Hi Marc,
I think I have fully tested this patch. The next step is to do some restriction on
HVA in vfio module, so we can build block mapping for it with a higher probability.
Is there anything to improve? If not, could you apply it? ^_^
Thanks,
Keqian
On 2021/4/7 21:18, Marc Zyngier wrote:
> On Tue, 16 Mar 2021 13:43:38 +0000,
> Keqian Zhu <zhukeqian1@xxxxxxxxxx> wrote:
>>
>> The MMIO region of a device maybe huge (GB level), try to use
>> block mapping in stage2 to speedup both map and unmap.
>>
>> Compared to normal memory mapping, we should consider two more
>> points when try block mapping for MMIO region:
>>
>> 1. For normal memory mapping, the PA(host physical address) and
>> HVA have same alignment within PUD_SIZE or PMD_SIZE when we use
>> the HVA to request hugepage, so we don't need to consider PA
>> alignment when verifing block mapping. But for device memory
>> mapping, the PA and HVA may have different alignment.
>>
>> 2. For normal memory mapping, we are sure hugepage size properly
>> fit into vma, so we don't check whether the mapping size exceeds
>> the boundary of vma. But for device memory mapping, we should pay
>> attention to this.
>>
>> This adds device_rough_page_shift() to check these two points when
>> selecting block mapping size.
>>
>> Signed-off-by: Keqian Zhu <zhukeqian1@xxxxxxxxxx>
>> ---
>>
>> Mainly for RFC, not fully tested. I will fully test it when the
>> code logic is well accepted.
>>
>> ---
>> arch/arm64/kvm/mmu.c | 42 ++++++++++++++++++++++++++++++++++++++----
>> 1 file changed, 38 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index c59af5ca01b0..224aa15eb4d9 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -624,6 +624,36 @@ static void kvm_send_hwpoison_signal(unsigned long address, short lsb)
>> send_sig_mceerr(BUS_MCEERR_AR, (void __user *)address, lsb, current);
>> }
>>
>> +/*
>> + * Find a mapping size that properly insides the intersection of vma and
>> + * memslot. And hva and pa have the same alignment to this mapping size.
>> + * It's rough because there are still other restrictions, which will be
>> + * checked by the following fault_supports_stage2_huge_mapping().
>
> I don't think these restrictions make complete sense to me. If this is
> a PFNMAP VMA, we should use the biggest mapping size that covers the
> VMA, and not more than the VMA.
>
>> + */
>> +static short device_rough_page_shift(struct kvm_memory_slot *memslot,
>> + struct vm_area_struct *vma,
>> + unsigned long hva)
>> +{
>> + size_t size = memslot->npages * PAGE_SIZE;
>> + hva_t sec_start = max(memslot->userspace_addr, vma->vm_start);
>> + hva_t sec_end = min(memslot->userspace_addr + size, vma->vm_end);
>> + phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) + (hva - vma->vm_start);
>> +
>> +#ifndef __PAGETABLE_PMD_FOLDED
>> + if ((hva & (PUD_SIZE - 1)) == (pa & (PUD_SIZE - 1)) &&
>> + ALIGN_DOWN(hva, PUD_SIZE) >= sec_start &&
>> + ALIGN(hva, PUD_SIZE) <= sec_end)
>> + return PUD_SHIFT;
>> +#endif
>> +
>> + if ((hva & (PMD_SIZE - 1)) == (pa & (PMD_SIZE - 1)) &&
>> + ALIGN_DOWN(hva, PMD_SIZE) >= sec_start &&
>> + ALIGN(hva, PMD_SIZE) <= sec_end)
>> + return PMD_SHIFT;
>> +
>> + return PAGE_SHIFT;
>> +}
>> +
>> static bool fault_supports_stage2_huge_mapping(struct kvm_memory_slot *memslot,
>> unsigned long hva,
>> unsigned long map_size)
>> @@ -769,7 +799,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>> return -EFAULT;
>> }
>>
>> - /* Let's check if we will get back a huge page backed by hugetlbfs */
>> + /*
>> + * Let's check if we will get back a huge page backed by hugetlbfs, or
>> + * get block mapping for device MMIO region.
>> + */
>> mmap_read_lock(current->mm);
>> vma = find_vma_intersection(current->mm, hva, hva + 1);
>> if (unlikely(!vma)) {
>> @@ -780,11 +813,12 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>
>> if (is_vm_hugetlb_page(vma))
>> vma_shift = huge_page_shift(hstate_vma(vma));
>> + else if (vma->vm_flags & VM_PFNMAP)
>> + vma_shift = device_rough_page_shift(memslot, vma, hva);
>> else
>> vma_shift = PAGE_SHIFT;
>>
>> - if (logging_active ||
>> - (vma->vm_flags & VM_PFNMAP)) {
>> + if (logging_active) {
>> force_pte = true;
>> vma_shift = PAGE_SHIFT;
>
> But why should we downgrade to page-size mappings if logging? This is
> a device, and you aren't moving the device around, are you? Or is your
> device actually memory with a device mapping that you are trying to
> migrate?
>
>> }
>> @@ -855,7 +889,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>
>> if (kvm_is_device_pfn(pfn)) {
>> device = true;
>> - force_pte = true;
>> + force_pte = (vma_pagesize == PAGE_SIZE);
>> } else if (logging_active && !write_fault) {
>> /*
>> * Only actually map the page as writable if this was a write
>> --
>> 2.19.1
>>
>>
>
> Thanks,
>
> M.
>
