Re: [PATCH v8 04/20] KVM: ARM64: Add access handler for PMCR register

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

On 22/12/15 08:07, 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 except PMCR.E which is zero. Add an access
> handler for PMCR.
> 
> Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 39 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 37 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index e8bf374..c60047e 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -34,6 +34,7 @@
>  #include <asm/kvm_emulate.h>
>  #include <asm/kvm_host.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/pmu.h>
>  
>  #include <trace/events/kvm.h>
>  
> @@ -439,6 +440,40 @@ 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)
> +{
> +	u64 pmcr, val;
> +
> +	asm volatile("mrs %0, pmcr_el0\n" : "=r" (pmcr));
> +	/* Writable bits of PMCR_EL0 (ARMV8_PMCR_MASK) is reset to UNKNOWN
> +	 * except PMCR.E resetting to zero.
> +	 */
> +	val = ((pmcr & ~ARMV8_PMCR_MASK) | (ARMV8_PMCR_MASK & 0xdecafbad))
> +	      & (~ARMV8_PMCR_E);
> +	vcpu_sys_reg(vcpu, r->reg) = val;
> +}
> +
> +static bool access_pmcr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> +			const struct sys_reg_desc *r)
> +{
> +	u64 val;
> +
> +	if (p->is_write) {
> +		/* Only update writeable bits of PMCR */
> +		val = vcpu_sys_reg(vcpu, r->reg);
> +		val &= ~ARMV8_PMCR_MASK;
> +		val |= p->regval & ARMV8_PMCR_MASK;
> +		vcpu_sys_reg(vcpu, r->reg) = val;
> +	} else {
> +		/* PMCR.P & PMCR.C are RAZ */
> +		val = vcpu_sys_reg(vcpu, r->reg)
> +		      & ~(ARMV8_PMCR_P | ARMV8_PMCR_C);
> +		p->regval = val;
> +	}

How can that work for 32bit, where r->reg is not populated from the trap
table? You *know* that you are accessing PMCR, so just use PMCR_EL0 as
an index into vcpu_sys_reg() in all cases. You can then drop PMCR_EL0
from the 64bit trap table entry.

> +
> +	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 */						\
> @@ -623,7 +658,7 @@ 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_pmcr, reset_pmcr, PMCR_EL0, },
>  	/* PMCNTENSET_EL0 */
>  	{ Op0(0b11), Op1(0b011), CRn(0b1001), CRm(0b1100), Op2(0b001),
>  	  trap_raz_wi },
> @@ -885,7 +920,7 @@ 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_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 },
> 

Thanks,

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