[PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[Like Xu]

Some new Intel platforms (such as TGL) already have the
fourth fixed counter TOPDOWN.SLOTS, but it has not been
fully enabled on KVM and the host.

Therefore, we limit edx.split.num_counters_fixed to 3,
so that it does not break the kvm-unit-tests PMU test
case and bad-handled userspace.

Signed-off-by: Like Xu <like.xu@linux.intel.com>
---
 arch/x86/kvm/cpuid.c | 2 +-
 arch/x86/kvm/pmu.h   | 2 ++
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 8a294f9747aa..0a2c6d2b4650 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -604,7 +604,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
 		eax.split.bit_width = cap.bit_width_gp;
 		eax.split.mask_length = cap.events_mask_len;
 
-		edx.split.num_counters_fixed = cap.num_counters_fixed;
+		edx.split.num_counters_fixed = min(cap.num_counters_fixed, MAX_FIXED_COUNTERS);
 		edx.split.bit_width_fixed = cap.bit_width_fixed;
 		edx.split.reserved = 0;
 
diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
index ab85eed8a6cc..067fef51760c 100644
--- a/arch/x86/kvm/pmu.h
+++ b/arch/x86/kvm/pmu.h
@@ -15,6 +15,8 @@
 #define VMWARE_BACKDOOR_PMC_REAL_TIME		0x10001
 #define VMWARE_BACKDOOR_PMC_APPARENT_TIME	0x10002
 
+#define MAX_FIXED_COUNTERS	3
+
 struct kvm_event_hw_type_mapping {
 	u8 eventsel;
 	u8 unit_mask;
-- 
2.21.3

Re: [PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[Xu, Like]

Kindly ping.

I think we may need this patch, as we limit the maximum vPMU version to 2:
     eax.split.version_id = min(cap.version, 2);

Thanks,
Like Xu

On 2020/6/24 9:59, Like Xu wrote:
> Some new Intel platforms (such as TGL) already have the
> fourth fixed counter TOPDOWN.SLOTS, but it has not been
> fully enabled on KVM and the host.
>
> Therefore, we limit edx.split.num_counters_fixed to 3,
> so that it does not break the kvm-unit-tests PMU test
> case and bad-handled userspace.
>
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> ---
>   arch/x86/kvm/cpuid.c | 2 +-
>   arch/x86/kvm/pmu.h   | 2 ++
>   2 files changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8a294f9747aa..0a2c6d2b4650 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -604,7 +604,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>   		eax.split.bit_width = cap.bit_width_gp;
>   		eax.split.mask_length = cap.events_mask_len;
>   
> -		edx.split.num_counters_fixed = cap.num_counters_fixed;
> +		edx.split.num_counters_fixed = min(cap.num_counters_fixed, MAX_FIXED_COUNTERS);
>   		edx.split.bit_width_fixed = cap.bit_width_fixed;
>   		edx.split.reserved = 0;
>   
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index ab85eed8a6cc..067fef51760c 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -15,6 +15,8 @@
>   #define VMWARE_BACKDOOR_PMC_REAL_TIME		0x10001
>   #define VMWARE_BACKDOOR_PMC_APPARENT_TIME	0x10002
>   
> +#define MAX_FIXED_COUNTERS	3
> +
>   struct kvm_event_hw_type_mapping {
>   	u8 eventsel;
>   	u8 unit_mask;

Re: [PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[Paolo Bonzini]

On 24/06/20 03:59, Like Xu wrote:
> Some new Intel platforms (such as TGL) already have the
> fourth fixed counter TOPDOWN.SLOTS, but it has not been
> fully enabled on KVM and the host.
> 
> Therefore, we limit edx.split.num_counters_fixed to 3,
> so that it does not break the kvm-unit-tests PMU test
> case and bad-handled userspace.
> 
> Signed-off-by: Like Xu <like.xu@linux.intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 2 +-
>  arch/x86/kvm/pmu.h   | 2 ++
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 8a294f9747aa..0a2c6d2b4650 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -604,7 +604,7 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>  		eax.split.bit_width = cap.bit_width_gp;
>  		eax.split.mask_length = cap.events_mask_len;
>  
> -		edx.split.num_counters_fixed = cap.num_counters_fixed;
> +		edx.split.num_counters_fixed = min(cap.num_counters_fixed, MAX_FIXED_COUNTERS);
>  		edx.split.bit_width_fixed = cap.bit_width_fixed;
>  		edx.split.reserved = 0;
>  
> diff --git a/arch/x86/kvm/pmu.h b/arch/x86/kvm/pmu.h
> index ab85eed8a6cc..067fef51760c 100644
> --- a/arch/x86/kvm/pmu.h
> +++ b/arch/x86/kvm/pmu.h
> @@ -15,6 +15,8 @@
>  #define VMWARE_BACKDOOR_PMC_REAL_TIME		0x10001
>  #define VMWARE_BACKDOOR_PMC_APPARENT_TIME	0x10002
>  
> +#define MAX_FIXED_COUNTERS	3
> +
>  struct kvm_event_hw_type_mapping {
>  	u8 eventsel;
>  	u8 unit_mask;
> 

Queued, thanks.

Paolo

Re: [PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[Paolo Bonzini]

On 08/07/20 09:51, Xu, Like wrote:
> Kindly ping.
> 
> I think we may need this patch, as we limit the maximum vPMU version to 2:
>     eax.split.version_id = min(cap.version, 2);

I don't think this is a problem.  Are you planning to add support for
the fourth counter?

Paolo

Re: [PATCH] kvm: x86: limit the maximum number of vPMU fixed counters to 3

[Xu, Like]

On 2020/7/8 19:09, Paolo Bonzini wrote:
> On 08/07/20 09:51, Xu, Like wrote:
>> Kindly ping.
>>
>> I think we may need this patch, as we limit the maximum vPMU version to 2:
>>      eax.split.version_id = min(cap.version, 2);
> I don't think this is a problem.  Are you planning to add support for
> the fourth counter?
Yes, we plan to provide this support on the KVM after fully enabling the fourth
counter (and an accompanying special counter) on the host perf side.

This may require one or two kernel cycles, so I have to prevent it from
being exposed to non-linux guest with this fix. Thanks for your support.

Thanks,
Like Xu
>
> Paolo
>