linux-kernel - Re: [PATCH v4 2/2] arm64: kvm: Introduce MTE VCPU feature

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Date:   Tue, 17 Nov 2020 16:07:48 +0000
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 v4 2/2] arm64: kvm: Introduce MTE VCPU feature

Hi Steven,

On Mon, Oct 26, 2020 at 03:57:27PM +0000, Steven Price wrote:
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 19aacc7d64de..38fe25310ca1 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -862,6 +862,26 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	if (vma_pagesize == PAGE_SIZE && !force_pte)
>  		vma_pagesize = transparent_hugepage_adjust(memslot, hva,
>  							   &pfn, &fault_ipa);
> +
> +	/*
> +	 * The otherwise redundant test for system_supports_mte() allows the
> +	 * code to be compiled out when CONFIG_ARM64_MTE is not present.
> +	 */
> +	if (system_supports_mte() && kvm->arch.mte_enabled && pfn_valid(pfn)) {
> +		/*
> +		 * VM will be able to see the page's tags, so we must ensure
> +		 * they have been initialised.
> +		 */
> +		struct page *page = pfn_to_page(pfn);
> +		long i, nr_pages = compound_nr(page);
> +
> +		/* if PG_mte_tagged is set, tags have already been initialised */
> +		for (i = 0; i < nr_pages; i++, page++) {
> +			if (!test_and_set_bit(PG_mte_tagged, &page->flags))
> +				mte_clear_page_tags(page_address(page));
> +		}
> +	}

If this page was swapped out and mapped back in, where does the
restoring from swap happen?

I may have asked in the past, is user_mem_abort() the only path for
mapping Normal pages into stage 2?

-- 
Catalin