linux-kernel - Re: [PATCH kvm-unit-tests] x86/pmu: Add Intel Guest Transactional (commited) cycles testcase

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Date:   Wed, 7 Dec 2022 23:51:18 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Like Xu <like.xu.linux@...il.com>
CC:     <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH kvm-unit-tests] x86/pmu: Add Intel Guest Transactional
 (commited) cycles testcase


On 12/7/2022 3:15 PM, Like Xu wrote:
> From: Like Xu <likexu@...cent.com>
>
> On Intel platforms with TSX feature, pmu users in guest can collect
> the commited or total transactional cycles for a tsx-enabled workload,
> adding new test cases to cover them, as they are not strictly the same
> as normal hardware events from the KVM implementation point of view.
>
> Signed-off-by: Like Xu <likexu@...cent.com>
> ---
>   x86/pmu.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 72 insertions(+), 1 deletion(-)
>
> diff --git a/x86/pmu.c b/x86/pmu.c
> index 72c2c9c..d4c6813 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -20,7 +20,7 @@
>   
>   typedef struct {
>   	uint32_t ctr;
> -	uint32_t config;
> +	uint64_t config;
>   	uint64_t count;
>   	int idx;
>   } pmu_counter_t;
> @@ -547,6 +547,76 @@ static void check_emulated_instr(void)
>   	report_prefix_pop();
>   }
>   
> +#define _XBEGIN_STARTED		(~0u)
> +
> +static inline int _xbegin(void)
> +{
> +	int ret = _XBEGIN_STARTED;
> +	asm volatile(".byte 0xc7,0xf8 ; .long 0" : "+a" (ret) :: "memory");
> +	return ret;
> +}
> +
> +static inline void _xend(void)
> +{
> +	asm volatile(".byte 0x0f,0x01,0xd5" ::: "memory");
> +}
> +
> +int *ptr;
> +
> +static void tsx_fault(void)
> +{
> +	int value = 0;
> +
> +	ptr = NULL;
> +	if(_xbegin() == _XBEGIN_STARTED) {
> +		value++;
> +		// causes abort
> +		*ptr = value;
> +		_xend();
> +	}
> +}
> +
> +static void tsx_normal(void)
> +{
> +	int value = 0;
> +
> +	if(_xbegin() == _XBEGIN_STARTED) {
> +		value++;
> +		_xend();
> +	}
> +}
> +
> +static void check_tsx_cycles(void)
> +{
> +	pmu_counter_t cnt;
> +	int i;
> +
> +	if (!this_cpu_has(X86_FEATURE_RTM) || !this_cpu_has(X86_FEATURE_HLE))
> +		return;
Since the test case is for xbegin/xend, HLE check may omit as it's for 
other X-instructions.
> +
> +	report_prefix_push("TSX cycles");
> +
> +	for (i = 0; i < pmu.nr_gp_counters; i++) {
> +		cnt.ctr = MSR_GP_COUNTERx(i);
> +
> +		if (i == 2)
> +			/* Transactional cycles commited only on gp counter 2 */
> +			cnt.config = EVNTSEL_OS | EVNTSEL_USR | 0x30000003c;
> +		else
> +			/* Transactional cycles */
> +			cnt.config = EVNTSEL_OS | EVNTSEL_USR | 0x10000003c;
> +
> +		start_event(&cnt);
> +		tsx_fault();
> +		tsx_normal();
> +		stop_event(&cnt);
> +
> +		report(cnt.count > 0, "gp cntr-%d", i);
The purpose is to collect total cycles, why not print out the data here 
for each GP counter?
> +	}
> +
> +	report_prefix_pop();
> +}
> +
>   static void check_counters(void)
>   {
>   	if (is_fep_available())
> @@ -559,6 +629,7 @@ static void check_counters(void)
>   	check_counter_overflow();
>   	check_gp_counter_cmask();
>   	check_running_counter_wrmsr();
> +	check_tsx_cycles();
>   }
>   
>   static void do_unsupported_width_counter_write(void *index)