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

[Yan Zhao <yan.y.zhao@intel.com>]

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.
> 
> Paolo

hi Paolo

Thanks and I'll try it tomorrow and let you know the result.
But may I know why it cannot simply be like below?

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;