Re: [Qemu-devel] [PATCH 2/2] intel_iommu: Fix unexpected unmaps during global unmap

[Yan Zhao]

On Mon, Jun 24, 2019 at 02:37:33PM +0800, Peter Xu wrote:
> From: Paolo Bonzini <address@hidden>
> 
> This is an replacement work of Yan Zhao's patch:
> 
> https://www.mail-archive.com/address@hidden/msg625340.html
> 
> vtd_address_space_unmap() will do proper page mask alignment to make
> sure each IOTLB message will have correct masks for notification
> messages (2^N-1), but sometimes it can be expanded to even supercede
> the registered range.  That could lead to unexpected UNMAP of already
> mapped regions in some other notifiers.
> 
> Instead of doing mindless expension of the start address and address
> mask, we split the range into smaller ones and guarantee that each
> small range will have correct masks (2^N-1) and at the same time we
> should also try our best to generate as less IOTLB messages as
> possible.
> 
> Reported-by: Yan Zhao <address@hidden>
> Signed-off-by: Paolo Bonzini <address@hidden>
> [peterx: fixup mask generation algos and other touchups, introduce
>  vtd_get_next_mask(), write commit message]
> Signed-off-by: Peter Xu <address@hidden>
> ---
>  hw/i386/intel_iommu.c | 70 +++++++++++++++++++++++++++----------------
>  1 file changed, 44 insertions(+), 26 deletions(-)
> 
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 719ce19ab3..39cedf73b8 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -3363,11 +3363,31 @@ 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 +3408,37 @@ static void vtd_address_space_unmap(VTDAddressSpace 
> *as, IOMMUNotifier *n)
>      }
>  
>      assert(start <= end);
> -    size = end - start;
> +    size = remain = end - start + 1;
>  
> -    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;
> +    while (remain > 0) {
hi 
I think here remain should still be "remain >= VTD_PAGE_SIZE"
because we cannot unmap entry less than PAGE_SIZE.

> +        IOMMUTLBEntry entry;
> +        uint64_t mask = vtd_get_next_mask(start, remain, s->aw_bits);
> +
> +        assert(mask);
> +

> +        entry.iova = start;
> +        entry.addr_mask = mask - 1;
> +        entry.target_as = &address_space_memory;
> +        entry.perm = IOMMU_NONE;
> +        /* This field is meaningless for unmap */
> +        entry.translated_addr = 0;
> +
> +        memory_region_notify_one(n, &entry);
> +
> +        start += mask;
> +        remain -= mask;
>      }
Add assert(remain) here?

>  
> -    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;
> +    assert(!remain);
>  
>      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)
> -- 
> 2.21.0
>