Re: [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements

From: Marc Zyngier <maz@kernel.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
	kvmarm@lists.cs.columbia.edu, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandre Chartre <alexandre.chartre@oracle.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Andrew Jones <drjones@redhat.com>,
	Russell King <linux@arm.linux.org.uk>,
	kernel-team@android.com,
	Russell King <rmk+kernel@armlinux.org.uk>
Subject: Re: [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
Date: Mon, 19 Jul 2021 16:56:34 +0100	[thread overview]
Message-ID: <171834f3198b898d5c2aefa0270b65f2@kernel.org> (raw)
In-Reply-To: <171cca9d-2a6e-248c-8502-feba8ebbe55e@arm.com>

On 2021-07-19 16:55, Alexandru Elisei wrote:
> Hi Marc,
> 
> On 7/19/21 1:38 PM, Marc Zyngier wrote:
>> A number of the PMU sysregs expose reset values that are not
>> compliant with the architecture (set bits in the RES0 ranges,
>> for example).
>> 
>> This in turn has the effect that we need to pointlessly mask
>> some register fields when using them.
>> 
>> Let's start by making sure we don't have illegal values in the
>> shadow registers at reset time. This affects all the registers
>> that dedicate one bit per counter, the counters themselves,
>> PMEVTYPERn_EL0 and PMSELR_EL0.
>> 
>> Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>>  arch/arm64/kvm/sys_regs.c | 43 
>> ++++++++++++++++++++++++++++++++++++---
>>  1 file changed, 40 insertions(+), 3 deletions(-)
>> 
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index f6f126eb6ac1..96bdfa0e68b2 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -603,6 +603,41 @@ static unsigned int pmu_visibility(const struct 
>> kvm_vcpu *vcpu,
>>  	return REG_HIDDEN;
>>  }
>> 
>> +static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct 
>> sys_reg_desc *r)
>> +{
>> +	u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
>> +
>> +	/* No PMU available, any PMU reg may UNDEF... */
>> +	if (!kvm_arm_support_pmu_v3())
>> +		return;
>> +
>> +	n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
>> +	n &= ARMV8_PMU_PMCR_N_MASK;
>> +	if (n)
>> +		mask |= GENMASK(n - 1, 0);
> 
> Hm... seems to be missing the cycle counter.

Check the declaration for 'mask'... :-)

         M.
-- 
Jazz is not dead. It just smells funny...

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