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

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Message-ID: <Zxz-LocgUKuzE3t0@linux.dev>
Date: Sat, 26 Oct 2024 14:35:26 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: 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>,
	Anshuman Khandual <anshuman.khandual@....com>,
	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

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):

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