linux-kernel - Re: [PATCH 3/3] kvm: arm/arm64: Fix locking for kvm_free_stage2

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Message-ID: <314fbde3-17e6-414b-85e6-326de22bdc1c@arm.com>
Date:   Wed, 15 Mar 2017 09:39:26 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Christoffer Dall <cdall@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, andreyknvl@...gle.com,
        dvyukov@...gle.com, christoffer.dall@...aro.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, kcc@...gle.com,
        syzkaller@...glegroups.com, will.deacon@....com,
        catalin.marinas@....com, pbonzini@...hat.com, mark.rutland@....com,
        ard.biesheuvel@...aro.org, stable@...r.kernel.org
Subject: Re: [PATCH 3/3] kvm: arm/arm64: Fix locking for kvm_free_stage2_pgd

On 15/03/17 09:21, Christoffer Dall wrote:
> On Tue, Mar 14, 2017 at 02:52:34PM +0000, Suzuki K Poulose wrote:
>> In kvm_free_stage2_pgd() we don't hold the kvm->mmu_lock while calling
>> unmap_stage2_range() on the entire memory range for the guest. This could
>> cause problems with other callers (e.g, munmap on a memslot) trying to
>> unmap a range.
>>
>> Fixes: commit d5d8184d35c9 ("KVM: ARM: Memory virtualization setup")
>> Cc: stable@...r.kernel.org # v3.10+
>> Cc: Marc Zyngier <marc.zyngier@....com>
>> Cc: Christoffer Dall <christoffer.dall@...aro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>  arch/arm/kvm/mmu.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 13b9c1f..b361f71 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -831,7 +831,10 @@ void kvm_free_stage2_pgd(struct kvm *kvm)
>>  	if (kvm->arch.pgd == NULL)
>>  		return;
>>  
>> +	spin_lock(&kvm->mmu_lock);
>>  	unmap_stage2_range(kvm, 0, KVM_PHYS_SIZE);
>> +	spin_unlock(&kvm->mmu_lock);
>> +
> 
> This ends up holding the spin lock for potentially quite a while, where
> we can do things like __flush_dcache_area(), which I think can fault.

I believe we're always using the linear mapping (or kmap on 32bit) in
order not to fault.

Thanks,

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