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

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Message-ID: <9d4ef6cf-2333-83b8-c555-e70b99b95b28@arm.com>
Date:   Wed, 17 Jun 2020 16:34:13 +0100
From:   Steven Price <steven.price@....com>
To:     Catalin Marinas <catalin.marinas@....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 Poulose <Suzuki.Poulose@....com>,
        "kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dave P Martin <Dave.Martin@....com>,
        Mark Rutland <Mark.Rutland@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH 2/2] arm64: kvm: Introduce MTE VCPU feature

On 17/06/2020 15:38, Catalin Marinas wrote:
> On Wed, Jun 17, 2020 at 01:38:44PM +0100, Steven Price wrote:
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index e3b9ee268823..040a7fffaa93 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -1783,6 +1783,17 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   			vma_pagesize = PMD_SIZE;
>>   	}
>>   
>> +	if (system_supports_mte() && kvm->arch.vcpu_has_mte) {
>> +		/*
>> +		 * 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);
>> +
>> +		if (!test_and_set_bit(PG_mte_tagged, &page->flags))
>> +			mte_clear_page_tags(page_address(page), page_size(page));
>> +	}
> 
> Are all the guest pages always mapped via a Stage 2 fault? It may be
> better if we did that via kvm_set_spte_hva().
> 

I was under the impression that pages are always faulted into the stage 
2, but I have to admit I'm not 100% sure about that.

kvm_set_spte_hva() may be more appropriate, although on first look I 
don't understand how that function deals with huge pages. Is it actually 
called for normal mappings or only for changes due to the likes of KSM?

Steve