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

Oliver Upton posted 18 patches 1 month ago
[PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect in Host EL0
Posted by Oliver Upton 1 month ago 
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.

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@linux.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),
 };
 
 struct trap_bits {
@@ -2128,11 +2131,19 @@ static u64 kvm_get_sysreg_res0(struct kvm *kvm, enum vcpu_sysreg sr)
 	return masks->mask[sr - __VNCR_START__].res0;
 }
 
-static bool check_fgt_bit(struct kvm *kvm, bool is_read,
+static bool check_fgt_bit(struct kvm_vcpu *vcpu, bool is_read,
 			  u64 val, const union trap_config tc)
 {
+	struct kvm *kvm = vcpu->kvm;
 	enum vcpu_sysreg sr;
 
+	/*
+	 * KVM doesn't know about any FGTs that apply to the host, and hopefully
+	 * that'll remain the case.
+	 */
+	if (is_hyp_ctxt(vcpu))
+		return false;
+
 	if (tc.pol)
 		return (val & BIT(tc.bit));
 
@@ -2209,7 +2220,15 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
 	 * If we're not nesting, immediately return to the caller, with the
 	 * sysreg index, should we have it.
 	 */
-	if (!vcpu_has_nv(vcpu) || is_hyp_ctxt(vcpu))
+	if (!vcpu_has_nv(vcpu))
+		goto local;
+
+	/*
+	 * There are a few traps that take effect InHost, but are constrained
+	 * to EL0. Don't bother with computing the trap behaviour if the vCPU
+	 * isn't in EL0.
+	 */
+	if (is_hyp_ctxt(vcpu) && !vcpu_is_host_el0(vcpu))
 		goto local;
 
 	switch ((enum fgt_group_id)tc.fgt) {
@@ -2255,12 +2274,14 @@ bool triage_sysreg_trap(struct kvm_vcpu *vcpu, int *sr_index)
 		goto local;
 	}
 
-	if (tc.fgt != __NO_FGT_GROUP__ && check_fgt_bit(vcpu->kvm, is_read,
-							val, tc))
+	if (tc.fgt != __NO_FGT_GROUP__ && check_fgt_bit(vcpu, is_read, val, tc))
 		goto inject;
 
 	b = compute_trap_behaviour(vcpu, tc);
 
+	if (!(b & BEHAVE_IN_HOST_EL0) && vcpu_is_host_el0(vcpu))
+		goto local;
+
 	if (((b & BEHAVE_FORWARD_READ) && is_read) ||
 	    ((b & BEHAVE_FORWARD_WRITE) && !is_read))
 		goto inject;
-- 
2.47.0.163.g1226f6d8fa-goog
Re: [PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect in Host EL0
Posted by Marc Zyngier 1 month ago 
On Fri, 25 Oct 2024 19:23:43 +0100,
Oliver Upton <oliver.upton@linux.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@linux.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?).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.
Re: [PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect in Host EL0
Posted by Oliver Upton 4 weeks, 1 day ago 
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@linux.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@linux.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):

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) ||

-- 
Thanks,
Oliver
Re: [PATCH v4 08/18] KVM: arm64: nv: Reinject traps that take effect in Host EL0
Posted by Anshuman Khandual 3 weeks, 6 days ago 

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@linux.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@linux.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) ||
>

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