Re: [PATCH RFCv2 6/9] kvm/arm64: Export kvm_handle_user_mem_abort() with prefault mode

From: Gavin Shan <gshan@redhat.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: aarcange@redhat.com, drjones@redhat.com, suzuki.poulose@arm.com,
	catalin.marinas@arm.com, linux-kernel@vger.kernel.org,
	eric.auger@redhat.com, james.morse@arm.com, shan.gavin@gmail.com,
	maz@kernel.org, will@kernel.org, kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFCv2 6/9] kvm/arm64: Export kvm_handle_user_mem_abort() with prefault mode
Date: Wed, 27 May 2020 13:01:29 +1000	[thread overview]
Message-ID: <8d758b47-3fb0-ee70-700f-fa8af407c115@redhat.com> (raw)
In-Reply-To: <20200526105807.GE1363@C02TD0UTHF1T.local>

Hi Mark,

On 5/26/20 8:58 PM, Mark Rutland wrote:
> On Fri, May 08, 2020 at 01:29:16PM +1000, Gavin Shan wrote:
>> This renames user_mem_abort() to kvm_handle_user_mem_abort(), and
>> then export it. The function will be used in asynchronous page fault
>> to populate a page table entry once the corresponding page is populated
>> from the backup device (e.g. swap partition):
>>
>>     * Parameter @fault_status is replace by @esr.
>>     * The parameters are reorder based on their importance.
> 
> It seems like multiple changes are going on here, and it would be
> clearer with separate patches.
> 
> Passing the ESR rather than the extracted fault status seems fine, but
> for clarirty it's be nicer to do this in its own patch.
> 

Ok. I'll have a separate patch to do this.

> Why is it necessary to re-order the function parameters? Does that align
> with other function prototypes?
> 

There are no explicit reasons for it. I can restore the order to what we
had previously if you like.

> What exactly is the `prefault` parameter meant to do? It doesn't do
> anything currently, so it'd be better to introduce it later when logic
> using it is instroduced, or where callers will pass distinct values.
> 

Yes, fair enough. I will merge the logic with PATCH[7] then.

> Thanks,
> Mark.
> 

Thanks,
Gavin

>>
>> This shouldn't cause any functional changes.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   arch/arm64/include/asm/kvm_host.h |  4 ++++
>>   virt/kvm/arm/mmu.c                | 14 ++++++++------
>>   2 files changed, 12 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 32c8a675e5a4..f77c706777ec 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -437,6 +437,10 @@ int __kvm_arm_vcpu_set_events(struct kvm_vcpu *vcpu,
>>   			      struct kvm_vcpu_events *events);
>>   
>>   #define KVM_ARCH_WANT_MMU_NOTIFIER
>> +int kvm_handle_user_mem_abort(struct kvm_vcpu *vcpu, unsigned int esr,
>> +			      struct kvm_memory_slot *memslot,
>> +			      phys_addr_t fault_ipa, unsigned long hva,
>> +			      bool prefault);
>>   int kvm_unmap_hva_range(struct kvm *kvm,
>>   			unsigned long start, unsigned long end);
>>   int kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>> index e462e0368fd9..95aaabb2b1fc 100644
>> --- a/virt/kvm/arm/mmu.c
>> +++ b/virt/kvm/arm/mmu.c
>> @@ -1656,12 +1656,12 @@ static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
>>   	       (hva & ~(map_size - 1)) + map_size <= uaddr_end;
>>   }
>>   
>> -static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> -			  struct kvm_memory_slot *memslot, unsigned long hva,
>> -			  unsigned long fault_status)
>> +int kvm_handle_user_mem_abort(struct kvm_vcpu *vcpu, unsigned int esr,
>> +			      struct kvm_memory_slot *memslot,
>> +			      phys_addr_t fault_ipa, unsigned long hva,
>> +			      bool prefault)
>>   {
>> -	int ret;
>> -	u32 esr = kvm_vcpu_get_esr(vcpu);
>> +	unsigned int fault_status = kvm_vcpu_trap_get_fault_type(esr);
>>   	bool write_fault, writable, force_pte = false;
>>   	bool exec_fault, needs_exec;
>>   	unsigned long mmu_seq;
>> @@ -1674,6 +1674,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   	pgprot_t mem_type = PAGE_S2;
>>   	bool logging_active = memslot_is_logging(memslot);
>>   	unsigned long vma_pagesize, flags = 0;
>> +	int ret;
>>   
>>   	write_fault = kvm_is_write_fault(esr);
>>   	exec_fault = kvm_vcpu_trap_is_iabt(esr);
>> @@ -1995,7 +1996,8 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
>>   		goto out_unlock;
>>   	}
>>   
>> -	ret = user_mem_abort(vcpu, fault_ipa, memslot, hva, fault_status);
>> +	ret = kvm_handle_user_mem_abort(vcpu, esr, memslot,
>> +					fault_ipa, hva, false);
>>   	if (ret == 0)
>>   		ret = 1;
>>   out:
>> -- 
>> 2.23.0
>>
> 

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