Re: [PATCH v8 05/13] KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}

From: Marc Zyngier <maz@kernel.org>
To: Raghavendra Rao Ananta <rananta@google.com>
Cc: Oliver Upton <oliver.upton@linux.dev>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Shaoqin Huang <shahuang@redhat.com>,
	Jing Zhang <jingzhangos@google.com>,
	Reiji Watanabe <reijiw@google.com>,
	Colton Lewis <coltonlewis@google.com>,
	linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v8 05/13] KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
Date: Mon, 23 Oct 2023 13:31:15 +0100	[thread overview]
Message-ID: <86zg094j1o.wl-maz@kernel.org> (raw)
In-Reply-To: <20231020214053.2144305-6-rananta@google.com>

On Fri, 20 Oct 2023 22:40:45 +0100,
Raghavendra Rao Ananta <rananta@google.com> wrote:
> 
> For unimplemented counters, the bits in PM{C,I}NTEN{SET,CLR} and
> PMOVS{SET,CLR} registers are expected to RAZ. To honor this,
> explicitly implement the {get,set}_user functions for these
> registers to mask out unimplemented counters for userspace reads
> and writes.
> 
> Signed-off-by: Raghavendra Rao Ananta <rananta@google.com>
> ---
>  arch/arm64/kvm/sys_regs.c | 91 ++++++++++++++++++++++++++++++++++++---
>  1 file changed, 85 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index faf97878dfbbb..2e5d497596ef8 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -987,6 +987,45 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>  	return true;
>  }
>  
> +static void set_pmreg_for_valid_counters(struct kvm_vcpu *vcpu,
> +					  u64 reg, u64 val, bool set)
> +{
> +	struct kvm *kvm = vcpu->kvm;
> +
> +	mutex_lock(&kvm->arch.config_lock);
> +
> +	/* Make the register immutable once the VM has started running */
> +	if (kvm_vm_has_ran_once(kvm)) {
> +		mutex_unlock(&kvm->arch.config_lock);
> +		return;
> +	}
> +
> +	val &= kvm_pmu_valid_counter_mask(vcpu);
> +	mutex_unlock(&kvm->arch.config_lock);
> +
> +	if (set)
> +		__vcpu_sys_reg(vcpu, reg) |= val;
> +	else
> +		__vcpu_sys_reg(vcpu, reg) &= ~val;
> +}
> +
> +static int get_pmcnten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
> +			u64 *val)
> +{
> +	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
> +
> +	*val = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
> +	return 0;
> +}
> +
> +static int set_pmcnten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
> +			u64 val)
> +{
> +	/* r->Op2 & 0x1: true for PMCNTENSET_EL0, else PMCNTENCLR_EL0 */
> +	set_pmreg_for_valid_counters(vcpu, PMCNTENSET_EL0, val, r->Op2 & 0x1);
> +	return 0;
> +}

Huh, this is really ugly. Why the explosion of pointless helpers when
the whole design of the sysreg infrastructure to have *common* helpers
for registers that behave the same way?

I'd expect something like the hack below instead.

	M.

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index a2c5f210b3d6..8f560a2496f2 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -987,42 +987,46 @@ static bool access_pmu_evtyper(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	return true;
 }
 
-static void set_pmreg_for_valid_counters(struct kvm_vcpu *vcpu,
-					  u64 reg, u64 val, bool set)
+static int set_pmreg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, u64 val)
 {
 	struct kvm *kvm = vcpu->kvm;
+	bool set;
 
 	mutex_lock(&kvm->arch.config_lock);
 
 	/* Make the register immutable once the VM has started running */
 	if (kvm_vm_has_ran_once(kvm)) {
 		mutex_unlock(&kvm->arch.config_lock);
-		return;
+		return 0;
 	}
 
 	val &= kvm_pmu_valid_counter_mask(vcpu);
 	mutex_unlock(&kvm->arch.config_lock);
 
+	switch(r->reg) {
+	case PMOVSSET_EL0:
+		/* CRm[1] being set indicates a SET register, and CLR otherwise */
+	        set = r->CRm & 2;
+		break;
+	default:
+		/* Op2[0] being set indicates a SET register, and CLR otherwise */
+	        set = r->Op2 & 1;
+		break;
+	}
+
 	if (set)
-		__vcpu_sys_reg(vcpu, reg) |= val;
+		__vcpu_sys_reg(vcpu, r->reg) |= val;
 	else
-		__vcpu_sys_reg(vcpu, reg) &= ~val;
-}
-
-static int get_pmcnten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-			u64 *val)
-{
-	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
+		__vcpu_sys_reg(vcpu, r->reg) &= ~val;
 
-	*val = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
 	return 0;
 }
 
-static int set_pmcnten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-			u64 val)
+static int get_pmreg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r, u64 *val)
 {
-	/* r->Op2 & 0x1: true for PMCNTENSET_EL0, else PMCNTENCLR_EL0 */
-	set_pmreg_for_valid_counters(vcpu, PMCNTENSET_EL0, val, r->Op2 & 0x1);
+	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
+
+	*val = __vcpu_sys_reg(vcpu, r->reg) & mask;
 	return 0;
 }
 
@@ -1054,23 +1058,6 @@ static bool access_pmcnten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	return true;
 }
 
-static int get_pminten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-			u64 *val)
-{
-	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
-
-	*val = __vcpu_sys_reg(vcpu, PMINTENSET_EL1) & mask;
-	return 0;
-}
-
-static int set_pminten(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-			u64 val)
-{
-	/* r->Op2 & 0x1: true for PMINTENSET_EL1, else PMINTENCLR_EL1 */
-	set_pmreg_for_valid_counters(vcpu, PMINTENSET_EL1, val, r->Op2 & 0x1);
-	return 0;
-}
-
 static bool access_pminten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 			   const struct sys_reg_desc *r)
 {
@@ -1095,23 +1082,6 @@ static bool access_pminten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 	return true;
 }
 
-static int set_pmovs(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-		      u64 val)
-{
-	/* r->CRm & 0x2: true for PMOVSSET_EL0, else PMOVSCLR_EL0 */
-	set_pmreg_for_valid_counters(vcpu, PMOVSSET_EL0, val, r->CRm & 0x2);
-	return 0;
-}
-
-static int get_pmovs(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r,
-		      u64 *val)
-{
-	u64 mask = kvm_pmu_valid_counter_mask(vcpu);
-
-	*val = __vcpu_sys_reg(vcpu, PMOVSSET_EL0) & mask;
-	return 0;
-}
-
 static bool access_pmovs(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
 			 const struct sys_reg_desc *r)
 {
@@ -2311,10 +2281,10 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 
 	{ PMU_SYS_REG(PMINTENSET_EL1),
 	  .access = access_pminten, .reg = PMINTENSET_EL1,
-	  .get_user = get_pminten, .set_user = set_pminten },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 	{ PMU_SYS_REG(PMINTENCLR_EL1),
 	  .access = access_pminten, .reg = PMINTENSET_EL1,
-	  .get_user = get_pminten, .set_user = set_pminten },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 	{ SYS_DESC(SYS_PMMIR_EL1), trap_raz_wi },
 
 	{ SYS_DESC(SYS_MAIR_EL1), access_vm_reg, reset_unknown, MAIR_EL1 },
@@ -2366,13 +2336,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	  .reg = PMCR_EL0, .get_user = get_pmcr, .set_user = set_pmcr },
 	{ PMU_SYS_REG(PMCNTENSET_EL0),
 	  .access = access_pmcnten, .reg = PMCNTENSET_EL0,
-	  .get_user = get_pmcnten, .set_user = set_pmcnten },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 	{ PMU_SYS_REG(PMCNTENCLR_EL0),
 	  .access = access_pmcnten, .reg = PMCNTENSET_EL0,
-	  .get_user = get_pmcnten, .set_user = set_pmcnten },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 	{ PMU_SYS_REG(PMOVSCLR_EL0),
 	  .access = access_pmovs, .reg = PMOVSSET_EL0,
-	  .get_user = get_pmovs, .set_user = set_pmovs },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 	/*
 	 * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
 	 * previously (and pointlessly) advertised in the past...
@@ -2401,7 +2371,7 @@ static const struct sys_reg_desc sys_reg_descs[] = {
 	  .reset = reset_val, .reg = PMUSERENR_EL0, .val = 0 },
 	{ PMU_SYS_REG(PMOVSSET_EL0),
 	  .access = access_pmovs, .reg = PMOVSSET_EL0,
-	  .get_user = get_pmovs, .set_user = set_pmovs },
+	  .get_user = get_pmreg, .set_user = set_pmreg },
 
 	{ SYS_DESC(SYS_TPIDR_EL0), NULL, reset_unknown, TPIDR_EL0 },
 	{ SYS_DESC(SYS_TPIDRRO_EL0), NULL, reset_unknown, TPIDRRO_EL0 },

-- 
Without deviation from the norm, progress is not possible.
