linux-kernel - Re: [PATCH 4/4] arm64: mte: Use stage-2 NoTagAccess memory attribute if supported

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Message-ID: <Zx-jWyF7xvFS-Vs6@linux.dev>
Date: Mon, 28 Oct 2024 14:44:43 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: "Aneesh Kumar K.V (Arm)" <aneesh.kumar@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, Suzuki K Poulose <Suzuki.Poulose@....com>,
	Steven Price <steven.price@....com>, Will Deacon <will@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Marc Zyngier <maz@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Joey Gouly <joey.gouly@....com>, Zenghui Yu <yuzenghui@...wei.com>
Subject: Re: [PATCH 4/4] arm64: mte: Use stage-2 NoTagAccess memory attribute
 if supported

On Mon, Oct 28, 2024 at 03:10:14PM +0530, Aneesh Kumar K.V (Arm) wrote:
> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> index 637efc055145..a8268a164c4d 100644
> --- a/include/uapi/linux/kvm.h
> +++ b/include/uapi/linux/kvm.h
> @@ -178,6 +178,7 @@ struct kvm_xen_exit {
>  #define KVM_EXIT_NOTIFY           37
>  #define KVM_EXIT_LOONGARCH_IOCSR  38
>  #define KVM_EXIT_MEMORY_FAULT     39
> +#define KVM_EXIT_ARM_NOTAG_ACCESS 40
>  
>  /* For KVM_EXIT_INTERNAL_ERROR */
>  /* Emulate instruction failed. */
> @@ -446,6 +447,12 @@ struct kvm_run {
>  			__u64 gpa;
>  			__u64 size;
>  		} memory_fault;
> +		/* KVM_EXIT_ARM_NOTAG_ACCESS */
> +		struct {
> +			__u64 flags;
> +			__u64 gpa;
> +			__u64 size;
> +		} notag_access;

Can you please look into reusing the memory fault exit infrastructure?

The entire point of that is for KVM to tell the VMM it cannot make
forward progress because of ${SOMETHING} unexpected at the specified
GPA. You can add a new flag that describes tag access.

-- 
Thanks,
Oliver