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

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Message-ID: <87r083th7m.wl-maz@kernel.org>
Date: Sat, 26 Oct 2024 09:13:17 +0100
From: Marc Zyngier <maz@...nel.org>
To: Oliver Upton <oliver.upton@...ux.dev>
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

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?).

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.