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Re: [Xen-devel] [PATCH 1/2] x86/VPMU: Support only versions 2 and 3 of architectural performance monitoring



On 12/01/2015 04:01 AM, Dietmar Hahn wrote:
Am Montag 30 November 2015, 13:38:40 schrieb Boris Ostrovsky:
We need to have at least version 2 since it's the first version to
support various control and status registers (such as
MSR_CORE_PERF_GLOBAL_CTRL) that VPMU relies on always having.

With explicit testing for PMU version we can now remove CPUID model
check.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
  xen/arch/x86/cpu/vpmu_intel.c | 55 +++++++------------------------------------
  1 file changed, 8 insertions(+), 47 deletions(-)

diff --git a/xen/arch/x86/cpu/vpmu_intel.c b/xen/arch/x86/cpu/vpmu_intel.c
index d5ea7fe..bb4ddcc 100644
--- a/xen/arch/x86/cpu/vpmu_intel.c
+++ b/xen/arch/x86/cpu/vpmu_intel.c
@@ -955,59 +955,20 @@ int vmx_vpmu_initialise(struct vcpu *v)
  int __init core2_vpmu_init(void)
  {
      u64 caps;
+    unsigned int version = 0;
- if ( current_cpu_data.x86 != 6 )
+    if ( current_cpu_data.cpuid_level >= 0xa )
+        version = cpuid_eax(0xa) & 0xff;
+    if ( (version != 2) && (version != 3) )
      {
-        printk(XENLOG_WARNING "VPMU: only family 6 is supported\n");
+        printk(XENLOG_WARNING "VPMU: version %d is not supported\n", version);
          return -EINVAL;
But this means that all (newer?) processors with version=4 are not supported
even though the SDM 3B tells:
"Processors supporting architectural performance monitoring version 4 also
  supports version 1, 2, and 3, ..."

Shold we not only write a hint that version 4 capabilities are not supported
and fake this cpuid-flag for the guests to the version 3?

I in fact didn't know there was version 4 since I've always been looking at (apparently) old version of the SDM (Jan 2013).

We should indeed then downgrade version 4 to 3 as reported by .do_cpud() op.

-boris


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