* [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
2021-07-19 12:38 [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
@ 2021-07-19 12:38 ` Marc Zyngier
2021-07-19 15:55 ` Alexandru Elisei
2021-07-19 12:39 ` [PATCH v2 2/4] KVM: arm64: Drop unnecessary masking of PMU registers Marc Zyngier
` (3 subsequent siblings)
4 siblings, 1 reply; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 12:38 UTC (permalink / raw)
To: linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandru Elisei,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team, Russell King
A number of the PMU sysregs expose reset values that are not
compliant with the architecture (set bits in the RES0 ranges,
for example).
This in turn has the effect that we need to pointlessly mask
some register fields when using them.
Let's start by making sure we don't have illegal values in the
shadow registers at reset time. This affects all the registers
that dedicate one bit per counter, the counters themselves,
PMEVTYPERn_EL0 and PMSELR_EL0.
Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/sys_regs.c | 43 ++++++++++++++++++++++++++++++++++++---
1 file changed, 40 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index f6f126eb6ac1..96bdfa0e68b2 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -603,6 +603,41 @@ static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
return REG_HIDDEN;
}
+static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+ u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
+
+ /* No PMU available, any PMU reg may UNDEF... */
+ if (!kvm_arm_support_pmu_v3())
+ return;
+
+ n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
+ n &= ARMV8_PMU_PMCR_N_MASK;
+ if (n)
+ mask |= GENMASK(n - 1, 0);
+
+ reset_unknown(vcpu, r);
+ __vcpu_sys_reg(vcpu, r->reg) &= mask;
+}
+
+static void reset_pmevcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+ reset_unknown(vcpu, r);
+ __vcpu_sys_reg(vcpu, r->reg) &= GENMASK(31, 0);
+}
+
+static void reset_pmevtyper(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+ reset_unknown(vcpu, r);
+ __vcpu_sys_reg(vcpu, r->reg) &= ARMV8_PMU_EVTYPE_MASK;
+}
+
+static void reset_pmselr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
+{
+ reset_unknown(vcpu, r);
+ __vcpu_sys_reg(vcpu, r->reg) &= ARMV8_PMU_COUNTER_MASK;
+}
+
static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
{
u64 pmcr, val;
@@ -944,16 +979,18 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
trap_wcr, reset_wcr, 0, 0, get_wcr, set_wcr }
#define PMU_SYS_REG(r) \
- SYS_DESC(r), .reset = reset_unknown, .visibility = pmu_visibility
+ SYS_DESC(r), .reset = reset_pmu_reg, .visibility = pmu_visibility
/* Macro to expand the PMEVCNTRn_EL0 register */
#define PMU_PMEVCNTR_EL0(n) \
{ PMU_SYS_REG(SYS_PMEVCNTRn_EL0(n)), \
+ .reset = reset_pmevcntr, \
.access = access_pmu_evcntr, .reg = (PMEVCNTR0_EL0 + n), }
/* Macro to expand the PMEVTYPERn_EL0 register */
#define PMU_PMEVTYPER_EL0(n) \
{ PMU_SYS_REG(SYS_PMEVTYPERn_EL0(n)), \
+ .reset = reset_pmevtyper, \
.access = access_pmu_evtyper, .reg = (PMEVTYPER0_EL0 + n), }
static bool undef_access(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
@@ -1595,13 +1632,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
{ PMU_SYS_REG(SYS_PMSWINC_EL0),
.access = access_pmswinc, .reg = PMSWINC_EL0 },
{ PMU_SYS_REG(SYS_PMSELR_EL0),
- .access = access_pmselr, .reg = PMSELR_EL0 },
+ .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 },
{ PMU_SYS_REG(SYS_PMCEID0_EL0),
.access = access_pmceid, .reset = NULL },
{ PMU_SYS_REG(SYS_PMCEID1_EL0),
.access = access_pmceid, .reset = NULL },
{ PMU_SYS_REG(SYS_PMCCNTR_EL0),
- .access = access_pmu_evcntr, .reg = PMCCNTR_EL0 },
+ .access = access_pmu_evcntr, .reset = reset_unknown, .reg = PMCCNTR_EL0 },
{ PMU_SYS_REG(SYS_PMXEVTYPER_EL0),
.access = access_pmu_evtyper, .reset = NULL },
{ PMU_SYS_REG(SYS_PMXEVCNTR_EL0),
--
2.30.2
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^ permalink raw reply related [flat|nested] 13+ messages in thread* Re: [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
2021-07-19 12:38 ` [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements Marc Zyngier
@ 2021-07-19 15:55 ` Alexandru Elisei
2021-07-19 15:56 ` Marc Zyngier
0 siblings, 1 reply; 13+ messages in thread
From: Alexandru Elisei @ 2021-07-19 15:55 UTC (permalink / raw)
To: Marc Zyngier, linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandre Chartre, Robin Murphy,
Andrew Jones, Russell King, kernel-team, Russell King
Hi Marc,
On 7/19/21 1:38 PM, Marc Zyngier wrote:
> A number of the PMU sysregs expose reset values that are not
> compliant with the architecture (set bits in the RES0 ranges,
> for example).
>
> This in turn has the effect that we need to pointlessly mask
> some register fields when using them.
>
> Let's start by making sure we don't have illegal values in the
> shadow registers at reset time. This affects all the registers
> that dedicate one bit per counter, the counters themselves,
> PMEVTYPERn_EL0 and PMSELR_EL0.
>
> Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/kvm/sys_regs.c | 43 ++++++++++++++++++++++++++++++++++++---
> 1 file changed, 40 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index f6f126eb6ac1..96bdfa0e68b2 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -603,6 +603,41 @@ static unsigned int pmu_visibility(const struct kvm_vcpu *vcpu,
> return REG_HIDDEN;
> }
>
> +static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> +{
> + u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
> +
> + /* No PMU available, any PMU reg may UNDEF... */
> + if (!kvm_arm_support_pmu_v3())
> + return;
> +
> + n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
> + n &= ARMV8_PMU_PMCR_N_MASK;
> + if (n)
> + mask |= GENMASK(n - 1, 0);
Hm... seems to be missing the cycle counter.
Thanks,
Alex
> +
> + reset_unknown(vcpu, r);
> + __vcpu_sys_reg(vcpu, r->reg) &= mask;
> +}
> +
> +static void reset_pmevcntr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> +{
> + reset_unknown(vcpu, r);
> + __vcpu_sys_reg(vcpu, r->reg) &= GENMASK(31, 0);
> +}
> +
> +static void reset_pmevtyper(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> +{
> + reset_unknown(vcpu, r);
> + __vcpu_sys_reg(vcpu, r->reg) &= ARMV8_PMU_EVTYPE_MASK;
> +}
> +
> +static void reset_pmselr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> +{
> + reset_unknown(vcpu, r);
> + __vcpu_sys_reg(vcpu, r->reg) &= ARMV8_PMU_COUNTER_MASK;
> +}
> +
> static void reset_pmcr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
> {
> u64 pmcr, val;
> @@ -944,16 +979,18 @@ static bool access_pmuserenr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> trap_wcr, reset_wcr, 0, 0, get_wcr, set_wcr }
>
> #define PMU_SYS_REG(r) \
> - SYS_DESC(r), .reset = reset_unknown, .visibility = pmu_visibility
> + SYS_DESC(r), .reset = reset_pmu_reg, .visibility = pmu_visibility
>
> /* Macro to expand the PMEVCNTRn_EL0 register */
> #define PMU_PMEVCNTR_EL0(n) \
> { PMU_SYS_REG(SYS_PMEVCNTRn_EL0(n)), \
> + .reset = reset_pmevcntr, \
> .access = access_pmu_evcntr, .reg = (PMEVCNTR0_EL0 + n), }
>
> /* Macro to expand the PMEVTYPERn_EL0 register */
> #define PMU_PMEVTYPER_EL0(n) \
> { PMU_SYS_REG(SYS_PMEVTYPERn_EL0(n)), \
> + .reset = reset_pmevtyper, \
> .access = access_pmu_evtyper, .reg = (PMEVTYPER0_EL0 + n), }
>
> static bool undef_access(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> @@ -1595,13 +1632,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> { PMU_SYS_REG(SYS_PMSWINC_EL0),
> .access = access_pmswinc, .reg = PMSWINC_EL0 },
> { PMU_SYS_REG(SYS_PMSELR_EL0),
> - .access = access_pmselr, .reg = PMSELR_EL0 },
> + .access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 },
> { PMU_SYS_REG(SYS_PMCEID0_EL0),
> .access = access_pmceid, .reset = NULL },
> { PMU_SYS_REG(SYS_PMCEID1_EL0),
> .access = access_pmceid, .reset = NULL },
> { PMU_SYS_REG(SYS_PMCCNTR_EL0),
> - .access = access_pmu_evcntr, .reg = PMCCNTR_EL0 },
> + .access = access_pmu_evcntr, .reset = reset_unknown, .reg = PMCCNTR_EL0 },
> { PMU_SYS_REG(SYS_PMXEVTYPER_EL0),
> .access = access_pmu_evtyper, .reset = NULL },
> { PMU_SYS_REG(SYS_PMXEVCNTR_EL0),
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^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
2021-07-19 15:55 ` Alexandru Elisei
@ 2021-07-19 15:56 ` Marc Zyngier
2021-07-19 16:02 ` Alexandru Elisei
0 siblings, 1 reply; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 15:56 UTC (permalink / raw)
To: Alexandru Elisei
Cc: linux-arm-kernel, kvm, kvmarm, James Morse, Suzuki K Poulose,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team, Russell King
On 2021-07-19 16:55, Alexandru Elisei wrote:
> Hi Marc,
>
> On 7/19/21 1:38 PM, Marc Zyngier wrote:
>> A number of the PMU sysregs expose reset values that are not
>> compliant with the architecture (set bits in the RES0 ranges,
>> for example).
>>
>> This in turn has the effect that we need to pointlessly mask
>> some register fields when using them.
>>
>> Let's start by making sure we don't have illegal values in the
>> shadow registers at reset time. This affects all the registers
>> that dedicate one bit per counter, the counters themselves,
>> PMEVTYPERn_EL0 and PMSELR_EL0.
>>
>> Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>> arch/arm64/kvm/sys_regs.c | 43
>> ++++++++++++++++++++++++++++++++++++---
>> 1 file changed, 40 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index f6f126eb6ac1..96bdfa0e68b2 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -603,6 +603,41 @@ static unsigned int pmu_visibility(const struct
>> kvm_vcpu *vcpu,
>> return REG_HIDDEN;
>> }
>>
>> +static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct
>> sys_reg_desc *r)
>> +{
>> + u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
>> +
>> + /* No PMU available, any PMU reg may UNDEF... */
>> + if (!kvm_arm_support_pmu_v3())
>> + return;
>> +
>> + n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
>> + n &= ARMV8_PMU_PMCR_N_MASK;
>> + if (n)
>> + mask |= GENMASK(n - 1, 0);
>
> Hm... seems to be missing the cycle counter.
Check the declaration for 'mask'... :-)
M.
--
Jazz is not dead. It just smells funny...
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^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
2021-07-19 15:56 ` Marc Zyngier
@ 2021-07-19 16:02 ` Alexandru Elisei
0 siblings, 0 replies; 13+ messages in thread
From: Alexandru Elisei @ 2021-07-19 16:02 UTC (permalink / raw)
To: Marc Zyngier
Cc: linux-arm-kernel, kvm, kvmarm, James Morse, Suzuki K Poulose,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team, Russell King
Hi Marc,
On 7/19/21 4:56 PM, Marc Zyngier wrote:
> On 2021-07-19 16:55, Alexandru Elisei wrote:
>> Hi Marc,
>>
>> On 7/19/21 1:38 PM, Marc Zyngier wrote:
>>> A number of the PMU sysregs expose reset values that are not
>>> compliant with the architecture (set bits in the RES0 ranges,
>>> for example).
>>>
>>> This in turn has the effect that we need to pointlessly mask
>>> some register fields when using them.
>>>
>>> Let's start by making sure we don't have illegal values in the
>>> shadow registers at reset time. This affects all the registers
>>> that dedicate one bit per counter, the counters themselves,
>>> PMEVTYPERn_EL0 and PMSELR_EL0.
>>>
>>> Reported-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>>> Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
>>> Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>> arch/arm64/kvm/sys_regs.c | 43 ++++++++++++++++++++++++++++++++++++---
>>> 1 file changed, 40 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>> index f6f126eb6ac1..96bdfa0e68b2 100644
>>> --- a/arch/arm64/kvm/sys_regs.c
>>> +++ b/arch/arm64/kvm/sys_regs.c
>>> @@ -603,6 +603,41 @@ static unsigned int pmu_visibility(const struct kvm_vcpu
>>> *vcpu,
>>> return REG_HIDDEN;
>>> }
>>>
>>> +static void reset_pmu_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>>> +{
>>> + u64 n, mask = BIT(ARMV8_PMU_CYCLE_IDX);
>>> +
>>> + /* No PMU available, any PMU reg may UNDEF... */
>>> + if (!kvm_arm_support_pmu_v3())
>>> + return;
>>> +
>>> + n = read_sysreg(pmcr_el0) >> ARMV8_PMU_PMCR_N_SHIFT;
>>> + n &= ARMV8_PMU_PMCR_N_MASK;
>>> + if (n)
>>> + mask |= GENMASK(n - 1, 0);
>>
>> Hm... seems to be missing the cycle counter.
>
> Check the declaration for 'mask'... :-)
Yeah, sorry for that, I still had in my mind the original function body.
Everything looks alright to me, no changes from the previous version (PMSWINC_EL1
is handled in the last patch) where I had checked that the reset values match the
architecture:
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Thanks,
Alex
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^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH v2 2/4] KVM: arm64: Drop unnecessary masking of PMU registers
2021-07-19 12:38 [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
2021-07-19 12:38 ` [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements Marc Zyngier
@ 2021-07-19 12:39 ` Marc Zyngier
2021-07-19 12:39 ` [PATCH v2 3/4] KVM: arm64: Disabling disabled PMU counters wastes a lot of time Marc Zyngier
` (2 subsequent siblings)
4 siblings, 0 replies; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 12:39 UTC (permalink / raw)
To: linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandru Elisei,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team, Russell King
We always sanitise our PMU sysreg on the write side, so there
is no need to do it on the read side as well.
Drop the unnecessary masking.
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/kvm/pmu-emul.c | 3 +--
arch/arm64/kvm/sys_regs.c | 6 +++---
2 files changed, 4 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index f33825c995cb..fae4e95b586c 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -373,7 +373,6 @@ static u64 kvm_pmu_overflow_status(struct kvm_vcpu *vcpu)
reg = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
reg &= __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
reg &= __vcpu_sys_reg(vcpu, PMINTENSET_EL1);
- reg &= kvm_pmu_valid_counter_mask(vcpu);
}
return reg;
@@ -569,7 +568,7 @@ void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
if (val & ARMV8_PMU_PMCR_E) {
kvm_pmu_enable_counter_mask(vcpu,
- __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask);
+ __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
} else {
kvm_pmu_disable_counter_mask(vcpu, mask);
}
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 96bdfa0e68b2..f22139658e48 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -880,7 +880,7 @@ static bool access_pmcnten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
kvm_pmu_disable_counter_mask(vcpu, val);
}
} else {
- p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0) & mask;
+ p->regval = __vcpu_sys_reg(vcpu, PMCNTENSET_EL0);
}
return true;
@@ -904,7 +904,7 @@ static bool access_pminten(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
/* accessing PMINTENCLR_EL1 */
__vcpu_sys_reg(vcpu, PMINTENSET_EL1) &= ~val;
} else {
- p->regval = __vcpu_sys_reg(vcpu, PMINTENSET_EL1) & mask;
+ p->regval = __vcpu_sys_reg(vcpu, PMINTENSET_EL1);
}
return true;
@@ -926,7 +926,7 @@ static bool access_pmovs(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
/* accessing PMOVSCLR_EL0 */
__vcpu_sys_reg(vcpu, PMOVSSET_EL0) &= ~(p->regval & mask);
} else {
- p->regval = __vcpu_sys_reg(vcpu, PMOVSSET_EL0) & mask;
+ p->regval = __vcpu_sys_reg(vcpu, PMOVSSET_EL0);
}
return true;
--
2.30.2
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^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v2 3/4] KVM: arm64: Disabling disabled PMU counters wastes a lot of time
2021-07-19 12:38 [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
2021-07-19 12:38 ` [PATCH v2 1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements Marc Zyngier
2021-07-19 12:39 ` [PATCH v2 2/4] KVM: arm64: Drop unnecessary masking of PMU registers Marc Zyngier
@ 2021-07-19 12:39 ` Marc Zyngier
2021-07-19 12:39 ` [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register Marc Zyngier
2021-08-02 13:39 ` [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
4 siblings, 0 replies; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 12:39 UTC (permalink / raw)
To: linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandru Elisei,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team, Russell King
From: Alexandre Chartre <alexandre.chartre@oracle.com>
In a KVM guest on arm64, performance counters interrupts have an
unnecessary overhead which slows down execution when using the "perf
record" command and limits the "perf record" sampling period.
The problem is that when a guest VM disables counters by clearing the
PMCR_EL0.E bit (bit 0), KVM will disable all counters defined in
PMCR_EL0 even if they are not enabled in PMCNTENSET_EL0.
KVM disables a counter by calling into the perf framework, in particular
by calling perf_event_create_kernel_counter() which is a time consuming
operation. So, for example, with a Neoverse N1 CPU core which has 6 event
counters and one cycle counter, KVM will always disable all 7 counters
even if only one is enabled.
This typically happens when using the "perf record" command in a guest
VM: perf will disable all event counters with PMCNTENTSET_EL0 and only
uses the cycle counter. And when using the "perf record" -F option with
a high profiling frequency, the overhead of KVM disabling all counters
instead of one on every counter interrupt becomes very noticeable.
The problem is fixed by having KVM disable only counters which are
enabled in PMCNTENSET_EL0. If a counter is not enabled in PMCNTENSET_EL0
then KVM will not enable it when setting PMCR_EL0.E and it will remain
disabled as long as it is not enabled in PMCNTENSET_EL0. So there is
effectively no need to disable a counter when clearing PMCR_EL0.E if it
is not enabled PMCNTENSET_EL0.
Acked-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Alexandru Elisei <alexandru.elisei@arm.com>
Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
[maz: moved 'mask' close to the actual user, simplifying the patch]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210712170345.660272-1-alexandre.chartre@oracle.com
---
arch/arm64/kvm/pmu-emul.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/kvm/pmu-emul.c b/arch/arm64/kvm/pmu-emul.c
index fae4e95b586c..dc65b58dc68f 100644
--- a/arch/arm64/kvm/pmu-emul.c
+++ b/arch/arm64/kvm/pmu-emul.c
@@ -563,20 +563,21 @@ void kvm_pmu_software_increment(struct kvm_vcpu *vcpu, u64 val)
*/
void kvm_pmu_handle_pmcr(struct kvm_vcpu *vcpu, u64 val)
{
- unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
int i;
if (val & ARMV8_PMU_PMCR_E) {
kvm_pmu_enable_counter_mask(vcpu,
__vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
} else {
- kvm_pmu_disable_counter_mask(vcpu, mask);
+ kvm_pmu_disable_counter_mask(vcpu,
+ __vcpu_sys_reg(vcpu, PMCNTENSET_EL0));
}
if (val & ARMV8_PMU_PMCR_C)
kvm_pmu_set_counter_value(vcpu, ARMV8_PMU_CYCLE_IDX, 0);
if (val & ARMV8_PMU_PMCR_P) {
+ unsigned long mask = kvm_pmu_valid_counter_mask(vcpu);
mask &= ~BIT(ARMV8_PMU_CYCLE_IDX);
for_each_set_bit(i, &mask, 32)
kvm_pmu_set_counter_value(vcpu, i, 0);
--
2.30.2
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^ permalink raw reply related [flat|nested] 13+ messages in thread* [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
2021-07-19 12:38 [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
` (2 preceding siblings ...)
2021-07-19 12:39 ` [PATCH v2 3/4] KVM: arm64: Disabling disabled PMU counters wastes a lot of time Marc Zyngier
@ 2021-07-19 12:39 ` Marc Zyngier
2021-07-19 16:35 ` Alexandru Elisei
2021-08-02 13:39 ` [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
4 siblings, 1 reply; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 12:39 UTC (permalink / raw)
To: linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandru Elisei,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team
We keep an entry for the PMSWINC_EL0 register in the vcpu structure,
while *never* writing anything there outside of reset.
Given that the register is defined as write-only, that we always
trap when this register is accessed, there is little point in saving
anything anyway.
Get rid of the entry, and save a mighty 8 bytes per vcpu structure.
We still need to keep it exposed to userspace in order to preserve
backward compatibility with previously saved VMs. Since userspace
cannot expect any effect of writing to PMSWINC_EL0, treat the
register as RAZ/WI for the purpose of userspace access.
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
arch/arm64/include/asm/kvm_host.h | 1 -
arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
2 files changed, 20 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 41911585ae0c..afc169630884 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -185,7 +185,6 @@ enum vcpu_sysreg {
PMCNTENSET_EL0, /* Count Enable Set Register */
PMINTENSET_EL1, /* Interrupt Enable Set Register */
PMOVSSET_EL0, /* Overflow Flag Status Set Register */
- PMSWINC_EL0, /* Software Increment Register */
PMUSERENR_EL0, /* User Enable Register */
/* Pointer Authentication Registers in a strict increasing order. */
diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index f22139658e48..a1f5101f49a3 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1286,6 +1286,20 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
return __set_id_reg(vcpu, rd, uaddr, true);
}
+static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
+ const struct kvm_one_reg *reg, void __user *uaddr)
+{
+ int err;
+ u64 val;
+
+ /* Perform the access even if we are going to ignore the value */
+ err = reg_from_user(&val, uaddr, sys_reg_to_index(rd));
+ if (err)
+ return err;
+
+ return 0;
+}
+
static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
const struct sys_reg_desc *r)
{
@@ -1629,8 +1643,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
.access = access_pmcnten, .reg = PMCNTENSET_EL0 },
{ PMU_SYS_REG(SYS_PMOVSCLR_EL0),
.access = access_pmovs, .reg = PMOVSSET_EL0 },
+ /*
+ * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
+ * previously (and pointlessly) advertised in the past...
+ */
{ PMU_SYS_REG(SYS_PMSWINC_EL0),
- .access = access_pmswinc, .reg = PMSWINC_EL0 },
+ .get_user = get_raz_id_reg, .set_user = set_wi_reg,
+ .access = access_pmswinc, .reset = NULL },
{ PMU_SYS_REG(SYS_PMSELR_EL0),
.access = access_pmselr, .reset = reset_pmselr, .reg = PMSELR_EL0 },
{ PMU_SYS_REG(SYS_PMCEID0_EL0),
--
2.30.2
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^ permalink raw reply related [flat|nested] 13+ messages in thread* Re: [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
2021-07-19 12:39 ` [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register Marc Zyngier
@ 2021-07-19 16:35 ` Alexandru Elisei
2021-07-19 16:56 ` Marc Zyngier
0 siblings, 1 reply; 13+ messages in thread
From: Alexandru Elisei @ 2021-07-19 16:35 UTC (permalink / raw)
To: Marc Zyngier, linux-arm-kernel, kvm, kvmarm
Cc: James Morse, Suzuki K Poulose, Alexandre Chartre, Robin Murphy,
Andrew Jones, Russell King, kernel-team
Hi Marc,
On 7/19/21 1:39 PM, Marc Zyngier wrote:
> We keep an entry for the PMSWINC_EL0 register in the vcpu structure,
> while *never* writing anything there outside of reset.
>
> Given that the register is defined as write-only, that we always
> trap when this register is accessed, there is little point in saving
> anything anyway.
>
> Get rid of the entry, and save a mighty 8 bytes per vcpu structure.
>
> We still need to keep it exposed to userspace in order to preserve
> backward compatibility with previously saved VMs. Since userspace
> cannot expect any effect of writing to PMSWINC_EL0, treat the
> register as RAZ/WI for the purpose of userspace access.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/kvm_host.h | 1 -
> arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
> 2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 41911585ae0c..afc169630884 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -185,7 +185,6 @@ enum vcpu_sysreg {
> PMCNTENSET_EL0, /* Count Enable Set Register */
> PMINTENSET_EL1, /* Interrupt Enable Set Register */
> PMOVSSET_EL0, /* Overflow Flag Status Set Register */
> - PMSWINC_EL0, /* Software Increment Register */
> PMUSERENR_EL0, /* User Enable Register */
>
> /* Pointer Authentication Registers in a strict increasing order. */
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index f22139658e48..a1f5101f49a3 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1286,6 +1286,20 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> return __set_id_reg(vcpu, rd, uaddr, true);
> }
>
> +static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> + const struct kvm_one_reg *reg, void __user *uaddr)
> +{
> + int err;
> + u64 val;
> +
> + /* Perform the access even if we are going to ignore the value */
> + err = reg_from_user(&val, uaddr, sys_reg_to_index(rd));
I don't understand why the read still happens if the value is ignored. Just so KVM
preserves the previous behaviour and tells userspace there was an error?
> + if (err)
> + return err;
> +
> + return 0;
> +}
> +
> static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> const struct sys_reg_desc *r)
> {
> @@ -1629,8 +1643,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
> { PMU_SYS_REG(SYS_PMOVSCLR_EL0),
> .access = access_pmovs, .reg = PMOVSSET_EL0 },
> + /*
> + * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
> + * previously (and pointlessly) advertised in the past...
> + */
> { PMU_SYS_REG(SYS_PMSWINC_EL0),
> - .access = access_pmswinc, .reg = PMSWINC_EL0 },
> + .get_user = get_raz_id_reg, .set_user = set_wi_reg,
In my opinion, the call chain to return 0 looks pretty confusing to me, as the
functions seemed made for ID register accesses, and the leaf function,
read_id_reg(), tries to match this register with a list of ID registers. Since we
have already added a new function just for PMSWINC_EL0, I was wondering if adding
another function, something like get_raz_reg(), would make more sense.
Thanks,
Alex
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^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
2021-07-19 16:35 ` Alexandru Elisei
@ 2021-07-19 16:56 ` Marc Zyngier
2021-07-20 16:44 ` Alexandru Elisei
0 siblings, 1 reply; 13+ messages in thread
From: Marc Zyngier @ 2021-07-19 16:56 UTC (permalink / raw)
To: Alexandru Elisei
Cc: linux-arm-kernel, kvm, kvmarm, James Morse, Suzuki K Poulose,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team
Hi Alex,
On 2021-07-19 17:35, Alexandru Elisei wrote:
> Hi Marc,
>
> On 7/19/21 1:39 PM, Marc Zyngier wrote:
>> We keep an entry for the PMSWINC_EL0 register in the vcpu structure,
>> while *never* writing anything there outside of reset.
>>
>> Given that the register is defined as write-only, that we always
>> trap when this register is accessed, there is little point in saving
>> anything anyway.
>>
>> Get rid of the entry, and save a mighty 8 bytes per vcpu structure.
>>
>> We still need to keep it exposed to userspace in order to preserve
>> backward compatibility with previously saved VMs. Since userspace
>> cannot expect any effect of writing to PMSWINC_EL0, treat the
>> register as RAZ/WI for the purpose of userspace access.
>>
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> ---
>> arch/arm64/include/asm/kvm_host.h | 1 -
>> arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
>> 2 files changed, 20 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h
>> b/arch/arm64/include/asm/kvm_host.h
>> index 41911585ae0c..afc169630884 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -185,7 +185,6 @@ enum vcpu_sysreg {
>> PMCNTENSET_EL0, /* Count Enable Set Register */
>> PMINTENSET_EL1, /* Interrupt Enable Set Register */
>> PMOVSSET_EL0, /* Overflow Flag Status Set Register */
>> - PMSWINC_EL0, /* Software Increment Register */
>> PMUSERENR_EL0, /* User Enable Register */
>>
>> /* Pointer Authentication Registers in a strict increasing order. */
>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>> index f22139658e48..a1f5101f49a3 100644
>> --- a/arch/arm64/kvm/sys_regs.c
>> +++ b/arch/arm64/kvm/sys_regs.c
>> @@ -1286,6 +1286,20 @@ static int set_raz_id_reg(struct kvm_vcpu
>> *vcpu, const struct sys_reg_desc *rd,
>> return __set_id_reg(vcpu, rd, uaddr, true);
>> }
>>
>> +static int set_wi_reg(struct kvm_vcpu *vcpu, const struct
>> sys_reg_desc *rd,
>> + const struct kvm_one_reg *reg, void __user *uaddr)
>> +{
>> + int err;
>> + u64 val;
>> +
>> + /* Perform the access even if we are going to ignore the value */
>> + err = reg_from_user(&val, uaddr, sys_reg_to_index(rd));
>
> I don't understand why the read still happens if the value is ignored.
> Just so KVM
> preserves the previous behaviour and tells userspace there was an
> error?
If userspace has given us a duff pointer, it needs to know about it.
>> + if (err)
>> + return err;
>> +
>> + return 0;
>> +}
>> +
>> static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params
>> *p,
>> const struct sys_reg_desc *r)
>> {
>> @@ -1629,8 +1643,13 @@ static const struct sys_reg_desc
>> sys_reg_descs[] = {
>> .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
>> { PMU_SYS_REG(SYS_PMOVSCLR_EL0),
>> .access = access_pmovs, .reg = PMOVSSET_EL0 },
>> + /*
>> + * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
>> + * previously (and pointlessly) advertised in the past...
>> + */
>> { PMU_SYS_REG(SYS_PMSWINC_EL0),
>> - .access = access_pmswinc, .reg = PMSWINC_EL0 },
>> + .get_user = get_raz_id_reg, .set_user = set_wi_reg,
>
> In my opinion, the call chain to return 0 looks pretty confusing to me,
> as the
> functions seemed made for ID register accesses, and the leaf function,
> read_id_reg(), tries to match this register with a list of ID
> registers. Since we
> have already added a new function just for PMSWINC_EL0, I was
> wondering if adding
> another function, something like get_raz_reg(), would make more sense.
In that case, I'd rather just kill get_raz_id_reg() and replace it with
this get_raz_reg(). If we trat something as RAZ, who cares whether it is
an idreg or not?
M.
--
Jazz is not dead. It just smells funny...
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^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
2021-07-19 16:56 ` Marc Zyngier
@ 2021-07-20 16:44 ` Alexandru Elisei
2021-07-21 9:30 ` Marc Zyngier
0 siblings, 1 reply; 13+ messages in thread
From: Alexandru Elisei @ 2021-07-20 16:44 UTC (permalink / raw)
To: Marc Zyngier
Cc: linux-arm-kernel, kvm, kvmarm, James Morse, Suzuki K Poulose,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team
Hi Marc,
On 7/19/21 5:56 PM, Marc Zyngier wrote:
> Hi Alex,
>
> On 2021-07-19 17:35, Alexandru Elisei wrote:
>> Hi Marc,
>>
>> On 7/19/21 1:39 PM, Marc Zyngier wrote:
>>> We keep an entry for the PMSWINC_EL0 register in the vcpu structure,
>>> while *never* writing anything there outside of reset.
>>>
>>> Given that the register is defined as write-only, that we always
>>> trap when this register is accessed, there is little point in saving
>>> anything anyway.
>>>
>>> Get rid of the entry, and save a mighty 8 bytes per vcpu structure.
>>>
>>> We still need to keep it exposed to userspace in order to preserve
>>> backward compatibility with previously saved VMs. Since userspace
>>> cannot expect any effect of writing to PMSWINC_EL0, treat the
>>> register as RAZ/WI for the purpose of userspace access.
>>>
>>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>>> ---
>>> arch/arm64/include/asm/kvm_host.h | 1 -
>>> arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
>>> 2 files changed, 20 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/kvm_host.h
>>> b/arch/arm64/include/asm/kvm_host.h
>>> index 41911585ae0c..afc169630884 100644
>>> --- a/arch/arm64/include/asm/kvm_host.h
>>> +++ b/arch/arm64/include/asm/kvm_host.h
>>> @@ -185,7 +185,6 @@ enum vcpu_sysreg {
>>> PMCNTENSET_EL0, /* Count Enable Set Register */
>>> PMINTENSET_EL1, /* Interrupt Enable Set Register */
>>> PMOVSSET_EL0, /* Overflow Flag Status Set Register */
>>> - PMSWINC_EL0, /* Software Increment Register */
>>> PMUSERENR_EL0, /* User Enable Register */
>>>
>>> /* Pointer Authentication Registers in a strict increasing order. */
>>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
>>> index f22139658e48..a1f5101f49a3 100644
>>> --- a/arch/arm64/kvm/sys_regs.c
>>> +++ b/arch/arm64/kvm/sys_regs.c
>>> @@ -1286,6 +1286,20 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const
>>> struct sys_reg_desc *rd,
>>> return __set_id_reg(vcpu, rd, uaddr, true);
>>> }
>>>
>>> +static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
>>> + const struct kvm_one_reg *reg, void __user *uaddr)
>>> +{
>>> + int err;
>>> + u64 val;
>>> +
>>> + /* Perform the access even if we are going to ignore the value */
>>> + err = reg_from_user(&val, uaddr, sys_reg_to_index(rd));
>>
>> I don't understand why the read still happens if the value is ignored.
>> Just so KVM
>> preserves the previous behaviour and tells userspace there was an error?
>
> If userspace has given us a duff pointer, it needs to know about it.
Makes sense, thanks.
>
>>> + if (err)
>>> + return err;
>>> +
>>> + return 0;
>>> +}
>>> +
>>> static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
>>> const struct sys_reg_desc *r)
>>> {
>>> @@ -1629,8 +1643,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>>> .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
>>> { PMU_SYS_REG(SYS_PMOVSCLR_EL0),
>>> .access = access_pmovs, .reg = PMOVSSET_EL0 },
>>> + /*
>>> + * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
>>> + * previously (and pointlessly) advertised in the past...
>>> + */
>>> { PMU_SYS_REG(SYS_PMSWINC_EL0),
>>> - .access = access_pmswinc, .reg = PMSWINC_EL0 },
>>> + .get_user = get_raz_id_reg, .set_user = set_wi_reg,
>>
>> In my opinion, the call chain to return 0 looks pretty confusing to me, as the
>> functions seemed made for ID register accesses, and the leaf function,
>> read_id_reg(), tries to match this register with a list of ID
>> registers. Since we
>> have already added a new function just for PMSWINC_EL0, I was
>> wondering if adding
>> another function, something like get_raz_reg(), would make more sense.
>
> In that case, I'd rather just kill get_raz_id_reg() and replace it with
> this get_raz_reg(). If we trat something as RAZ, who cares whether it is
> an idreg or not?
I agree, the Arm ARM doesn't make the distinction between ID registers and other
system registers in the definition of RAZ, I don't think KVM should either. And
the way read_id_reg() is written allows returning a value different than 0 even if
raz is true, which in my opinion could only happen because of a bug in KVM.
I can have a go at writing the patch(es) on top of this series, if you want. At
the moment I'm rewriting the KVM SPE series, so it will be a few weeks until I get
around to doing it though.
Thanks,
Alex
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^ permalink raw reply [flat|nested] 13+ messages in thread* Re: [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
2021-07-20 16:44 ` Alexandru Elisei
@ 2021-07-21 9:30 ` Marc Zyngier
0 siblings, 0 replies; 13+ messages in thread
From: Marc Zyngier @ 2021-07-21 9:30 UTC (permalink / raw)
To: Alexandru Elisei
Cc: linux-arm-kernel, kvm, kvmarm, James Morse, Suzuki K Poulose,
Alexandre Chartre, Robin Murphy, Andrew Jones, Russell King,
kernel-team
On Tue, 20 Jul 2021 17:44:32 +0100,
Alexandru Elisei <alexandru.elisei@arm.com> wrote:
>
> Hi Marc,
>
> On 7/19/21 5:56 PM, Marc Zyngier wrote:
> > Hi Alex,
> >
> > On 2021-07-19 17:35, Alexandru Elisei wrote:
> >> Hi Marc,
> >>
> >> On 7/19/21 1:39 PM, Marc Zyngier wrote:
> >>> We keep an entry for the PMSWINC_EL0 register in the vcpu structure,
> >>> while *never* writing anything there outside of reset.
> >>>
> >>> Given that the register is defined as write-only, that we always
> >>> trap when this register is accessed, there is little point in saving
> >>> anything anyway.
> >>>
> >>> Get rid of the entry, and save a mighty 8 bytes per vcpu structure.
> >>>
> >>> We still need to keep it exposed to userspace in order to preserve
> >>> backward compatibility with previously saved VMs. Since userspace
> >>> cannot expect any effect of writing to PMSWINC_EL0, treat the
> >>> register as RAZ/WI for the purpose of userspace access.
> >>>
> >>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> >>> ---
> >>> arch/arm64/include/asm/kvm_host.h | 1 -
> >>> arch/arm64/kvm/sys_regs.c | 21 ++++++++++++++++++++-
> >>> 2 files changed, 20 insertions(+), 2 deletions(-)
> >>>
> >>> diff --git a/arch/arm64/include/asm/kvm_host.h
> >>> b/arch/arm64/include/asm/kvm_host.h
> >>> index 41911585ae0c..afc169630884 100644
> >>> --- a/arch/arm64/include/asm/kvm_host.h
> >>> +++ b/arch/arm64/include/asm/kvm_host.h
> >>> @@ -185,7 +185,6 @@ enum vcpu_sysreg {
> >>> PMCNTENSET_EL0, /* Count Enable Set Register */
> >>> PMINTENSET_EL1, /* Interrupt Enable Set Register */
> >>> PMOVSSET_EL0, /* Overflow Flag Status Set Register */
> >>> - PMSWINC_EL0, /* Software Increment Register */
> >>> PMUSERENR_EL0, /* User Enable Register */
> >>>
> >>> /* Pointer Authentication Registers in a strict increasing order. */
> >>> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> >>> index f22139658e48..a1f5101f49a3 100644
> >>> --- a/arch/arm64/kvm/sys_regs.c
> >>> +++ b/arch/arm64/kvm/sys_regs.c
> >>> @@ -1286,6 +1286,20 @@ static int set_raz_id_reg(struct kvm_vcpu *vcpu, const
> >>> struct sys_reg_desc *rd,
> >>> return __set_id_reg(vcpu, rd, uaddr, true);
> >>> }
> >>>
> >>> +static int set_wi_reg(struct kvm_vcpu *vcpu, const struct sys_reg_desc *rd,
> >>> + const struct kvm_one_reg *reg, void __user *uaddr)
> >>> +{
> >>> + int err;
> >>> + u64 val;
> >>> +
> >>> + /* Perform the access even if we are going to ignore the value */
> >>> + err = reg_from_user(&val, uaddr, sys_reg_to_index(rd));
> >>
> >> I don't understand why the read still happens if the value is ignored.
> >> Just so KVM
> >> preserves the previous behaviour and tells userspace there was an error?
> >
> > If userspace has given us a duff pointer, it needs to know about it.
>
> Makes sense, thanks.
>
> >
> >>> + if (err)
> >>> + return err;
> >>> +
> >>> + return 0;
> >>> +}
> >>> +
> >>> static bool access_ctr(struct kvm_vcpu *vcpu, struct sys_reg_params *p,
> >>> const struct sys_reg_desc *r)
> >>> {
> >>> @@ -1629,8 +1643,13 @@ static const struct sys_reg_desc sys_reg_descs[] = {
> >>> .access = access_pmcnten, .reg = PMCNTENSET_EL0 },
> >>> { PMU_SYS_REG(SYS_PMOVSCLR_EL0),
> >>> .access = access_pmovs, .reg = PMOVSSET_EL0 },
> >>> + /*
> >>> + * PM_SWINC_EL0 is exposed to userspace as RAZ/WI, as it was
> >>> + * previously (and pointlessly) advertised in the past...
> >>> + */
> >>> { PMU_SYS_REG(SYS_PMSWINC_EL0),
> >>> - .access = access_pmswinc, .reg = PMSWINC_EL0 },
> >>> + .get_user = get_raz_id_reg, .set_user = set_wi_reg,
> >>
> >> In my opinion, the call chain to return 0 looks pretty confusing to me, as the
> >> functions seemed made for ID register accesses, and the leaf function,
> >> read_id_reg(), tries to match this register with a list of ID
> >> registers. Since we
> >> have already added a new function just for PMSWINC_EL0, I was
> >> wondering if adding
> >> another function, something like get_raz_reg(), would make more sense.
> >
> > In that case, I'd rather just kill get_raz_id_reg() and replace it with
> > this get_raz_reg(). If we trat something as RAZ, who cares whether it is
> > an idreg or not?
>
> I agree, the Arm ARM doesn't make the distinction between ID
> registers and other system registers in the definition of RAZ, I
> don't think KVM should either. And the way read_id_reg() is written
> allows returning a value different than 0 even if raz is true, which
> in my opinion could only happen because of a bug in KVM.
>
> I can have a go at writing the patch(es) on top of this series, if
> you want. At the moment I'm rewriting the KVM SPE series, so it will
> be a few weeks until I get around to doing it though.
We can do that at any time, it is just a cleanup without any guest or
userspace visible effect. If a get a spare hour, I'll have a
look. Otherwise, this can wait a bit.
Thanks,
M.
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^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more)
2021-07-19 12:38 [PATCH v2 0/4] kvm-arm64: Fix PMU reset values (and more) Marc Zyngier
` (3 preceding siblings ...)
2021-07-19 12:39 ` [PATCH v2 4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register Marc Zyngier
@ 2021-08-02 13:39 ` Marc Zyngier
4 siblings, 0 replies; 13+ messages in thread
From: Marc Zyngier @ 2021-08-02 13:39 UTC (permalink / raw)
To: linux-arm-kernel, Marc Zyngier, kvmarm, kvm
Cc: Andrew Jones, Robin Murphy, Alexandru Elisei, Alexandre Chartre,
Russell King, kernel-team, Suzuki K Poulose, James Morse
On Mon, 19 Jul 2021 13:38:58 +0100, Marc Zyngier wrote:
> This is the second version of the series initially posted at [1].
>
> * From v1:
> - Simplified masking in patch #1
> - Added a patch dropping PMSWINC_EL0 as a shadow register, though it
> is still advertised to userspace for the purpose of backward
> compatibility of VM save/restore
> - Collected ABs/RBs, with thanks
>
> [...]
Applied to next, thanks!
[1/4] KVM: arm64: Narrow PMU sysreg reset values to architectural requirements
commit: 0ab410a93d627ae73136d1a52c096262360b7992
[2/4] KVM: arm64: Drop unnecessary masking of PMU registers
commit: f5eff40058a856c23c5ec2f31756f107a2b1ef84
[3/4] KVM: arm64: Disabling disabled PMU counters wastes a lot of time
commit: ca4f202d08ba7f24cc97dce14c6d20ec7a679135
[4/4] KVM: arm64: Remove PMSWINC_EL0 shadow register
commit: 7a3ba3095a32f9c4ec8f30d680fea5150e12c3f3
Cheers,
M.
--
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^ permalink raw reply [flat|nested] 13+ messages in thread