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

[Peter Xu <peterx@redhat.com>]

On Mon, Jun 24, 2019 at 01:22:55AM -0400, Yan Zhao wrote:
> On Thu, Jun 20, 2019 at 09:04:43PM +0800, Peter Xu wrote:
> > On Thu, Jun 20, 2019 at 08:59:55PM +0800, Peter Xu wrote:
> > > 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);
> > 
> > Sorry, I at least missed these lines:
> > 
> >            start += mask;
> >            remain -= mask;
> > 
> > > +    }
> > > 
> > >      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
> > 
> > Regards,
> > 
> > -- 
> > Peter Xu
> 
> hi Peter and Paolo,
> I tested with code and it's fine in my side.
> It's base on your version with some minor modifications, such as size is
> now  (end - start + 1) now.
> Thanks
> Yan

Hi, Yan,

Thanks for testing the patches.  I think below change [1] is not
related to the problem so I tend to split it out.  For [2] I'll change
to an assertion if you won't disagree.  I'll reorganize the patches
and post a formal version with proper authorships soon.

Thanks,

> 
> +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;
> @@ -3380,48 +3398,46 @@ static void vtd_address_space_unmap(VTDAddressSpace *as, IOMMUNotifier *n)
>       * VT-d spec), otherwise we need to consider overflow of 64 bits.
>       */
> 
> -    if (end > VTD_ADDRESS_SIZE(s->aw_bits)) {
> +    if (end > VTD_ADDRESS_SIZE(s->aw_bits) - 1) {
>          /*
>           * Don't need to unmap regions that is bigger than the whole
>           * VT-d supported address space size
>           */
> -        end = VTD_ADDRESS_SIZE(s->aw_bits);
> +        end = VTD_ADDRESS_SIZE(s->aw_bits) - 1;

[1]

>      }
> 
>      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 + 1;
> 
>      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 >= VTD_PAGE_SIZE) {
> +        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);
> +        start += mask;
> +        remain -= mask;
> +    }
> +
> +    if (remain) {
> +        warn_report("Unmapping unaligned range %lx-%lx", start, end);

[2]

> +    }
> 
>      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;
> +                             n->start, size);
> +    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)
> --
> 2.7.4
> 
> 
> 

Regards,

-- 
Peter Xu