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From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Ard Biesheuvel <ardb@kernel.org>, Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	Sean Christopherson <seanjc@google.com>,
	David Matlack <dmatlack@google.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: arm64: Disable interrupts while walking userspace PTs
Date: Fri, 17 Mar 2023 09:03:50 +0000	[thread overview]
Message-ID: <760caa64691576b728c224bbbfdd18a4@kernel.org> (raw)
In-Reply-To: <ZBOpVLEPEJazjyGD@linux.dev>

On 2023-03-16 23:42, Oliver Upton wrote:
> Marc,
> 
> On Thu, Mar 16, 2023 at 05:45:45PM +0000, Marc Zyngier wrote:
>> We walk the userspace PTs to discover what mapping size was
>> used there. However, this can race against the userspace tables
>> being freed, and we end-up in the weeds.
>> 
>> Thankfully, the mm code is being generous and will IPI us when
>> doing so. So let's implement our part of the bargain and disable
>> interrupts around the walk. This ensures that nothing terrible
>> happens during that time.
>> 
>> We still need to handle the removal of the page tables before
>> the walk. For that, allow get_user_mapping_size() to return an
>> error, and make sure this error can be propagated all the way
>> to the the exit handler.
>> 
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> Cc: stable@vger.kernel.org
> 
> Looks good. I've squashed in this meaningless diff to make use of an 
> existing
> helper.
> 
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index e95593736ae3..3b9d4d24c361 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -691,7 +691,7 @@ static int get_user_mapping_size(struct kvm *kvm, 
> u64 addr)
>  		return -EFAULT;
> 
>  	/* Oops, the userspace PTs are gone... Replay the fault */
> -	if (!(pte & PTE_VALID))
> +	if (!kvm_pte_valid(pte))
>  		return -EAGAIN;

Sure, LGTM.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Oliver Upton <oliver.upton@linux.dev>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	kvm@vger.kernel.org, James Morse <james.morse@arm.com>,
	Suzuki K Poulose <suzuki.poulose@arm.com>,
	Zenghui Yu <yuzenghui@huawei.com>,
	Ard Biesheuvel <ardb@kernel.org>, Will Deacon <will@kernel.org>,
	Quentin Perret <qperret@google.com>,
	Sean Christopherson <seanjc@google.com>,
	David Matlack <dmatlack@google.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v2 1/2] KVM: arm64: Disable interrupts while walking userspace PTs
Date: Fri, 17 Mar 2023 09:03:50 +0000	[thread overview]
Message-ID: <760caa64691576b728c224bbbfdd18a4@kernel.org> (raw)
In-Reply-To: <ZBOpVLEPEJazjyGD@linux.dev>

On 2023-03-16 23:42, Oliver Upton wrote:
> Marc,
> 
> On Thu, Mar 16, 2023 at 05:45:45PM +0000, Marc Zyngier wrote:
>> We walk the userspace PTs to discover what mapping size was
>> used there. However, this can race against the userspace tables
>> being freed, and we end-up in the weeds.
>> 
>> Thankfully, the mm code is being generous and will IPI us when
>> doing so. So let's implement our part of the bargain and disable
>> interrupts around the walk. This ensures that nothing terrible
>> happens during that time.
>> 
>> We still need to handle the removal of the page tables before
>> the walk. For that, allow get_user_mapping_size() to return an
>> error, and make sure this error can be propagated all the way
>> to the the exit handler.
>> 
>> Signed-off-by: Marc Zyngier <maz@kernel.org>
>> Cc: stable@vger.kernel.org
> 
> Looks good. I've squashed in this meaningless diff to make use of an 
> existing
> helper.
> 
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index e95593736ae3..3b9d4d24c361 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -691,7 +691,7 @@ static int get_user_mapping_size(struct kvm *kvm, 
> u64 addr)
>  		return -EFAULT;
> 
>  	/* Oops, the userspace PTs are gone... Replay the fault */
> -	if (!(pte & PTE_VALID))
> +	if (!kvm_pte_valid(pte))
>  		return -EAGAIN;

Sure, LGTM.

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...

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http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2023-03-17  9:03 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-03-16 17:45 [PATCH v2 0/2] KVM: arm64: Plug a couple of MM races Marc Zyngier
2023-03-16 17:45 ` Marc Zyngier
2023-03-16 17:45 ` [PATCH v2 1/2] KVM: arm64: Disable interrupts while walking userspace PTs Marc Zyngier
2023-03-16 17:45   ` Marc Zyngier
2023-03-16 23:42   ` Oliver Upton
2023-03-16 23:42     ` Oliver Upton
2023-03-17  9:03     ` Marc Zyngier [this message]
2023-03-17  9:03       ` Marc Zyngier
2023-03-16 17:45 ` [PATCH v2 2/2] KVM: arm64: Check for kvm_vma_mte_allowed in the critical section Marc Zyngier
2023-03-16 17:45   ` Marc Zyngier
2023-03-17  1:20 ` [PATCH v2 0/2] KVM: arm64: Plug a couple of MM races Oliver Upton
2023-03-17  1:20   ` Oliver Upton

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