Re: [Qemu-devel] [PATCH] memory: do not do out of bound notification

[Paolo Bonzini]

On 20/06/19 12:57, Yan Zhao wrote:
> On Thu, Jun 20, 2019 at 04:35:29PM +0800, Paolo Bonzini wrote:
>> On 20/06/19 06:02, Peter Xu wrote:
>>> Seems workable, to be explicit - we can even cut it into chunks with
>>> different size to be efficient.
>>
>> Yes, this is not hard (completely untested):
>>
>> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
>> index 44b1231157..541538bc6c 100644
>> --- a/hw/i386/intel_iommu.c
>> +++ b/hw/i386/intel_iommu.c
>> @@ -3388,39 +3388,34 @@ static void vtd_address_space_unmap(VTDAddressSpace 
>> *as, IOMMUNotifier *n)
>>      }
>>  
>>      assert(start <= end);
>> -    size = end - start;
>> +    while (end > start) {
>> +        size = end - start;
>> +        /* Only keep the lowest bit of either size or start.  */
>> +        size = MIN(size & -size, start & -start);
>> +        /* Should not happen, but limit to address width too just in case */
>> +        size = MIN(size, 1ULL << s->aw_bits);
>>  
>> -    if (ctpop64(size) != 1) {
>> -        /*
>> -         * This size cannot format a correct mask. Let's enlarge it to
>> -         * suite the minimum available mask.
>> -         */
>> -        int n = 64 - clz64(size);
>> -        if (n > s->aw_bits) {
>> -            /* should not happen, but in case it happens, limit it */
>> -            n = s->aw_bits;
>> -        }
>> -        size = 1ULL << n;
>> -    }
>> +        assert((start & (size - 1)) == 0);
>>  
>> -    entry.target_as = &address_space_memory;
>> -    /* Adjust iova for the size */
>> -    entry.iova = n->start & ~(size - 1);
>> -    /* This field is meaningless for unmap */
>> -    entry.translated_addr = 0;
>> -    entry.perm = IOMMU_NONE;
>> -    entry.addr_mask = size - 1;
>> +        entry.target_as = &address_space_memory;
>> +        entry.iova = start;
>> +        /* This field is meaningless for unmap */
>> +        entry.translated_addr = 0;
>> +        entry.perm = IOMMU_NONE;
>> +        entry.addr_mask = size - 1;
>>  
>> -    trace_vtd_as_unmap_whole(pci_bus_num(as->bus),
>> -                             VTD_PCI_SLOT(as->devfn),
>> -                             VTD_PCI_FUNC(as->devfn),
>> -                             entry.iova, size);
>> +        trace_vtd_as_unmap_whole(pci_bus_num(as->bus),
>> +                                 VTD_PCI_SLOT(as->devfn),
>> +                                 VTD_PCI_FUNC(as->devfn),
>> +                                 entry.iova, size);
>>  
>> -    map.iova = entry.iova;
>> -    map.size = entry.addr_mask;
>> -    iova_tree_remove(as->iova_tree, &map);
>> +        map.iova = entry.iova;
>> +        map.size = entry.addr_mask;
>> +        iova_tree_remove(as->iova_tree, &map);
>>  
>> -    memory_region_notify_one(n, &entry);
>> +        memory_region_notify_one(n, &entry);
>> +        start += size;
>> +    }
>>  }
>>  
>>  static void vtd_address_space_unmap_all(IntelIOMMUState *s)
>>
>>
>> Yan,
>>
>> if something like this works for you, let me know and I will submit it
>> as a proper patch.
> 
> Thanks and I'll try it tomorrow and let you know the result.
> But may I know why it cannot simply be like below?

Because the API is that addr_mask is a power of two minus 1.

Paolo

> Thanks
> Yan
> 
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index b0d8a1c..2956db6 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -3374,7 +3374,6 @@ static void vtd_address_space_unmap(VTDAddressSpace 
> *as, IOMMUNotifier *n)
>      IntelIOMMUState *s = as->iommu_state;
>      DMAMap map;
> 
>      /*
>       * Note: all the codes in this function has a assumption that IOVA
>       * bits are no more than VTD_MGAW bits (which is restricted by
> @@ -3392,23 +3391,8 @@ static void vtd_address_space_unmap(VTDAddressSpace 
> *as, IOMMUNotifier *n)
>      assert(start <= end);
>      size = end - start;
> 
> -    if (ctpop64(size) != 1) {
> -        /*
> -         * This size cannot format a correct mask. Let's enlarge it to
> -         * suite the minimum available mask.
> -         */
> -        int n = 64 - clz64(size);
> -        if (n > s->aw_bits) {
> -            /* should not happen, but in case it happens, limit it */
> -            n = s->aw_bits;
> -        }
> -        size = 1ULL << n;
> -    }
> -
> -
>      entry.target_as = &address_space_memory;
> -    /* Adjust iova for the size */
> -    entry.iova = n->start & ~(size - 1);
> +    entry.iova = n->start;
>      /* This field is meaningless for unmap */
>      entry.translated_addr = 0;
>      entry.perm = IOMMU_NONE;
> 
> 
>