linux-kernel - Re: [PATCH v13 5/8] KVM: arm64: Save/restore MTE registers

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Date:   Thu, 3 Jun 2021 17:48:06 +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 v13 5/8] KVM: arm64: Save/restore MTE registers

On Mon, May 24, 2021 at 11:45:10AM +0100, Steven Price wrote:
> diff --git a/arch/arm64/include/asm/kvm_mte.h b/arch/arm64/include/asm/kvm_mte.h
> new file mode 100644
> index 000000000000..eae4bce9e269
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_mte.h
> @@ -0,0 +1,68 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2020 ARM Ltd.

You may want to update some of the years.

> + */
> +#ifndef __ASM_KVM_MTE_H
> +#define __ASM_KVM_MTE_H
> +
> +#ifdef __ASSEMBLY__
> +
> +#include <asm/sysreg.h>
> +
> +#ifdef CONFIG_ARM64_MTE
> +
> +.macro mte_switch_to_guest g_ctxt, h_ctxt, reg1
> +alternative_if_not ARM64_MTE
> +	b	.L__skip_switch\@
> +alternative_else_nop_endif
> +	mrs	\reg1, hcr_el2
> +	and	\reg1, \reg1, #(HCR_ATA)
> +	cbz	\reg1, .L__skip_switch\@

Nitpick: TBZ would be shorter, though you need the bit number.

The patch looks fine (as per my understanding of the KVM context
switching code):

Reviewed-by: Catalin Marinas <catalin.marinas@....com>