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


From: Yan Zhao
Subject: Re: [Qemu-devel] [PATCH] memory: do not do out of bound notification
Date: Fri, 21 Jun 2019 03:57:13 -0400
User-agent: Mutt/1.9.4 (2018-02-28)

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,
>
hi Peter and Paolo,
I can help test it next week. Didn't manage to find a time for it today.

Thanks
Yan

> ------------------------------------------------------------
> 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



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