Re: [PATCH v2 04/22] KVM: ARM64: Add reset and access handlers for PMCR_EL0 register

[Marc Zyngier <marc.zyngier@arm.com>]

On 11/09/15 09:54, Shannon Zhao wrote:
> From: Shannon Zhao <shannon.zhao@linaro.org>
> 
> Add reset handler which gets host value of PMCR_EL0 and make writable
> bits architecturally UNKNOWN. Add a common access handler for PMU
> registers which emulates writing and reading register and add emulation
> for PMCR.
> 
> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 76 +++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 74 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index c370b40..db1be44 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -33,6 +33,7 @@
>  #include <asm/kvm_emulate.h>
>  #include <asm/kvm_host.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/pmu.h>
>  
>  #include <trace/events/kvm.h>
>  
> @@ -236,6 +237,48 @@ static void reset_mpidr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>  	vcpu_sys_reg(vcpu, MPIDR_EL1) = (1ULL << 31) | mpidr;
>  }
>  
> +static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> +{
> +	u32 pmcr;
> +
> +	asm volatile("mrs %0, pmcr_el0\n" : "=r" (pmcr));
> +	/* Writable bits of PMCR_EL0 (ARMV8_PMCR_MASK) is reset to UNKNOWN*/
> +	if (!vcpu_mode_is_32bit(vcpu))
> +		vcpu_sys_reg(vcpu, r->reg) = (pmcr & ~ARMV8_PMCR_MASK)
> +					     | (ARMV8_PMCR_MASK & 0xdecafbad);
> +	else
> +		vcpu_cp15(vcpu, r->reg) = (pmcr & ~ARMV8_PMCR_MASK)
> +					  | (ARMV8_PMCR_MASK & 0xdecafbad);

I have some concerns about blindly reusing the top bits of the host's
PMCR_EL0 register, specially when it comes to the PMCR_EL0.N. Given that
we're fully emulating the PMU, shouldn't we simply define how many
counters we're emulating?

> +}
> +
> +/* PMU registers accessor. */
> +static bool access_pmu_regs(struct kvm_vcpu *vcpu,
> +			    const struct sys_reg_params *p,
> +			    const struct sys_reg_desc *r)
> +{
> +	unsigned long val;
> +
> +	if (p->is_write) {
> +		switch (r->reg) {
> +		case PMCR_EL0: {
> +			/* Only update writeable bits of PMCR */
> +			val = vcpu_sys_reg(vcpu, r->reg);
> +			val &= ~ARMV8_PMCR_MASK;
> +			val |= *vcpu_reg(vcpu, p->Rt) & ARMV8_PMCR_MASK;
> +			vcpu_sys_reg(vcpu, r->reg) = val;
> +			break;
> +		}
> +		default:
> +			vcpu_sys_reg(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
> +			break;
> +		}
> +	} else {
> +		*vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, r->reg);
> +	}
> +
> +	return true;
> +}
> +
>  /* Silly macro to expand the DBG{BCR,BVR,WVR,WCR}n_EL1 registers in one go */
>  #define DBG_BCR_BVR_WCR_WVR_EL1(n)					\
>  	/* DBGBVRn_EL1 */						\
> @@ -427,7 +470,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  
>  	/* PMCR_EL0 */
>  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b000),
> -	  trap_raz_wi },
> +	  access_pmu_regs, reset_pmcr, PMCR_EL0, },
>  	/* PMCNTENSET_EL0 */
>  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b001),
>  	  trap_raz_wi },
> @@ -632,6 +675,34 @@ static const struct sys_reg_desc cp14_64_regs[] = {
>  	{ Op1( 0), CRm( 2), .access = trap_raz_wi },
>  };
>  
> +/* PMU CP15 registers accessor. */
> +static bool access_pmu_cp15_regs(struct kvm_vcpu *vcpu,
> +				 const struct sys_reg_params *p,
> +				 const struct sys_reg_desc *r)
> +{
> +	unsigned long val;
> +
> +	if (p->is_write) {
> +		switch (r->reg) {
> +		case c9_PMCR: {
> +			/* Only update writeable bits of PMCR */
> +			val = vcpu_cp15(vcpu, r->reg);
> +			val &= ~ARMV8_PMCR_MASK;
> +			val |= *vcpu_reg(vcpu, p->Rt) & ARMV8_PMCR_MASK;
> +			vcpu_cp15(vcpu, r->reg) = val;
> +			break;
> +		}
> +		default:
> +			vcpu_cp15(vcpu, r->reg) = *vcpu_reg(vcpu, p->Rt);
> +			break;
> +		}
> +	} else {
> +		*vcpu_reg(vcpu, p->Rt) = vcpu_cp15(vcpu, r->reg);
> +	}
> +
> +	return true;
> +}
> +
>  /*
>   * Trapped cp15 registers. TTBR0/TTBR1 get a double encoding,
>   * depending on the way they are accessed (as a 32bit or a 64bit
> @@ -660,7 +731,8 @@ static const struct sys_reg_desc cp15_regs[] = {
>  	{ Op1( 0), CRn( 7), CRm(14), Op2( 2), access_dcsw },
>  
>  	/* PMU */
> -	{ Op1( 0), CRn( 9), CRm(12), Op2( 0), trap_raz_wi },
> +	{ Op1( 0), CRn( 9), CRm(12), Op2( 0), access_pmu_cp15_regs,
> +	  reset_pmcr, c9_PMCR },
>  	{ Op1( 0), CRn( 9), CRm(12), Op2( 1), trap_raz_wi },
>  	{ Op1( 0), CRn( 9), CRm(12), Op2( 2), trap_raz_wi },
>  	{ Op1( 0), CRn( 9), CRm(12), Op2( 3), trap_raz_wi },
> 


-- 
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