linux-kernel - Re: [PATCH v2 1/3] KVM: x86: move kvm_vcpu_gfn_to_memslot() out of try_async

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Message-ID: <87k0xdwplg.fsf@vitty.brq.redhat.com>
Date:   Tue, 01 Sep 2020 16:15:07 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Peter Xu <peterx@...hat.com>, Michael Tsirkin <mst@...hat.com>,
        Julia Suvorova <jsuvorov@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Jones <drjones@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] KVM: x86: move kvm_vcpu_gfn_to_memslot() out of try_async_pf()

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> On Fri, Aug 07, 2020 at 04:12:30PM +0200, Vitaly Kuznetsov wrote:
>> No functional change intended. Slot flags will need to be analyzed
>> prior to try_async_pf() when KVM_MEM_PCI_HOLE is implemented.
>

(Sorry it took me so long to reply. No, I wasn't hoping for Paolo's
magical "queued, thanks", I just tried to not read my email while on
vacation).

> Why?  Wouldn't it be just as easy, and arguably more appropriate, to add
> KVM_PFN_ERR_PCI_HOLE and update handle_abornmal_pfn() accordinaly?
>

Yes, we can do that, but what I don't quite like here is that
try_async_pf() does much more than 'trying async PF'. In particular, it
extracts 'pfn' and this is far from being obvious. Maybe we can rename
try_async_pf() somewhat smartly (e.g. 'try_handle_pf()')? Your
suggestion will make perfect sense to me then.

>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>>  arch/x86/kvm/mmu/mmu.c         | 14 ++++++++------
>>  arch/x86/kvm/mmu/paging_tmpl.h |  7 +++++--
>>  2 files changed, 13 insertions(+), 8 deletions(-)
>> 
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index 862bf418214e..fef6956393f7 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -4042,11 +4042,10 @@ static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
>>  				  kvm_vcpu_gfn_to_hva(vcpu, gfn), &arch);
>>  }
>>  
>> -static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
>> -			 gpa_t cr2_or_gpa, kvm_pfn_t *pfn, bool write,
>> -			 bool *writable)
>> +static bool try_async_pf(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
>> +			 bool prefault, gfn_t gfn, gpa_t cr2_or_gpa,
>> +			 kvm_pfn_t *pfn, bool write, bool *writable)
>>  {
>> -	struct kvm_memory_slot *slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
>>  	bool async;
>>  
>>  	/* Don't expose private memslots to L2. */
>> @@ -4082,7 +4081,7 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>>  	bool exec = error_code & PFERR_FETCH_MASK;
>>  	bool lpage_disallowed = exec && is_nx_huge_page_enabled();
>>  	bool map_writable;
>> -
>> +	struct kvm_memory_slot *slot;
>>  	gfn_t gfn = gpa >> PAGE_SHIFT;
>>  	unsigned long mmu_seq;
>>  	kvm_pfn_t pfn;
>> @@ -4104,7 +4103,10 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
>>  	mmu_seq = vcpu->kvm->mmu_notifier_seq;
>>  	smp_rmb();
>>  
>> -	if (try_async_pf(vcpu, prefault, gfn, gpa, &pfn, write, &map_writable))
>> +	slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
>> +
>> +	if (try_async_pf(vcpu, slot, prefault, gfn, gpa, &pfn, write,
>> +			 &map_writable))
>>  		return RET_PF_RETRY;
>>  
>>  	if (handle_abnormal_pfn(vcpu, is_tdp ? 0 : gpa, gfn, pfn, ACC_ALL, &r))
>> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
>> index 0172a949f6a7..5c6a895f67c3 100644
>> --- a/arch/x86/kvm/mmu/paging_tmpl.h
>> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
>> @@ -779,6 +779,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
>>  	int write_fault = error_code & PFERR_WRITE_MASK;
>>  	int user_fault = error_code & PFERR_USER_MASK;
>>  	struct guest_walker walker;
>> +	struct kvm_memory_slot *slot;
>>  	int r;
>>  	kvm_pfn_t pfn;
>>  	unsigned long mmu_seq;
>> @@ -833,8 +834,10 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gpa_t addr, u32 error_code,
>>  	mmu_seq = vcpu->kvm->mmu_notifier_seq;
>>  	smp_rmb();
>>  
>> -	if (try_async_pf(vcpu, prefault, walker.gfn, addr, &pfn, write_fault,
>> -			 &map_writable))
>> +	slot = kvm_vcpu_gfn_to_memslot(vcpu, walker.gfn);
>> +
>> +	if (try_async_pf(vcpu, slot, prefault, walker.gfn, addr, &pfn,
>> +			 write_fault, &map_writable))
>>  		return RET_PF_RETRY;
>>  
>>  	if (handle_abnormal_pfn(vcpu, addr, walker.gfn, pfn, walker.pte_access, &r))
>> -- 
>> 2.25.4
>> 
>

-- 
Vitaly