linux-kernel - Re: [PATCH v11 5/6] KVM: arm64: ioctl to fetch/store tags in a guest

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Message-ID: <20210427175844.GB17872@arm.com>
Date:   Tue, 27 Apr 2021 18:58:44 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Steven Price <steven.price@....com>
Cc:     Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, Dave Martin <Dave.Martin@....com>,
        Mark Rutland <mark.rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>, qemu-devel@...gnu.org,
        Juan Quintela <quintela@...hat.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Richard Henderson <richard.henderson@...aro.org>,
        Peter Maydell <peter.maydell@...aro.org>,
        Haibo Xu <Haibo.Xu@....com>, Andrew Jones <drjones@...hat.com>
Subject: Re: [PATCH v11 5/6] KVM: arm64: ioctl to fetch/store tags in a guest

On Fri, Apr 16, 2021 at 04:43:08PM +0100, Steven Price wrote:
> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
> index 24223adae150..2b85a047c37d 100644
> --- a/arch/arm64/include/uapi/asm/kvm.h
> +++ b/arch/arm64/include/uapi/asm/kvm.h
> @@ -184,6 +184,20 @@ struct kvm_vcpu_events {
>  	__u32 reserved[12];
>  };
>  
> +struct kvm_arm_copy_mte_tags {
> +	__u64 guest_ipa;
> +	__u64 length;
> +	union {
> +		void __user *addr;
> +		__u64 padding;
> +	};
> +	__u64 flags;
> +	__u64 reserved[2];
> +};

I know Marc asked for some reserved space in here but I'm not sure it's
the right place. And what's with the union of a 64-bit pointer and
64-bit padding, it doesn't change any layout? Maybe add the two reserved
values to the union in case we want to store something else in the
future.

Or maybe I'm missing something, I haven't checked how other KVM ioctls
work.

-- 
Catalin