linux-kernel - Re: [PATCH 1/1] KVM: arm64: PMU: Fix PMCR_EL0 reset value

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Date:   Mon, 12 Dec 2022 11:38:16 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Oliver Upton <oliver.upton@...ux.dev>,
        James Clark <james.clark@....com>
Cc:     kvmarm@...ts.linux.dev, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] KVM: arm64: PMU: Fix PMCR_EL0 reset value

On 12/9/22 23:28, Oliver Upton wrote:
> On Fri, Dec 09, 2022 at 04:44:46PM +0000, James Clark wrote:
>> ARMV8_PMU_PMCR_N_MASK is an unshifted value which results in the wrong
>> reset value for PMCR_EL0, so shift it to fix it.
> 
> That's just mean. *_MASK tends to be a shifted mask, although it would
> appear that asm/perf_event.h does not follow this convention. Fixing
> that would be nice (as I'm sure somebody else will get burned by this),
> but for the sake of an immediate fix:

New arch/arm64/tools/sysreg generates shifted i.e in place masks for register
fields. Once all these PMU registers move into arch/arm64/tools/sysreg, this
problem will be solved.

> 
>> This fixes the following error when running qemu:
>>
>>   $ qemu-system-aarch64 -cpu host -machine type=virt,accel=kvm -kernel ...
>>
>>   target/arm/helper.c:1813: pmevcntr_rawwrite: Assertion `counter < pmu_num_counters(env)' failed.
>>
>> Fixes: 292e8f149476 ("KVM: arm64: PMU: Simplify PMCR_EL0 reset handling")
>> Signed-off-by: James Clark <james.clark@....com>
> 
> Reviewed-by: Oliver Upton <oliver.upton@...ux.dev>
> 
> --
> Thanks,
> Oliver
> 
>> ---
>>  arch/arm64/kvm/sys_regs.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index d5ee52d6bf73..c6cbfe6b854b 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -646,7 +646,7 @@ static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>>  		return;
>>  
>>  	/* Only preserve PMCR_EL0.N, and reset the rest to 0 */
>> -	pmcr = read_sysreg(pmcr_el0) & ARMV8_PMU_PMCR_N_MASK;
>> +	pmcr = read_sysreg(pmcr_el0) & (ARMV8_PMU_PMCR_N_MASK << ARMV8_PMU_PMCR_N_SHIFT);
>>  	if (!kvm_supports_32bit_el0())
>>  		pmcr |= ARMV8_PMU_PMCR_LC;
>>  
>> -- 
>> 2.25.1
>>
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

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