* [PATCH] arm: KVM: force execution of HCPTR access on VM exit
@ 2015-03-16 10:59 Marc Zyngier
2015-04-08 11:40 ` Christoffer Dall
0 siblings, 1 reply; 4+ messages in thread
From: Marc Zyngier @ 2015-03-16 10:59 UTC (permalink / raw)
To: linux-arm-kernel
On VM entry, we disable access to the VFP registers in order to
perform a lazy save/restore of these registers.
On VM exit, we restore access, test if we did enable them before,
and save/restore the guest/host registers if necessary. In this
sequence, the FPEXC register is always accessed, irrespective
of the trapping configuration.
If the guest didn't touch the VFP registers, then the HCPTR access
has now enabled such access, but we're missing a barrier to ensure
architectural execution of the new HCPTR configuration. If the HCPTR
access has been delayed/reordered, the subsequent access to FPEXC
will cause a trap, which we aren't prepared to handle at all.
The fix is to introduce a barrier that only takes place if the
guest hasn't accessed its view of the VFP registers, making
the access to FPEXC safe.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm/kvm/interrupts.S | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
index 79caf79..3ac7aca 100644
--- a/arch/arm/kvm/interrupts.S
+++ b/arch/arm/kvm/interrupts.S
@@ -175,10 +175,13 @@ __kvm_vcpu_return:
#ifdef CONFIG_VFPv3
@ Save floating point registers we if let guest use them.
tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
- bne after_vfp_restore
+ beq 1f
+
+ isb @ Force execution of HCPTR if we've just reenabled VFP access
+ b after_vfp_restore
@ Switch VFP/NEON hardware state to the host's
- add r7, vcpu, #VCPU_VFP_GUEST
+1: add r7, vcpu, #VCPU_VFP_GUEST
store_vfp_state r7
add r7, vcpu, #VCPU_VFP_HOST
ldr r7, [r7]
--
2.1.4
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [PATCH] arm: KVM: force execution of HCPTR access on VM exit
2015-03-16 10:59 [PATCH] arm: KVM: force execution of HCPTR access on VM exit Marc Zyngier
@ 2015-04-08 11:40 ` Christoffer Dall
2015-04-08 17:16 ` Marc Zyngier
0 siblings, 1 reply; 4+ messages in thread
From: Christoffer Dall @ 2015-04-08 11:40 UTC (permalink / raw)
To: linux-arm-kernel
On Mon, Mar 16, 2015 at 10:59:43AM +0000, Marc Zyngier wrote:
> On VM entry, we disable access to the VFP registers in order to
> perform a lazy save/restore of these registers.
>
> On VM exit, we restore access, test if we did enable them before,
> and save/restore the guest/host registers if necessary. In this
> sequence, the FPEXC register is always accessed, irrespective
> of the trapping configuration.
>
> If the guest didn't touch the VFP registers, then the HCPTR access
> has now enabled such access, but we're missing a barrier to ensure
> architectural execution of the new HCPTR configuration. If the HCPTR
> access has been delayed/reordered, the subsequent access to FPEXC
> will cause a trap, which we aren't prepared to handle at all.
>
> The fix is to introduce a barrier that only takes place if the
> guest hasn't accessed its view of the VFP registers, making
> the access to FPEXC safe.
>
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
> arch/arm/kvm/interrupts.S | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
> index 79caf79..3ac7aca 100644
> --- a/arch/arm/kvm/interrupts.S
> +++ b/arch/arm/kvm/interrupts.S
> @@ -175,10 +175,13 @@ __kvm_vcpu_return:
> #ifdef CONFIG_VFPv3
> @ Save floating point registers we if let guest use them.
> tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
> - bne after_vfp_restore
> + beq 1f
> +
> + isb @ Force execution of HCPTR if we've just reenabled VFP access
> + b after_vfp_restore
>
> @ Switch VFP/NEON hardware state to the host's
> - add r7, vcpu, #VCPU_VFP_GUEST
> +1: add r7, vcpu, #VCPU_VFP_GUEST
> store_vfp_state r7
> add r7, vcpu, #VCPU_VFP_HOST
> ldr r7, [r7]
> --
> 2.1.4
>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] arm: KVM: force execution of HCPTR access on VM exit
2015-04-08 11:40 ` Christoffer Dall
@ 2015-04-08 17:16 ` Marc Zyngier
2015-04-09 13:35 ` Christoffer Dall
0 siblings, 1 reply; 4+ messages in thread
From: Marc Zyngier @ 2015-04-08 17:16 UTC (permalink / raw)
To: linux-arm-kernel
On 08/04/15 12:40, Christoffer Dall wrote:
> On Mon, Mar 16, 2015 at 10:59:43AM +0000, Marc Zyngier wrote:
>> On VM entry, we disable access to the VFP registers in order to
>> perform a lazy save/restore of these registers.
>>
>> On VM exit, we restore access, test if we did enable them before,
>> and save/restore the guest/host registers if necessary. In this
>> sequence, the FPEXC register is always accessed, irrespective
>> of the trapping configuration.
>>
>> If the guest didn't touch the VFP registers, then the HCPTR access
>> has now enabled such access, but we're missing a barrier to ensure
>> architectural execution of the new HCPTR configuration. If the HCPTR
>> access has been delayed/reordered, the subsequent access to FPEXC
>> will cause a trap, which we aren't prepared to handle at all.
>>
>> The fix is to introduce a barrier that only takes place if the
>> guest hasn't accessed its view of the VFP registers, making
>> the access to FPEXC safe.
>>
>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>> ---
>> arch/arm/kvm/interrupts.S | 7 +++++--
>> 1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
>> index 79caf79..3ac7aca 100644
>> --- a/arch/arm/kvm/interrupts.S
>> +++ b/arch/arm/kvm/interrupts.S
>> @@ -175,10 +175,13 @@ __kvm_vcpu_return:
>> #ifdef CONFIG_VFPv3
>> @ Save floating point registers we if let guest use them.
>> tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
>> - bne after_vfp_restore
>> + beq 1f
>> +
>> + isb @ Force execution of HCPTR if we've just reenabled VFP access
>> + b after_vfp_restore
>>
>> @ Switch VFP/NEON hardware state to the host's
>> - add r7, vcpu, #VCPU_VFP_GUEST
>> +1: add r7, vcpu, #VCPU_VFP_GUEST
>> store_vfp_state r7
>> add r7, vcpu, #VCPU_VFP_HOST
>> ldr r7, [r7]
>> --
>> 2.1.4
>>
>
> Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Thanks (I must admit I completely forgot the existence of this patch...).
I guess we can queue that for -rc1, with a Cc to stable...
M.
--
Jazz is not dead. It just smells funny...
^ permalink raw reply [flat|nested] 4+ messages in thread
* [PATCH] arm: KVM: force execution of HCPTR access on VM exit
2015-04-08 17:16 ` Marc Zyngier
@ 2015-04-09 13:35 ` Christoffer Dall
0 siblings, 0 replies; 4+ messages in thread
From: Christoffer Dall @ 2015-04-09 13:35 UTC (permalink / raw)
To: linux-arm-kernel
On Wed, Apr 08, 2015 at 06:16:50PM +0100, Marc Zyngier wrote:
> On 08/04/15 12:40, Christoffer Dall wrote:
> > On Mon, Mar 16, 2015 at 10:59:43AM +0000, Marc Zyngier wrote:
> >> On VM entry, we disable access to the VFP registers in order to
> >> perform a lazy save/restore of these registers.
> >>
> >> On VM exit, we restore access, test if we did enable them before,
> >> and save/restore the guest/host registers if necessary. In this
> >> sequence, the FPEXC register is always accessed, irrespective
> >> of the trapping configuration.
> >>
> >> If the guest didn't touch the VFP registers, then the HCPTR access
> >> has now enabled such access, but we're missing a barrier to ensure
> >> architectural execution of the new HCPTR configuration. If the HCPTR
> >> access has been delayed/reordered, the subsequent access to FPEXC
> >> will cause a trap, which we aren't prepared to handle at all.
> >>
> >> The fix is to introduce a barrier that only takes place if the
> >> guest hasn't accessed its view of the VFP registers, making
> >> the access to FPEXC safe.
> >>
> >> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> >> ---
> >> arch/arm/kvm/interrupts.S | 7 +++++--
> >> 1 file changed, 5 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/arm/kvm/interrupts.S b/arch/arm/kvm/interrupts.S
> >> index 79caf79..3ac7aca 100644
> >> --- a/arch/arm/kvm/interrupts.S
> >> +++ b/arch/arm/kvm/interrupts.S
> >> @@ -175,10 +175,13 @@ __kvm_vcpu_return:
> >> #ifdef CONFIG_VFPv3
> >> @ Save floating point registers we if let guest use them.
> >> tst r2, #(HCPTR_TCP(10) | HCPTR_TCP(11))
> >> - bne after_vfp_restore
> >> + beq 1f
> >> +
> >> + isb @ Force execution of HCPTR if we've just reenabled VFP access
> >> + b after_vfp_restore
> >>
> >> @ Switch VFP/NEON hardware state to the host's
> >> - add r7, vcpu, #VCPU_VFP_GUEST
> >> +1: add r7, vcpu, #VCPU_VFP_GUEST
> >> store_vfp_state r7
> >> add r7, vcpu, #VCPU_VFP_HOST
> >> ldr r7, [r7]
> >> --
> >> 2.1.4
> >>
> >
> > Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
>
> Thanks (I must admit I completely forgot the existence of this patch...).
>
> I guess we can queue that for -rc1, with a Cc to stable...
>
yes, I tested it on TC2 (both A15 and A7) and it works like a charm.
-Christoffer
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2015-04-08 11:40 ` Christoffer Dall
2015-04-08 17:16 ` Marc Zyngier
2015-04-09 13:35 ` Christoffer Dall
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