linux-kernel - Re: [PATCH] ARM: KVM: Handle IPA unmapping on memory region deletion

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Date:	Thu, 03 Apr 2014 18:32:16 +0200
From:	Eric Auger <eric.auger@...aro.org>
To:	Marc Zyngier <marc.zyngier@....com>
CC:	"eric.auger@...com" <eric.auger@...com>,
	"christoffer.dall@...aro.org" <christoffer.dall@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"christophe.barnichon@...com" <christophe.barnichon@...com>
Subject: Re: [PATCH] ARM: KVM: Handle IPA unmapping on memory region deletion

On 04/03/2014 05:26 PM, Marc Zyngier wrote:
> Hi Eric,
> 
> On 03/04/14 16:17, Eric Auger wrote:
>> Currently when a KVM region is removed using
>> kvm_vm_ioctl_set_memory_region (with memory region size equal to 0), the
>> corresponding intermediate physical memory is not unmapped.
>>
>> This patch unmaps the region's IPA range in
>> kvm_arch_commit_memory_region using unmap_stage2_range.
>>
>> The patch was tested on QEMU VFIO based use case where RAM memory region
>> creation/deletion frequently happens for IRQ handling.
>>
>> Notes:
>> - the KVM_MR_MOVE case shall request some similar addition but I cannot test
>>   this currently
> 
> I think you should try to handle it anyway. I'm sure you could hack QEMU
> to do this test it, but even if you don't, better plug that hole right now.

Hi Marc,

OK I will proceed

> 
>> Signed-off-by: Eric Auger <eric.auger@...aro.org>
>> ---
>>  arch/arm/include/asm/kvm_mmu.h | 2 ++
>>  arch/arm/kvm/arm.c             | 8 ++++++++
>>  arch/arm/kvm/mmu.c             | 2 +-
>>  3 files changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index 2d122ad..a91c863 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -52,6 +52,8 @@ void kvm_free_stage2_pgd(struct kvm *kvm);
>>  int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa,
>>  			  phys_addr_t pa, unsigned long size);
>>  
>> +void unmap_stage2_range(struct kvm *kvm, phys_addr_t guest_ipa, u64 size);
>> +
>>  int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run);
>>  
>>  void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index bd18bb8..9a4bc10 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -241,6 +241,14 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>>  				   const struct kvm_memory_slot *old,
>>  				   enum kvm_mr_change change)
>>  {
>> +	if (change == KVM_MR_DELETE) {
>> +		gpa_t gpa = old->base_gfn << PAGE_SHIFT;
>> +		u64 size = old->npages << PAGE_SHIFT;
>> +
>> +		spin_lock(&kvm->mmu_lock);
>> +		unmap_stage2_range(kvm, gpa, size);
>> +		spin_unlock(&kvm->mmu_lock);
>> +	}
>>  }
> 
> Just move the whole function to mmu.c, as it makes more sense to have it
> there. And while you're at it, how about moving the other
> memslot/memory_region stubs?

OK I will move:
kvm_arch_free_memslot,
kvm_arch_create_memslot,
kvm_arch_prepare_memory_region,
kvm_arch_commit_memory_region,
kvm_arch_shadow_all and
kvm_arch_shadow_memslot then.

Best Regards

Eric

> 
>>  void kvm_arch_flush_shadow_all(struct kvm *kvm)
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 7789857..e8580e2 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -443,7 +443,7 @@ int kvm_alloc_stage2_pgd(struct kvm *kvm)
>>   * destroying the VM), otherwise another faulting VCPU may come in and mess
>>   * with things behind our backs.
>>   */
>> -static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
>> +void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
>>  {
>>  	unmap_range(kvm, kvm->arch.pgd, start, size);
>>  }
>>
> 
> Looks sensible otherwise.
> 
> Thanks!
> 
> 	M.
> 

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