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

[Peter Xu]

On Thu, Jun 20, 2019 at 10:35:29AM +0200, 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);

I feel like this can be problematic.  I'm imaging:

start=0x1000_0000, size=0x1000_1000

This will get size=0x1000 but actually we can do size=0x1000_0000 as
the first.

> +        /* 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;

(some of the fields can be moved out of loop because they are
 constants)

>  
> -    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);

Can move this out because this is a trace only so we don't have
restriction on mask?

>  
> -    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);

Same here?

>  
> -    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

Since during review I'm thinking how to generate a correct sequence of
these masks... here's my try below with above issues fixed... :)

I've tried compile but not tested.  Yan can test it, or I can do it
too tomorrow after I find some machines.

Thanks,

------------------------------------------------------------
diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 44b1231157..cfbd225f0a 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -3363,11 +3363,32 @@ VTDAddressSpace *vtd_find_add_as(IntelIOMMUState *s, 
PCIBus *bus, int devfn)
     return vtd_dev_as;
 }

+static uint64_t vtd_get_next_mask(uint64_t start, uint64_t size, int gaw)
+{
+    /* Tries to find smallest mask from start first */
+    uint64_t rmask = start & -start, max_mask = 1ULL << gaw;
+
+    assert(size && gaw > 0 && gaw < 64);
+
+    /* Zero start, or too big */
+    if (!rmask || rmask > max_mask) {
+        rmask = max_mask;
+    }
+
+    /* If the start mask worked, then use it */
+    if (rmask <= size) {
+        return rmask;
+    }
+
+    /* Find the largest page mask from size */
+    return 1ULL << (63 - clz64(size));
+}
+
 /* Unmap the whole range in the notifier's scope. */
 static void vtd_address_space_unmap(VTDAddressSpace *as, IOMMUNotifier *n)
 {
     IOMMUTLBEntry entry;
-    hwaddr size;
+    hwaddr size, remain;
     hwaddr start = n->start;
     hwaddr end = n->end;
     IntelIOMMUState *s = as->iommu_state;
@@ -3388,39 +3409,28 @@ 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;
-    }
-
+    size = remain = end - start;
     entry.target_as = &address_space_memory;
-    /* Adjust iova for the size */
-    entry.iova = n->start & ~(size - 1);
+    entry.perm = IOMMU_NONE;
     /* This field is meaningless for unmap */
     entry.translated_addr = 0;
-    entry.perm = IOMMU_NONE;
-    entry.addr_mask = size - 1;
+
+    while (remain) {
+        uint64_t mask = vtd_get_next_mask(start, remain, s->aw_bits);
+
+        entry.iova = start;
+        entry.addr_mask = mask - 1;
+        memory_region_notify_one(n, &entry);
+    }

     trace_vtd_as_unmap_whole(pci_bus_num(as->bus),
                              VTD_PCI_SLOT(as->devfn),
                              VTD_PCI_FUNC(as->devfn),
-                             entry.iova, size);
+                             n->start, size);

-    map.iova = entry.iova;
-    map.size = entry.addr_mask;
+    map.iova = n->start;
+    map.size = size;
     iova_tree_remove(as->iova_tree, &map);
-
-    memory_region_notify_one(n, &entry);
 }

 static void vtd_address_space_unmap_all(IntelIOMMUState *s)
------------------------------------------------------------

Regards,

-- 
Peter Xu