Re: [PATCH 15/18] KVM: arm64: Warn when PENDING_EXCEPTION and INCREMENT_PC are set together

From: Fuad Tabba <tabba@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	James Morse <james.morse@arm.com>,
	 Suzuki K Poulose <suzuki.poulose@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	 Oliver Upton <oupton@google.com>, Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	 Mark Brown <broonie@kernel.org>,
	kernel-team@android.com
Subject: Re: [PATCH 15/18] KVM: arm64: Warn when PENDING_EXCEPTION and INCREMENT_PC are set together
Date: Wed, 8 Jun 2022 16:16:55 +0100	[thread overview]
Message-ID: <CA+EHjTyW62HaJdH_L1RMBzQpzkNbFBAYpXQ-y_Wg4u1a2eVJwA@mail.gmail.com> (raw)
In-Reply-To: <20220528113829.1043361-16-maz@kernel.org>

Hi Marc,

On Sat, May 28, 2022 at 12:49 PM Marc Zyngier <maz@kernel.org> wrote:
>
> We really don't want PENDING_EXCEPTION and INCREMENT_PC to ever be
> set at the same time, as they are mutually exclusive. Add checks
> that will generate a warning should this ever happen.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/kvm_emulate.h | 1 +
>  arch/arm64/kvm/hyp/nvhe/sys_regs.c   | 2 ++
>  arch/arm64/kvm/inject_fault.c        | 8 ++++++++
>  3 files changed, 11 insertions(+)
>
> diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h
> index 46e631cd8d9e..861fa0b24a7f 100644
> --- a/arch/arm64/include/asm/kvm_emulate.h
> +++ b/arch/arm64/include/asm/kvm_emulate.h
> @@ -473,6 +473,7 @@ static inline unsigned long vcpu_data_host_to_guest(struct kvm_vcpu *vcpu,
>
>  static __always_inline void kvm_incr_pc(struct kvm_vcpu *vcpu)
>  {
> +       WARN_ON(vcpu_get_flag(vcpu, PENDING_EXCEPTION));
>         vcpu_set_flag(vcpu, INCREMENT_PC);
>  }
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/sys_regs.c b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> index 2841a2d447a1..04973984b6db 100644
> --- a/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> +++ b/arch/arm64/kvm/hyp/nvhe/sys_regs.c
> @@ -38,6 +38,8 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
>         *vcpu_pc(vcpu) = read_sysreg_el2(SYS_ELR);
>         *vcpu_cpsr(vcpu) = read_sysreg_el2(SYS_SPSR);
>
> +       WARN_ON(vcpu_get_flag(vcpu, INCREMENT_PC));
> +
>         vcpu_set_flag(vcpu, PENDING_EXCEPTION);
>         vcpu_set_flag(vcpu, EXCEPT_AA64_EL1_SYNC);
>
> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> index a9a7b513f3b0..2f4b9afc16ec 100644
> --- a/arch/arm64/kvm/inject_fault.c
> +++ b/arch/arm64/kvm/inject_fault.c
> @@ -20,6 +20,8 @@ static void inject_abt64(struct kvm_vcpu *vcpu, bool is_iabt, unsigned long addr
>         bool is_aarch32 = vcpu_mode_is_32bit(vcpu);
>         u32 esr = 0;
>
> +       WARN_ON(vcpu_get_flag(vcpu, INCREMENT_PC));
> +

Minor nit: While we're at it, should we just create a helper for
setting PENDING_EXCEPTION, same as we have for INCREMENT_PC? That
might make the code clearer and save us from the hassle of having this
WARN_ON before every instance of setting PENDING_EXCEPTION?

Cheers,
/fuad

>         vcpu_set_flag(vcpu, PENDING_EXCEPTION);
>         vcpu_set_flag(vcpu, EXCEPT_AA64_EL1_SYNC);
>
> @@ -51,6 +53,8 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
>  {
>         u32 esr = (ESR_ELx_EC_UNKNOWN << ESR_ELx_EC_SHIFT);
>
> +       WARN_ON(vcpu_get_flag(vcpu, INCREMENT_PC));
> +
>         vcpu_set_flag(vcpu, PENDING_EXCEPTION);
>         vcpu_set_flag(vcpu, EXCEPT_AA64_EL1_SYNC);
>
> @@ -71,6 +75,8 @@ static void inject_undef64(struct kvm_vcpu *vcpu)
>
>  static void inject_undef32(struct kvm_vcpu *vcpu)
>  {
> +       WARN_ON(vcpu_get_flag(vcpu, INCREMENT_PC));
> +
>         vcpu_set_flag(vcpu, PENDING_EXCEPTION);
>         vcpu_set_flag(vcpu, EXCEPT_AA32_UND);
>  }
> @@ -94,6 +100,8 @@ static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt, u32 addr)
>
>         far = vcpu_read_sys_reg(vcpu, FAR_EL1);
>
> +       WARN_ON(vcpu_get_flag(vcpu, INCREMENT_PC));
> +
>         if (is_pabt) {
>                 vcpu_set_flag(vcpu, PENDING_EXCEPTION);
>                 vcpu_set_flag(vcpu, EXCEPT_AA32_IABT);
> --
> 2.34.1
>

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