linux-kernel - Re: [PATCH v5 11/13] KVM: selftests: Test consistency of CPUID with num of fixed counters

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Date:   Tue, 24 Oct 2023 07:22:48 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     JinrongLiang <ljr.kernel@...il.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Like Xu <likexu@...cent.com>,
        Jinrong Liang <cloudliang@...cent.com>
Subject: Re: [PATCH v5 11/13] KVM: selftests: Test consistency of CPUID with
 num of fixed counters

On Tue, Oct 24, 2023, JinrongLiang wrote:
> 在 2023/10/24 08:26, Sean Christopherson 写道:
> > From: Jinrong Liang <cloudliang@...cent.com>
> > 
> > Extend the PMU counters test to verify KVM emulation of fixed counters in
> > addition to general purpose counters.  Fixed counters add an extra wrinkle
> > in the form of an extra supported bitmask.  Thus quoth the SDM:
> > 
> >    fixed-function performance counter 'i' is supported if ECX[i] || (EDX[4:0] > i)
> > 
> > Test that KVM handles a counter being available through either method.
> > 
> > Co-developed-by: Like Xu <likexu@...cent.com>
> > Signed-off-by: Like Xu <likexu@...cent.com>
> > Signed-off-by: Jinrong Liang <cloudliang@...cent.com>
> > Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> >   .../selftests/kvm/x86_64/pmu_counters_test.c  | 58 ++++++++++++++++++-
> >   1 file changed, 55 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
> > index 274b7f4d4b53..f1d9cdd69a17 100644
> > --- a/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
> > +++ b/tools/testing/selftests/kvm/x86_64/pmu_counters_test.c
> > @@ -227,13 +227,19 @@ __GUEST_ASSERT(expect_gp ? vector == GP_VECTOR : !vector,			\
> >   	       expect_gp ? "#GP" : "no fault", msr, vector)			\
> >   static void guest_rd_wr_counters(uint32_t base_msr, uint8_t nr_possible_counters,
> > -				 uint8_t nr_counters)
> > +				 uint8_t nr_counters, uint32_t or_mask)
> >   {
> >   	uint8_t i;
> >   	for (i = 0; i < nr_possible_counters; i++) {
> >   		const uint32_t msr = base_msr + i;
> > -		const bool expect_success = i < nr_counters;
> > +
> > +		/*
> > +		 * Fixed counters are supported if the counter is less than the
> > +		 * number of enumerated contiguous counters *or* the counter is
> > +		 * explicitly enumerated in the supported counters mask.
> > +		 */
> > +		const bool expect_success = i < nr_counters || (or_mask & BIT(i));
> >   		/*
> >   		 * KVM drops writes to MSR_P6_PERFCTR[0|1] if the counters are
> > @@ -273,7 +279,7 @@ static void guest_test_gp_counters(void)
> >   	else
> >   		base_msr = MSR_IA32_PERFCTR0;
> > -	guest_rd_wr_counters(base_msr, MAX_NR_GP_COUNTERS, nr_gp_counters);
> > +	guest_rd_wr_counters(base_msr, MAX_NR_GP_COUNTERS, nr_gp_counters, 0);
> >   }
> >   static void test_gp_counters(uint8_t nr_gp_counters, uint64_t perf_cap)
> > @@ -292,10 +298,51 @@ static void test_gp_counters(uint8_t nr_gp_counters, uint64_t perf_cap)
> >   	kvm_vm_free(vm);
> >   }
> > +static void guest_test_fixed_counters(void)
> > +{
> > +	uint64_t supported_bitmask = 0;
> > +	uint8_t nr_fixed_counters = 0;
> > +
> > +	/* KVM provides fixed counters iff the vPMU version is 2+. */
> 
> s/iff/if/

The "iff" is intentional, it's shorthand for "if and only if".  Ha, it even has
a Wikipedia page: https://en.wikipedia.org/wiki/If_and_only_if.