Re: [PATCH v8 05/13] KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
From: Raghavendra Rao Ananta
Date: Mon Oct 23 2023 - 13:29:06 EST
On Mon, Oct 23, 2023 at 5:31 AM Marc Zyngier <maz@xxxxxxxxxx> wrote:
>
> On Fri, 20 Oct 2023 22:40:45 +0100,
> Raghavendra Rao Ananta <rananta@xxxxxxxxxx> 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@xxxxxxxxxx>
> > ---
> > 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 },
>
Thanks for the suggestion. I'll consider this in the next iteration.
- Raghavendra