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    SubjectRe: [PATCH v8 05/13] KVM: arm64: Add {get,set}_user for PM{C,I}NTEN{SET,CLR}, PMOVS{SET,CLR}
    On Mon, Oct 23, 2023 at 5:31 AM Marc Zyngier <maz@kernel.org> wrote:
    >
    > 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 },
    >

    Thanks for the suggestion. I'll consider this in the next iteration.

    - Raghavendra

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