[PATCH 0/4] KVM: arm64: Minor page fault handler improvement

[PATCH 0/4] KVM: arm64: Minor page fault handler improvement

[Gavin Shan]

The series includes several minior improvements to stage-2 page fault
handler: PATCH[1/2] are cleaning up the code. PATCH[3] fixes the address
range check on adding new memory slot. PATCH[4] don't retrieve the memory
slot again in the page fault handler to save a bit CPU cycles.

Gavin Shan (4):
  KVM: arm64: Hide kvm_mmu_wp_memory_region()
  KVM: arm64: Use find_vma_intersection()
  KVM: arm64: Fix address check for memory slot
  KVM: arm64: Don't retrieve memory slot again in page fault handler

 arch/arm64/include/asm/kvm_host.h |  1 -
 arch/arm64/kvm/mmu.c              | 19 +++++++++++--------
 2 files changed, 11 insertions(+), 9 deletions(-)

-- 
2.23.0

[PATCH 1/4] KVM: arm64: Hide kvm_mmu_wp_memory_region()

[Gavin Shan]

We needn't expose the function as it's only used by mmu.c.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/include/asm/kvm_host.h | 1 -
 arch/arm64/kvm/mmu.c              | 2 +-
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 3d10e6527f7d..688f2df1957b 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -632,7 +632,6 @@ void kvm_arm_resume_guest(struct kvm *kvm);
 	})
 
 void force_vm_exit(const cpumask_t *mask);
-void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
 
 int handle_exit(struct kvm_vcpu *vcpu, int exception_index);
 void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index);
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 77cb2d28f2a4..84e70f953de6 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -555,7 +555,7 @@ static void stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_
  * Acquires kvm_mmu_lock. Called with kvm->slots_lock mutex acquired,
  * serializing operations for VM memory regions.
  */
-void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
+static void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
 {
 	struct kvm_memslots *slots = kvm_memslots(kvm);
 	struct kvm_memory_slot *memslot = id_to_memslot(slots, slot);
-- 
2.23.0

Re: [PATCH 1/4] KVM: arm64: Hide kvm_mmu_wp_memory_region()

[Keqian Zhu]

Hi Gavin,

This function is only used by mmu.c in the first commit c64735554c0a, so please feel free
to add:

Reviewed-by: Keqian Zhu <zhukeqian1@huawei.com>


Thanks,
Keqian

On 2021/3/15 12:18, Gavin Shan wrote:
> We needn't expose the function as it's only used by mmu.c.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/include/asm/kvm_host.h | 1 -
>  arch/arm64/kvm/mmu.c              | 2 +-
>  2 files changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 3d10e6527f7d..688f2df1957b 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -632,7 +632,6 @@ void kvm_arm_resume_guest(struct kvm *kvm);
>  	})
>  
>  void force_vm_exit(const cpumask_t *mask);
> -void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>  
>  int handle_exit(struct kvm_vcpu *vcpu, int exception_index);
>  void handle_exit_early(struct kvm_vcpu *vcpu, int exception_index);
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 77cb2d28f2a4..84e70f953de6 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -555,7 +555,7 @@ static void stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_
>   * Acquires kvm_mmu_lock. Called with kvm->slots_lock mutex acquired,
>   * serializing operations for VM memory regions.
>   */
> -void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
> +static void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
>  {
>  	struct kvm_memslots *slots = kvm_memslots(kvm);
>  	struct kvm_memory_slot *memslot = id_to_memslot(slots, slot);
> 

[PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Gavin Shan]

find_vma_intersection() has been existing to search the intersected
vma. This uses the function where it's applicable, to simplify the
code.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/kvm/mmu.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 84e70f953de6..286b603ed0d3 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
 	 *     +--------------------------------------------+
 	 */
 	do {
-		struct vm_area_struct *vma = find_vma(current->mm, hva);
+		struct vm_area_struct *vma;
 		hva_t vm_start, vm_end;
 
-		if (!vma || vma->vm_start >= reg_end)
+		vma = find_vma_intersection(current->mm, hva, reg_end);
+		if (!vma)
 			break;
 
 		/*
@@ -1330,10 +1331,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 *     +--------------------------------------------+
 	 */
 	do {
-		struct vm_area_struct *vma = find_vma(current->mm, hva);
+		struct vm_area_struct *vma;
 		hva_t vm_start, vm_end;
 
-		if (!vma || vma->vm_start >= reg_end)
+		vma = find_vma_intersection(current->mm, hva, reg_end);
+		if (!vma)
 			break;
 
 		/*
-- 
2.23.0

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Keqian Zhu]

Hi Gavin,

On 2021/3/15 12:18, Gavin Shan wrote:
> find_vma_intersection() has been existing to search the intersected
> vma. This uses the function where it's applicable, to simplify the
> code.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kvm/mmu.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 84e70f953de6..286b603ed0d3 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>  	 *     +--------------------------------------------+
>  	 */
>  	do {
> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
> +		struct vm_area_struct *vma;
>  		hva_t vm_start, vm_end;
>  
> -		if (!vma || vma->vm_start >= reg_end)
> +		vma = find_vma_intersection(current->mm, hva, reg_end);
Nit: Keep a same style may be better(Assign vma when declare it).
Other looks good to me.

Thank,
Keqian


> +		if (!vma)
>  			break;
>  
>  		/*
> @@ -1330,10 +1331,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	 *     +--------------------------------------------+
>  	 */
>  	do {
> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
> +		struct vm_area_struct *vma;
>  		hva_t vm_start, vm_end;
>  
> -		if (!vma || vma->vm_start >= reg_end)
> +		vma = find_vma_intersection(current->mm, hva, reg_end);
> +		if (!vma)
>  			break;
>  
>  		/*
> 

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Gavin Shan]

Hi Keqian,

On 3/15/21 7:04 PM, Keqian Zhu wrote:
> On 2021/3/15 12:18, Gavin Shan wrote:
>> find_vma_intersection() has been existing to search the intersected
>> vma. This uses the function where it's applicable, to simplify the
>> code.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   arch/arm64/kvm/mmu.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 84e70f953de6..286b603ed0d3 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>>   	 *     +--------------------------------------------+
>>   	 */
>>   	do {
>> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
>> +		struct vm_area_struct *vma;
>>   		hva_t vm_start, vm_end;
>>   
>> -		if (!vma || vma->vm_start >= reg_end)
>> +		vma = find_vma_intersection(current->mm, hva, reg_end);
> Nit: Keep a same style may be better(Assign vma when declare it).
> Other looks good to me.
> 

Yeah, I agree. I will adjust the code in v2 and included your r-b.
Thanks for your time to review.

Thanks,
Gavin

  
>> +		if (!vma)
>>   			break;
>>   
>>   		/*
>> @@ -1330,10 +1331,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>   	 *     +--------------------------------------------+
>>   	 */
>>   	do {
>> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
>> +		struct vm_area_struct *vma;
>>   		hva_t vm_start, vm_end;
>>   
>> -		if (!vma || vma->vm_start >= reg_end)
>> +		vma = find_vma_intersection(current->mm, hva, reg_end);
>> +		if (!vma)
>>   			break;
>>   
>>   		/*
>>
> 

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Gavin Shan]

Hi Keqian,

On 3/15/21 8:42 PM, Gavin Shan wrote:
> On 3/15/21 7:04 PM, Keqian Zhu wrote:
>> On 2021/3/15 12:18, Gavin Shan wrote:
>>> find_vma_intersection() has been existing to search the intersected
>>> vma. This uses the function where it's applicable, to simplify the
>>> code.
>>>
>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>>> ---
>>>   arch/arm64/kvm/mmu.c | 10 ++++++----
>>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>>> index 84e70f953de6..286b603ed0d3 100644
>>> --- a/arch/arm64/kvm/mmu.c
>>> +++ b/arch/arm64/kvm/mmu.c
>>> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>>>        *     +--------------------------------------------+
>>>        */
>>>       do {
>>> -        struct vm_area_struct *vma = find_vma(current->mm, hva);
>>> +        struct vm_area_struct *vma;
>>>           hva_t vm_start, vm_end;
>>> -        if (!vma || vma->vm_start >= reg_end)
>>> +        vma = find_vma_intersection(current->mm, hva, reg_end);
>> Nit: Keep a same style may be better(Assign vma when declare it).
>> Other looks good to me.
>>
> 
> Yeah, I agree. I will adjust the code in v2 and included your r-b.
> Thanks for your time to review.
> 

After rechecking the code, I think it'd better to keep current style
because there is a follow-on validation on @vma. Keeping them together
seems a good idea. I think it wouldn't a big deal to you. So I will
keep current style with your r-b in v2.

	vma = find_vma_intersection(current->mm, hva, reg_end);
         if (!vma)
              break;
Thanks,
Gavin
  
>>> +        if (!vma)
>>>               break;
>>>           /*
>>> @@ -1330,10 +1331,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>>        *     +--------------------------------------------+
>>>        */
>>>       do {
>>> -        struct vm_area_struct *vma = find_vma(current->mm, hva);
>>> +        struct vm_area_struct *vma;
>>>           hva_t vm_start, vm_end;
>>> -        if (!vma || vma->vm_start >= reg_end)
>>> +        vma = find_vma_intersection(current->mm, hva, reg_end);
>>> +        if (!vma)
>>>               break;
>>>           /*
>>>
>>
> 

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Keqian Zhu]

Hi Gavin,

On 2021/3/16 11:52, Gavin Shan wrote:
> Hi Keqian,
> 
> On 3/15/21 8:42 PM, Gavin Shan wrote:
>> On 3/15/21 7:04 PM, Keqian Zhu wrote:
>>> On 2021/3/15 12:18, Gavin Shan wrote:
>>>> find_vma_intersection() has been existing to search the intersected
>>>> vma. This uses the function where it's applicable, to simplify the
>>>> code.
>>>>
>>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>>>> ---
>>>>   arch/arm64/kvm/mmu.c | 10 ++++++----
>>>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>>>> index 84e70f953de6..286b603ed0d3 100644
>>>> --- a/arch/arm64/kvm/mmu.c
>>>> +++ b/arch/arm64/kvm/mmu.c
>>>> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>>>>        *     +--------------------------------------------+
>>>>        */
>>>>       do {
>>>> -        struct vm_area_struct *vma = find_vma(current->mm, hva);
>>>> +        struct vm_area_struct *vma;
>>>>           hva_t vm_start, vm_end;
>>>> -        if (!vma || vma->vm_start >= reg_end)
>>>> +        vma = find_vma_intersection(current->mm, hva, reg_end);
>>> Nit: Keep a same style may be better(Assign vma when declare it).
>>> Other looks good to me.
>>>
>>
>> Yeah, I agree. I will adjust the code in v2 and included your r-b.
>> Thanks for your time to review.
>>
> 
> After rechecking the code, I think it'd better to keep current style
> because there is a follow-on validation on @vma. Keeping them together
> seems a good idea. I think it wouldn't a big deal to you. So I will
> keep current style with your r-b in v2.
Sure, both is OK. ;-)

Thanks,
Keqian
> 
>     vma = find_vma_intersection(current->mm, hva, reg_end);
>         if (!vma)
>              break;
> Thanks,
> Gavin
>  
>>>> +        if (!vma)
>>>>               break;
>>>>           /*
>>>> @@ -1330,10 +1331,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>>>        *     +--------------------------------------------+
>>>>        */
>>>>       do {
>>>> -        struct vm_area_struct *vma = find_vma(current->mm, hva);
>>>> +        struct vm_area_struct *vma;
>>>>           hva_t vm_start, vm_end;
>>>> -        if (!vma || vma->vm_start >= reg_end)
>>>> +        vma = find_vma_intersection(current->mm, hva, reg_end);
>>>> +        if (!vma)
>>>>               break;
>>>>           /*
>>>>
>>>
>>
> 
> .
> 

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Marc Zyngier]

On Mon, 15 Mar 2021 04:18:42 +0000,
Gavin Shan <gshan@redhat.com> wrote:
> 
> find_vma_intersection() has been existing to search the intersected
> vma. This uses the function where it's applicable, to simplify the
> code.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kvm/mmu.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 84e70f953de6..286b603ed0d3 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>  	 *     +--------------------------------------------+
>  	 */
>  	do {
> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
> +		struct vm_area_struct *vma;
>  		hva_t vm_start, vm_end;
>  
> -		if (!vma || vma->vm_start >= reg_end)
> +		vma = find_vma_intersection(current->mm, hva, reg_end);

For context, here's the definition of find_vma_intersection():

<quote>
static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
{
	struct vm_area_struct * vma = find_vma(mm,start_addr);

	if (vma && end_addr <= vma->vm_start)
		vma = NULL;
	return vma;
}
</quote>

It seems that there is a boundary issue in either the old code or the
new one in the case where (reg_end == vma->start).

Which one is which?

	M.

-- 
Without deviation from the norm, progress is not possible.

Re: [PATCH 2/4] KVM: arm64: Use find_vma_intersection()

[Gavin Shan]

Hi Marc,

On 3/15/21 7:52 PM, Marc Zyngier wrote:
> On Mon, 15 Mar 2021 04:18:42 +0000,
> Gavin Shan <gshan@redhat.com> wrote:
>>
>> find_vma_intersection() has been existing to search the intersected
>> vma. This uses the function where it's applicable, to simplify the
>> code.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   arch/arm64/kvm/mmu.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 84e70f953de6..286b603ed0d3 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -421,10 +421,11 @@ static void stage2_unmap_memslot(struct kvm *kvm,
>>   	 *     +--------------------------------------------+
>>   	 */
>>   	do {
>> -		struct vm_area_struct *vma = find_vma(current->mm, hva);
>> +		struct vm_area_struct *vma;
>>   		hva_t vm_start, vm_end;
>>   
>> -		if (!vma || vma->vm_start >= reg_end)
>> +		vma = find_vma_intersection(current->mm, hva, reg_end);
> 
> For context, here's the definition of find_vma_intersection():
> 
> <quote>
> static inline struct vm_area_struct * find_vma_intersection(struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
> {
> 	struct vm_area_struct * vma = find_vma(mm,start_addr);
> 
> 	if (vma && end_addr <= vma->vm_start)
> 		vma = NULL;
> 	return vma;
> }
> </quote>
> 
> It seems that there is a boundary issue in either the old code or the
> new one in the case where (reg_end == vma->start).
> 
> Which one is which?
> 

The old and new code is interchangeable, meaning "reg_end == vma->start"
is invalid in both cases. So if there is a boundary issue, the old and new
code should have same issue.

According to the code, "reg_end == vma->start" is invalid. So I don't see
there is a boundary issue. Hopefully, I don't miss anything :)

Thanks,
Gavin

[PATCH 3/4] KVM: arm64: Fix address check for memory slot

[Gavin Shan]

The last (IPA) page can't be specified when a new memory slot is
added. The error -EFAULT is returned when the memory slot is added
with the following parameters for the VM, which has 40-bits IPA
limit. The host has 4KB base page size. It's not correct because
the last (IPA) page is still usable.

   struct kvm_userspace_memory_region {
      __u32 slot;               /* 1            */
      __u32 flags;              /* 0            */
      __u64 guest_phys_addr;    /* 0xfffffff000 */
      __u64 memory_size;        /* 0x1000       */
      __u64 userspace_addr;
   };

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/kvm/mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 286b603ed0d3..a5a8ade9fde4 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1313,7 +1313,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	 * Prevent userspace from creating a memory region outside of the IPA
 	 * space addressable by the KVM guest IPA space.
 	 */
-	if (memslot->base_gfn + memslot->npages >=
+	if (memslot->base_gfn + memslot->npages >
 	    (kvm_phys_size(kvm) >> PAGE_SHIFT))
 		return -EFAULT;
 
-- 
2.23.0

Re: [PATCH 3/4] KVM: arm64: Fix address check for memory slot

[Keqian Zhu]

Hi Gavin,

FYI, this has been fixed by Marc in commit 262b003d059c.

Thanks,
Keqian

On 2021/3/15 12:18, Gavin Shan wrote:
> The last (IPA) page can't be specified when a new memory slot is
> added. The error -EFAULT is returned when the memory slot is added
> with the following parameters for the VM, which has 40-bits IPA
> limit. The host has 4KB base page size. It's not correct because
> the last (IPA) page is still usable.
> 
>    struct kvm_userspace_memory_region {
>       __u32 slot;               /* 1            */
>       __u32 flags;              /* 0            */
>       __u64 guest_phys_addr;    /* 0xfffffff000 */
>       __u64 memory_size;        /* 0x1000       */
>       __u64 userspace_addr;
>    };
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kvm/mmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 286b603ed0d3..a5a8ade9fde4 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1313,7 +1313,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  	 * Prevent userspace from creating a memory region outside of the IPA
>  	 * space addressable by the KVM guest IPA space.
>  	 */
> -	if (memslot->base_gfn + memslot->npages >=
> +	if (memslot->base_gfn + memslot->npages >
>  	    (kvm_phys_size(kvm) >> PAGE_SHIFT))
>  		return -EFAULT;
>  
> 

Re: [PATCH 3/4] KVM: arm64: Fix address check for memory slot

[Gavin Shan]

Hi Keqian,

On 3/15/21 6:33 PM, Keqian Zhu wrote:
> FYI, this has been fixed by Marc in commit 262b003d059c.
> 

Yeah, I didn't check 5.12.rc3 code where the issue has been
fixed. So please ignore this one and sorry for the noise.

Thanks,
Gavin
  
> On 2021/3/15 12:18, Gavin Shan wrote:
>> The last (IPA) page can't be specified when a new memory slot is
>> added. The error -EFAULT is returned when the memory slot is added
>> with the following parameters for the VM, which has 40-bits IPA
>> limit. The host has 4KB base page size. It's not correct because
>> the last (IPA) page is still usable.
>>
>>     struct kvm_userspace_memory_region {
>>        __u32 slot;               /* 1            */
>>        __u32 flags;              /* 0            */
>>        __u64 guest_phys_addr;    /* 0xfffffff000 */
>>        __u64 memory_size;        /* 0x1000       */
>>        __u64 userspace_addr;
>>     };
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   arch/arm64/kvm/mmu.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 286b603ed0d3..a5a8ade9fde4 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -1313,7 +1313,7 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>   	 * Prevent userspace from creating a memory region outside of the IPA
>>   	 * space addressable by the KVM guest IPA space.
>>   	 */
>> -	if (memslot->base_gfn + memslot->npages >=
>> +	if (memslot->base_gfn + memslot->npages >
>>   	    (kvm_phys_size(kvm) >> PAGE_SHIFT))
>>   		return -EFAULT;
>>   
>>
> 

[PATCH 4/4] KVM: arm64: Don't retrieve memory slot again in page fault handler

[Gavin Shan]

We needn't retrieve the memory slot again in user_mem_abort() because
the corresponding memory slot has been passed from the caller. This
would save some CPU cycles. For example, the time used to write 1GB
memory, which is backed by 2MB hugetlb pages and write-protected, is
dropped by 6.8% from 928ms to 864ms.

Signed-off-by: Gavin Shan <gshan@redhat.com>
---
 arch/arm64/kvm/mmu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index a5a8ade9fde4..4a4abcccfafb 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -846,7 +846,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	 */
 	smp_rmb();
 
-	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
+	pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
+				   write_fault, &writable, NULL);
 	if (pfn == KVM_PFN_ERR_HWPOISON) {
 		kvm_send_hwpoison_signal(hva, vma_shift);
 		return 0;
@@ -912,7 +913,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
 	/* Mark the page dirty only if the fault is handled successfully */
 	if (writable && !ret) {
 		kvm_set_pfn_dirty(pfn);
-		mark_page_dirty(kvm, gfn);
+		mark_page_dirty_in_slot(kvm, memslot, gfn);
 	}
 
 out_unlock:
-- 
2.23.0

Re: [PATCH 4/4] KVM: arm64: Don't retrieve memory slot again in page fault handler

[Keqian Zhu]

Hi Gavin,

On 2021/3/15 12:18, Gavin Shan wrote:
> We needn't retrieve the memory slot again in user_mem_abort() because
> the corresponding memory slot has been passed from the caller. This
I think you are right, though fault_ipa will be adjusted when we try to use block mapping,
the fault_supports_stage2_huge_mapping() makes sure we're not trying to map anything
not covered by the memslot, so the adjusted fault_ipa still belongs to the memslot.

> would save some CPU cycles. For example, the time used to write 1GB
> memory, which is backed by 2MB hugetlb pages and write-protected, is
> dropped by 6.8% from 928ms to 864ms.
> 
> Signed-off-by: Gavin Shan <gshan@redhat.com>
> ---
>  arch/arm64/kvm/mmu.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index a5a8ade9fde4..4a4abcccfafb 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -846,7 +846,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	 */
>  	smp_rmb();
>  
> -	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
> +	pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
> +				   write_fault, &writable, NULL);
It's better to update the code comments at same time.

>  	if (pfn == KVM_PFN_ERR_HWPOISON) {
>  		kvm_send_hwpoison_signal(hva, vma_shift);
>  		return 0;
> @@ -912,7 +913,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>  	/* Mark the page dirty only if the fault is handled successfully */
>  	if (writable && !ret) {
>  		kvm_set_pfn_dirty(pfn);
> -		mark_page_dirty(kvm, gfn);
> +		mark_page_dirty_in_slot(kvm, memslot, gfn);
>  	}
>  
>  out_unlock:
> 

Thanks,
Keqian.

Re: [PATCH 4/4] KVM: arm64: Don't retrieve memory slot again in page fault handler

[Gavin Shan]

Hi Keqian,

On 3/15/21 7:25 PM, Keqian Zhu wrote:
> On 2021/3/15 12:18, Gavin Shan wrote:
>> We needn't retrieve the memory slot again in user_mem_abort() because
>> the corresponding memory slot has been passed from the caller. This
> I think you are right, though fault_ipa will be adjusted when we try to use block mapping,
> the fault_supports_stage2_huge_mapping() makes sure we're not trying to map anything
> not covered by the memslot, so the adjusted fault_ipa still belongs to the memslot.
> 

Yeah, it's correct. Besides, the @logging_active is determined
based on the passed memory slot. It means user_mem_abort() can't
support memory range which spans multiple memory slot.

>> would save some CPU cycles. For example, the time used to write 1GB
>> memory, which is backed by 2MB hugetlb pages and write-protected, is
>> dropped by 6.8% from 928ms to 864ms.
>>
>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>> ---
>>   arch/arm64/kvm/mmu.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index a5a8ade9fde4..4a4abcccfafb 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -846,7 +846,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   	 */
>>   	smp_rmb();
>>   
>> -	pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
>> +	pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
>> +				   write_fault, &writable, NULL);
> It's better to update the code comments at same time.
> 

I guess you need some comments here? If so, I would add something
like below in v2:

	/*
	 * gfn_to_pfn_prot() can be used either with unnecessary overhead
	 * introduced to locate the memory slot because the memory slot is
	 * always fixed even @gfn is adjusted for huge pages.
	 */

>>   	if (pfn == KVM_PFN_ERR_HWPOISON) {
>>   		kvm_send_hwpoison_signal(hva, vma_shift);
>>   		return 0;
>> @@ -912,7 +913,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>   	/* Mark the page dirty only if the fault is handled successfully */
>>   	if (writable && !ret) {
>>   		kvm_set_pfn_dirty(pfn);
>> -		mark_page_dirty(kvm, gfn);
>> +		mark_page_dirty_in_slot(kvm, memslot, gfn);
>>   	}
>>   
>>   out_unlock:
>>

Thanks,
Gavin

Re: [PATCH 4/4] KVM: arm64: Don't retrieve memory slot again in page fault handler

[Keqian Zhu]

Hi Gavin,

On 2021/3/15 17:56, Gavin Shan wrote:
> Hi Keqian,
> 
> On 3/15/21 7:25 PM, Keqian Zhu wrote:
>> On 2021/3/15 12:18, Gavin Shan wrote:
>>> We needn't retrieve the memory slot again in user_mem_abort() because
>>> the corresponding memory slot has been passed from the caller. This
>> I think you are right, though fault_ipa will be adjusted when we try to use block mapping,
>> the fault_supports_stage2_huge_mapping() makes sure we're not trying to map anything
>> not covered by the memslot, so the adjusted fault_ipa still belongs to the memslot.
>>
> 
> Yeah, it's correct. Besides, the @logging_active is determined
> based on the passed memory slot. It means user_mem_abort() can't
> support memory range which spans multiple memory slot.
> 
>>> would save some CPU cycles. For example, the time used to write 1GB
>>> memory, which is backed by 2MB hugetlb pages and write-protected, is
>>> dropped by 6.8% from 928ms to 864ms.
>>>
>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>>> ---
>>>   arch/arm64/kvm/mmu.c | 5 +++--
>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>>> index a5a8ade9fde4..4a4abcccfafb 100644
>>> --- a/arch/arm64/kvm/mmu.c
>>> +++ b/arch/arm64/kvm/mmu.c
>>> @@ -846,7 +846,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>>        */
>>>       smp_rmb();
>>>   -    pfn = gfn_to_pfn_prot(kvm, gfn, write_fault, &writable);
>>> +    pfn = __gfn_to_pfn_memslot(memslot, gfn, false, NULL,
>>> +                   write_fault, &writable, NULL);
>> It's better to update the code comments at same time.
>>
> 
> I guess you need some comments here? If so, I would add something
> like below in v2:
> 
>     /*
>      * gfn_to_pfn_prot() can be used either with unnecessary overhead
>      * introduced to locate the memory slot because the memory slot is
>      * always fixed even @gfn is adjusted for huge pages.
>      */
Looks good.

See comments above "smp_rmb();", and actually my meaning is that we should change "gfn_to_pfn_prot"
to "__gfn_to_pfn_memslot" :)

Thanks,
Keqian

> 
>>>       if (pfn == KVM_PFN_ERR_HWPOISON) {
>>>           kvm_send_hwpoison_signal(hva, vma_shift);
>>>           return 0;
>>> @@ -912,7 +913,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>>       /* Mark the page dirty only if the fault is handled successfully */
>>>       if (writable && !ret) {
>>>           kvm_set_pfn_dirty(pfn);
>>> -        mark_page_dirty(kvm, gfn);
>>> +        mark_page_dirty_in_slot(kvm, memslot, gfn);
>>>       }
>>>     out_unlock:
>>>
> 
> Thanks,
> Gavin
> 
> 
> .
>