* [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
@ 2018-10-17 16:42 ` Mark Rutland
0 siblings, 0 replies; 6+ messages in thread
From: Mark Rutland @ 2018-10-17 16:42 UTC (permalink / raw)
To: linux-arm-kernel; +Cc: Marc Zyngier, Will Deacon, Robin Murphy, kvmarm
At boot time, KVM stashes the host MDCR_EL2 value, but only does this
when the kernel is not running in hyp mode (i.e. is non-VHE). In these
cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
lead to CONSTRAINED UNPREDICTABLE behaviour.
Since we use this value to derive the MDCR_EL2 value when switching
to/from a guest, after a guest have been run, the performance counters
do not behave as expected. This has been observed to result in accesses
via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
counters, resulting in events not being counted. In these cases, only
the fixed-purpose cycle counter appears to work as expected.
Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Christopher Dall <christoffer.dall@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: kvmarm@lists.cs.columbia.edu
---
virt/kvm/arm/arm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index c92053bc3f96..8fb31a7cc22c 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
__cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
__cpu_init_stage2();
-
- kvm_arm_init_debug();
}
static void cpu_hyp_reset(void)
@@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
cpu_init_hyp_mode(NULL);
}
+ kvm_arm_init_debug();
+
if (vgic_present)
kvm_vgic_init_cpu_hardware();
}
--
2.11.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
@ 2018-10-17 16:42 ` Mark Rutland
0 siblings, 0 replies; 6+ messages in thread
From: Mark Rutland @ 2018-10-17 16:42 UTC (permalink / raw)
To: linux-arm-kernel
At boot time, KVM stashes the host MDCR_EL2 value, but only does this
when the kernel is not running in hyp mode (i.e. is non-VHE). In these
cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
lead to CONSTRAINED UNPREDICTABLE behaviour.
Since we use this value to derive the MDCR_EL2 value when switching
to/from a guest, after a guest have been run, the performance counters
do not behave as expected. This has been observed to result in accesses
via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
counters, resulting in events not being counted. In these cases, only
the fixed-purpose cycle counter appears to work as expected.
Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Christopher Dall <christoffer.dall@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: kvmarm at lists.cs.columbia.edu
---
virt/kvm/arm/arm.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
index c92053bc3f96..8fb31a7cc22c 100644
--- a/virt/kvm/arm/arm.c
+++ b/virt/kvm/arm/arm.c
@@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
__cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
__cpu_init_stage2();
-
- kvm_arm_init_debug();
}
static void cpu_hyp_reset(void)
@@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
cpu_init_hyp_mode(NULL);
}
+ kvm_arm_init_debug();
+
if (vgic_present)
kvm_vgic_init_cpu_hardware();
}
--
2.11.0
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
2018-10-17 16:42 ` Mark Rutland
@ 2018-10-17 16:51 ` Marc Zyngier
-1 siblings, 0 replies; 6+ messages in thread
From: Marc Zyngier @ 2018-10-17 16:51 UTC (permalink / raw)
To: Mark Rutland, linux-arm-kernel; +Cc: Robin Murphy, Will Deacon, kvmarm
On 17/10/18 17:42, Mark Rutland wrote:
> At boot time, KVM stashes the host MDCR_EL2 value, but only does this
> when the kernel is not running in hyp mode (i.e. is non-VHE). In these
> cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
> lead to CONSTRAINED UNPREDICTABLE behaviour.
>
> Since we use this value to derive the MDCR_EL2 value when switching
> to/from a guest, after a guest have been run, the performance counters
> do not behave as expected. This has been observed to result in accesses
> via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
> counters, resulting in events not being counted. In these cases, only
> the fixed-purpose cycle counter appears to work as expected.
>
> Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
>
> Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Christopher Dall <christoffer.dall@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: kvmarm@lists.cs.columbia.edu
> ---
> virt/kvm/arm/arm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index c92053bc3f96..8fb31a7cc22c 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
>
> __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
> __cpu_init_stage2();
> -
> - kvm_arm_init_debug();
> }
>
> static void cpu_hyp_reset(void)
> @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
> cpu_init_hyp_mode(NULL);
> }
>
> + kvm_arm_init_debug();
> +
> if (vgic_present)
> kvm_vgic_init_cpu_hardware();
> }
>
Urghh. Lovely. Thanks for tracking that one down. I'll queue it
immediately, with a Cc to stable.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
@ 2018-10-17 16:51 ` Marc Zyngier
0 siblings, 0 replies; 6+ messages in thread
From: Marc Zyngier @ 2018-10-17 16:51 UTC (permalink / raw)
To: linux-arm-kernel
On 17/10/18 17:42, Mark Rutland wrote:
> At boot time, KVM stashes the host MDCR_EL2 value, but only does this
> when the kernel is not running in hyp mode (i.e. is non-VHE). In these
> cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
> lead to CONSTRAINED UNPREDICTABLE behaviour.
>
> Since we use this value to derive the MDCR_EL2 value when switching
> to/from a guest, after a guest have been run, the performance counters
> do not behave as expected. This has been observed to result in accesses
> via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
> counters, resulting in events not being counted. In these cases, only
> the fixed-purpose cycle counter appears to work as expected.
>
> Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
>
> Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Christopher Dall <christoffer.dall@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: kvmarm at lists.cs.columbia.edu
> ---
> virt/kvm/arm/arm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index c92053bc3f96..8fb31a7cc22c 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
>
> __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
> __cpu_init_stage2();
> -
> - kvm_arm_init_debug();
> }
>
> static void cpu_hyp_reset(void)
> @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
> cpu_init_hyp_mode(NULL);
> }
>
> + kvm_arm_init_debug();
> +
> if (vgic_present)
> kvm_vgic_init_cpu_hardware();
> }
>
Urghh. Lovely. Thanks for tracking that one down. I'll queue it
immediately, with a Cc to stable.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
2018-10-17 16:42 ` Mark Rutland
@ 2018-10-17 17:13 ` Robin Murphy
-1 siblings, 0 replies; 6+ messages in thread
From: Robin Murphy @ 2018-10-17 17:13 UTC (permalink / raw)
To: Mark Rutland, linux-arm-kernel; +Cc: Marc Zyngier, Will Deacon, kvmarm
On 17/10/18 17:42, Mark Rutland wrote:
> At boot time, KVM stashes the host MDCR_EL2 value, but only does this
> when the kernel is not running in hyp mode (i.e. is non-VHE). In these
> cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
> lead to CONSTRAINED UNPREDICTABLE behaviour.
>
> Since we use this value to derive the MDCR_EL2 value when switching
> to/from a guest, after a guest have been run, the performance counters
> do not behave as expected. This has been observed to result in accesses
> via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
> counters, resulting in events not being counted. In these cases, only
> the fixed-purpose cycle counter appears to work as expected.
>
> Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
FWIW,
Tested-by: Robin Murphy <robin.murphy@arm.com>
> Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Christopher Dall <christoffer.dall@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: kvmarm@lists.cs.columbia.edu
> ---
> virt/kvm/arm/arm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index c92053bc3f96..8fb31a7cc22c 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
>
> __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
> __cpu_init_stage2();
> -
> - kvm_arm_init_debug();
> }
>
> static void cpu_hyp_reset(void)
> @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
> cpu_init_hyp_mode(NULL);
> }
>
> + kvm_arm_init_debug();
> +
> if (vgic_present)
> kvm_vgic_init_cpu_hardware();
> }
>
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value
@ 2018-10-17 17:13 ` Robin Murphy
0 siblings, 0 replies; 6+ messages in thread
From: Robin Murphy @ 2018-10-17 17:13 UTC (permalink / raw)
To: linux-arm-kernel
On 17/10/18 17:42, Mark Rutland wrote:
> At boot time, KVM stashes the host MDCR_EL2 value, but only does this
> when the kernel is not running in hyp mode (i.e. is non-VHE). In these
> cases, the stashed value of MDCR_EL2.HPMN happens to be zero, which can
> lead to CONSTRAINED UNPREDICTABLE behaviour.
>
> Since we use this value to derive the MDCR_EL2 value when switching
> to/from a guest, after a guest have been run, the performance counters
> do not behave as expected. This has been observed to result in accesses
> via PMXEVTYPER_EL0 and PMXEVCNTR_EL0 not affecting the relevant
> counters, resulting in events not being counted. In these cases, only
> the fixed-purpose cycle counter appears to work as expected.
>
> Fix this by always stashing the host MDCR_EL2 value, regardless of VHE.
FWIW,
Tested-by: Robin Murphy <robin.murphy@arm.com>
> Fixes: 1e947bad0b63b351 ("arm64: KVM: Skip HYP setup when already running in HYP")
> Signed-off-by: Mark Rutland <mark.rutland@arm.com>
> Cc: Christopher Dall <christoffer.dall@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Marc Zyngier <marc.zyngier@arm.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: kvmarm at lists.cs.columbia.edu
> ---
> virt/kvm/arm/arm.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
> index c92053bc3f96..8fb31a7cc22c 100644
> --- a/virt/kvm/arm/arm.c
> +++ b/virt/kvm/arm/arm.c
> @@ -1295,8 +1295,6 @@ static void cpu_init_hyp_mode(void *dummy)
>
> __cpu_init_hyp_mode(pgd_ptr, hyp_stack_ptr, vector_ptr);
> __cpu_init_stage2();
> -
> - kvm_arm_init_debug();
> }
>
> static void cpu_hyp_reset(void)
> @@ -1320,6 +1318,8 @@ static void cpu_hyp_reinit(void)
> cpu_init_hyp_mode(NULL);
> }
>
> + kvm_arm_init_debug();
> +
> if (vgic_present)
> kvm_vgic_init_cpu_hardware();
> }
>
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2018-10-17 17:13 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2018-10-17 16:42 [PATCH] kvm: arm64: fix caching of host MDCR_EL2 value Mark Rutland
2018-10-17 16:42 ` Mark Rutland
2018-10-17 16:51 ` Marc Zyngier
2018-10-17 16:51 ` Marc Zyngier
2018-10-17 17:13 ` Robin Murphy
2018-10-17 17:13 ` Robin Murphy
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