linux-kernel - Re: [PATCH v1 2/2] kvm: arm64: handle single-step of userspace mmio instructions

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Date:   Fri, 6 Oct 2017 14:13:38 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     Alex Bennée <alex.bennee@...aro.org>,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, christoffer.dall@...aro.org,
        marc.zyngier@....com
Cc:     Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/2] kvm: arm64: handle single-step of userspace mmio
 instructions



On 06/10/17 12:39, Alex Bennée wrote:
> The system state of KVM when using userspace emulation is not complete
> until we return into KVM_RUN. To handle mmio related updates we wait
> until they have been committed and then schedule our KVM_EXIT_DEBUG.
> 
> I've introduced a new function kvm_arm_maybe_return_debug() to wrap up
> the differences between arm/arm64 which is currently null for arm.
> 
> Signed-off-by: Alex Bennée <alex.bennee@...aro.org>
> ---
>   arch/arm/include/asm/kvm_host.h   |  2 ++
>   arch/arm64/include/asm/kvm_host.h |  1 +
>   arch/arm64/kvm/debug.c            | 21 +++++++++++++++++++++
>   arch/arm64/kvm/handle_exit.c      |  9 +++------
>   virt/kvm/arm/arm.c                |  2 +-
>   virt/kvm/arm/mmio.c               |  3 ++-
>   6 files changed, 30 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
> index 4a879f6ff13b..aec943f6d123 100644
> --- a/arch/arm/include/asm/kvm_host.h
> +++ b/arch/arm/include/asm/kvm_host.h
> @@ -285,6 +285,8 @@ static inline void kvm_arm_init_debug(void) {}
>   static inline void kvm_arm_setup_debug(struct kvm_vcpu *vcpu) {}
>   static inline void kvm_arm_clear_debug(struct kvm_vcpu *vcpu) {}
>   static inline void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu) {}
> +static inline int  kvm_arm_maybe_return_debug(struct kvm_vcpu *vcpu,
> +						struct kvm_run *run) {}
>   

This function should return 1.

>   int kvm_arm_vcpu_arch_set_attr(struct kvm_vcpu *vcpu,
>   			       struct kvm_device_attr *attr);
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index e923b58606e2..fa67d21662f6 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -369,6 +369,7 @@ void kvm_arm_init_debug(void);
>   void kvm_arm_setup_debug(struct kvm_vcpu *vcpu);
>   void kvm_arm_clear_debug(struct kvm_vcpu *vcpu);
>   void kvm_arm_reset_debug_ptr(struct kvm_vcpu *vcpu);
> +int  kvm_arm_maybe_return_debug(struct kvm_vcpu *vcpu, struct kvm_run *run);

I feel the name could be a little bit more explicit:

kvm_arm_trap_need_step_debug, kvm_arm_trap_step_return_debug, 
kvm_arm_trap_need_return_debug.

At least, I think it would be nice that the name reflect that this check 
is meant for emulated instructions.

Otherwise:

Reviewed-by: Julien Thierry <julien.thierry@....com>

Thanks,

-- 
Julien Thierry