[PATCH v2] arm/arm64: KVM: map MMIO regions at creation time

[Ard Biesheuvel]

On 8 October 2014 13:56, Christoffer Dall <christoffer.dall at linaro.org> wrote:
> On Wed, Oct 08, 2014 at 01:05:10PM +0200, Ard Biesheuvel wrote:
>> There is really no point in faulting in memory regions page by page
>> if they are not backed by demand paged system RAM but by a linear
>> passthrough mapping of a host MMIO region.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>
>> I have omitted the other 5 patches of the series of which this was #6, as
>> Christoffer had indicated they could be merged separately.
>>
>> Changes since v1:
>> - move this logic to kvm_arch_prepare_memory_region() so it can be invoked
>>   when moving memory regions as well as when creating memory regions
>> - as we are reasoning about memory regions now instead of memslots, all data
>>   is retrieved from the 'mem' argument which points to a struct
>>   kvm_userspace_memory_region
>> - minor tweaks to the logic flow
>>
>> Again, compile tested only, due to lack of test cases.
>>
>>  arch/arm/kvm/mmu.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 51 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index fe53c3a30383..1403d9dc1190 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -1151,7 +1151,57 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>>                                  struct kvm_userspace_memory_region *mem,
>>                                  enum kvm_mr_change change)
>>  {
>> -     return 0;
>> +     hva_t hva = mem->userspace_addr;
>> +     hva_t reg_end = hva + mem->memory_size;
>> +     phys_addr_t gpa = mem->guest_phys_addr;
>> +     int ret = 0;
>> +
>> +     if (change != KVM_MR_CREATE && change != KVM_MR_MOVE)
>> +             return 0;
>> +
>> +     /*
>> +      * A memory region could potentially cover multiple VMAs, so iterate
>> +      * over all of them to find out if we can map any of them right now.
>> +      *
>> +      *     +--------------------------------------------+
>> +      * +---+---------+-------------------+--------------+----+
>> +      * |   : VMA 1   |       VMA 2       |       VMA 3  :    |
>> +      * +---+---------+-------------------+--------------+----+
>> +      *     |               memory region                |
>> +      *     +--------------------------------------------+
>> +      */
>> +     do {
>> +             struct vm_area_struct *vma = find_vma(current->mm, hva);
>> +             hva_t vm_end;
>> +
>> +             if (!vma || vma->vm_start > hva) {
>> +                     ret = -EFAULT;
>> +                     break;
>> +             }
>> +
>> +             vm_end = min(reg_end, vma->vm_end);
>> +
>> +             if (vma->vm_flags & VM_PFNMAP) {
>> +                     phys_addr_t pa = (vma->vm_pgoff << PAGE_SHIFT) + hva -
>> +                                      vma->vm_start;
>> +                     bool writable = (vma->vm_flags & VM_WRITE) &&
>> +                                     !(mem->flags & KVM_MEM_READONLY);
>> +
>> +                     ret = kvm_phys_addr_ioremap(kvm, gpa, pa, vm_end - hva,
>> +                                                 writable);
>> +                     if (ret)
>> +                             break;
>> +             }
>> +             gpa += vm_end - hva;
>> +             hva = vm_end;
>> +     } while (hva < reg_end);
>> +
>> +     if (ret) {
>> +             spin_lock(&kvm->mmu_lock);
>> +             unmap_stage2_range(kvm, mem->guest_phys_addr, mem->memory_size);
>> +             spin_unlock(&kvm->mmu_lock);
>> +     }
>> +     return ret;
>>  }
>>
>>  void kvm_arch_free_memslot(struct kvm *kvm, struct kvm_memory_slot *free,
>
> If userspace moves the memory region in the guest IPA, then when are we
> unmapping the old IPA region?  Should we not do this before we create
> the new mappings (which may potentially overlap with the old one)?
>

You are right: I will move this logic to
kvm_arch_commit_memory_region() instead so we can execute it after the
unmap() has occurred.

-- 
Ard.