On Fri, Jun 21, 2019 at 10:48:25AM -0700, Andi Kleen wrote:
> On Fri, Jun 14, 2019 at 01:28:53PM +0200, 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)
> >
> > We could also check if LBR tracing is enabled and make
> > appropriate checks, but this change is simpler ;-)
> >
> > ideas? thanks,
> > jirka
>
> Sorry for the late comment. I see this patch has been merged now.
>
> Unfortunately I don't think it's a good idea. The problem
> is that the hypervisor flags are only set for a few hypervisors
> that Linux knows about. But in practice there are many more
> Hypervisors around that will not cause these flags to be set.
> But these are still likely to miss MSRs.
>
> The other hypervisors are relatively obscure, but eventually
> someone will hit problems.
any idea if there's any other flag/way we could use to detect those?
adding few virtualization folks to the loop
and attaching the original patch
thanks,
jirka
---
Tom Vaden reported false failure of check_msr function, because
some servers can do POST tracing and enable LBR tracing during
the boot.
Kan confirmed that check_msr patch was to fix a bug report in
guest, so it's ok to disable it for real HW.
Cc: Kan Liang <kan.li...@intel.com>
Reported-by: Tom Vaden <tom.va...@hpe.com>
Signed-off-by: Jiri Olsa <jo...@kernel.org>
---
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
--
2.21.0
