA32_DEBUGCTLMSR, 0);
> >  
> > -	report(rdmsr(MSR_LBR_TOS) != 0, "The guest LBR MSR_LBR_TOS value is good.");
> >  	for (i = 0; i < max; ++i) {
> >  		if (!rdmsr(lbr_to + i) || !rdmsr(lbr_from + i))
> >  			break;
> 
> Hi,
> 
> This is the other kvm-unit-tests patch that I have a ticket open for,
> and I would like to get this merged and close the ticket.

I'll grab it.  I'm hoping to get the pull request put together tomorrow, but I
might not get to it until Thusrday.

Re: [kvm-unit-tests PATCH] pmu_lbr: drop check for MSR_LBR_TOS != 0

[Sean Christopherson]

On Wed, 02 Oct 2024 19:56:58 -0400, Maxim Levitsky wrote:
> While this is not likely, it is valid for the MSR_LBR_TOS
> to contain 0 value, after a test which issues a series of branches, if the
> number of branches recorded was divisible by the number of LBR msrs.
> 
> This unfortunately depends on the compiler, the number of LBR registers,
> and it is not even deterministic between different runs of the test,
> because interrupts, rescheduling, and various other events can affect total
> number of branches done.
> 
> [...]

Applied to kvm-x86 next (and now pulled by Paolo), thanks!

[1/1] pmu_lbr: drop check for MSR_LBR_TOS != 0
      https://github.com/kvm-x86/kvm-unit-tests/commit/584a927eaf58

--
https://github.com/kvm-x86/kvm-unit-tests/tree/next