Re: [RFC] perf/x86/intel: Disable check_msr for real hw

[Liang, Kan]

On 6/14/2019 7:28 AM, Jiri Olsa wrote:
> hi,
> the HPE server can do POST tracing and have enabled LBR
> tracing during the boot, which makes check_msr fail falsly.
>
> It looks like check_msr code was added only to check on guests
> MSR access, would it be then ok to disable check_msr for real
> hardware? (as in patch below)

Yes, the check_msr patch was to fix a bug report in guest.
I didn't get similar bug report for real hardware.
I think it should be OK to disable it for real hardware.

Thanks,
Kan

> We could also check if LBR tracing is enabled and make
> appropriate checks, but this change is simpler ;-)
>
> ideas? thanks,
> jirka
>
>
> ---
>   arch/x86/events/intel/core.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/events/intel/core.c b/arch/x86/events/intel/core.c
> index 71001f005bfe..1194ae7e1992 100644
> --- a/arch/x86/events/intel/core.c
> +++ b/arch/x86/events/intel/core.c
> @@ -20,6 +20,7 @@
>   #include <asm/intel-family.h>
>   #include <asm/apic.h>
>   #include <asm/cpu_device_id.h>
> +#include <asm/hypervisor.h>
>   
>   #include "../perf_event.h"
>   
> @@ -4050,6 +4051,13 @@ static bool check_msr(unsigned long msr, u64 mask)
>   {
>   	u64 val_old, val_new, val_tmp;
>   
> +	/*
> +	 * Disable the check for real HW, so we don't
> +	 * mess up with potentionaly enabled regs.
> +	 */
> +	if (hypervisor_is_type(X86_HYPER_NATIVE))
> +		return true;
> +
>   	/*
>   	 * Read the current value, change it and read it back to see if it
>   	 * matches, this is needed to detect certain hardware emulators