linux-kernel - Re: [PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect in Host EL0

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Message-ID: <b85dcdc2-d56d-4bf7-9fa9-222a6f057674@arm.com>
Date: Tue, 29 Oct 2024 15:15:59 +0530
From: Anshuman Khandual <anshuman.khandual@....com>
To: Oliver Upton <oliver.upton@...ux.dev>, Marc Zyngier <maz@...nel.org>
Cc: kvmarm@...ts.linux.dev, Joey Gouly <joey.gouly@....com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Zenghui Yu
 <yuzenghui@...wei.com>, Catalin Marinas <catalin.marinas@....com>,
 Will Deacon <will@...nel.org>, linux-arm-kernel@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect
 in Host EL0



On 10/26/24 20:05, Oliver Upton wrote:
> Hey,
> 
> On Sat, Oct 26, 2024 at 09:13:17AM +0100, Marc Zyngier wrote:
>> On Fri, 25 Oct 2024 19:23:43 +0100,
>> Oliver Upton <oliver.upton@...ux.dev> wrote:
>>>
>>> Wire up the other end of traps that affect host EL0 by actually
>>> injecting them into the guest hypervisor. Skip over FGT entirely, as a
>>> cursory glance suggests no FGT is effective in host EL0.
>>
>> Yes, and this (thankfully) is by design! :-)
>>
>>>
>>> Note that kvm_inject_nested() is already equipped for handling
>>> exceptions while the VM is already in a host context.
>>>
>>> Signed-off-by: Oliver Upton <oliver.upton@...ux.dev>
>>> ---
>>>  arch/arm64/include/asm/kvm_emulate.h |  5 +++++
>>>  arch/arm64/kvm/emulate-nested.c      | 29 ++++++++++++++++++++++++----
>>>  2 files changed, 30 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
>>> index a601a9305b10..bf0c48403f59 100644
>>> --- a/arch/arm64/include/asm/kvm_emulate.h
>>> +++ b/arch/arm64/include/asm/kvm_emulate.h
>>> @@ -225,6 +225,11 @@ static inline bool is_hyp_ctxt(const struct kvm_vcpu *vcpu)
>>>  	return vcpu_has_nv(vcpu) && __is_hyp_ctxt(&vcpu->arch.ctxt);
>>>  }
>>>  
>>> +static inline bool vcpu_is_host_el0(const struct kvm_vcpu *vcpu)
>>> +{
>>> +	return is_hyp_ctxt(vcpu) && !vcpu_is_el2(vcpu);
>>> +}
>>> +
>>>  /*
>>>   * The layout of SPSR for an AArch32 state is different when observed from an
>>>   * AArch64 SPSR_ELx or an AArch32 SPSR_*. This function generates the AArch32
>>> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
>>> index e1a30d1bcd06..db3149379a4d 100644
>>> --- a/arch/arm64/kvm/emulate-nested.c
>>> +++ b/arch/arm64/kvm/emulate-nested.c
>>> @@ -20,6 +20,9 @@ enum trap_behaviour {
>>>  	BEHAVE_FORWARD_READ	= BIT(0),
>>>  	BEHAVE_FORWARD_WRITE	= BIT(1),
>>>  	BEHAVE_FORWARD_RW	= BEHAVE_FORWARD_READ | BEHAVE_FORWARD_WRITE,
>>> +
>>> +	/* Traps that take effect in Host EL0, this is rare! */
>>> +	BEHAVE_IN_HOST_EL0	= BIT(2),
>>
>> nit: BEHAVE_IN_HOST_EL0 lacks an action verb (forward?).
> 
> Thinking I'll squash this in (plus renaming in later patches):

Right, the following additional replacements are required for build.


@@ -307,14 +307,14 @@ static const struct trap_bits coarse_trap_bits[] = {
                .value          = MDCR_EL2_TPMCR,
                .mask           = MDCR_EL2_TPMCR,
                .behaviour      = BEHAVE_FORWARD_RW |
-                                 BEHAVE_IN_HOST_EL0,
+                                 BEHAVE_FORWARD_IN_HOST_EL0,
        },
        [CGT_MDCR_TPM] = {
                .index          = MDCR_EL2,
                .value          = MDCR_EL2_TPM,
                .mask           = MDCR_EL2_TPM,
                .behaviour      = BEHAVE_FORWARD_RW |
-                                 BEHAVE_IN_HOST_EL0,
+                                 BEHAVE_FORWARD_IN_HOST_EL0,
        },
        [CGT_MDCR_TDE] = {
                .index          = MDCR_EL2,
@@ -530,7 +530,7 @@ static enum trap_behaviour check_mdcr_hpmn(struct kvm_vcpu *vcpu)
        }
 
        if (kvm_pmu_counter_is_hyp(vcpu, idx))
-               return BEHAVE_FORWARD_RW | BEHAVE_IN_HOST_EL0;
+               return BEHAVE_FORWARD_RW | BEHAVE_FORWARD_IN_HOST_EL0;
 
        return BEHAVE_HANDLE_LOCALLY;
 }

> 
> diff --git a/arch/arm64/kvm/emulate-nested.c b/arch/arm64/kvm/emulate-nested.c
> index db3149379a4d..b072098ee44e 100644
> --- a/arch/arm64/kvm/emulate-nested.c
> +++ b/arch/arm64/kvm/emulate-nested.c
> @@ -22,7 +22,7 @@ enum trap_behaviour {
>  	BEHAVE_FORWARD_RW	= BEHAVE_FORWARD_READ | BEHAVE_FORWARD_WRITE,
>  
>  	/* Traps that take effect in Host EL0, this is rare! */
> -	BEHAVE_IN_HOST_EL0	= BIT(2),
> +	BEHAVE_FORWARD_IN_HOST_EL0	= BIT(2),
>  };
>  
>  struct trap_bits {
> @@ -2279,7 +2279,7 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
>  
>  	b = compute_trap_behaviour(vcpu, tc);
>  
> -	if (!(b & BEHAVE_IN_HOST_EL0) && vcpu_is_host_el0(vcpu))
> +	if (!(b & BEHAVE_FORWARD_IN_HOST_EL0) && vcpu_is_host_el0(vcpu))
>  		goto local;
>  
>  	if (((b & BEHAVE_FORWARD_READ) && is_read) ||
>