Re: [Xen-devel] [PATCH] VT-d: fix RMRR handling

["Zhang, Xiantao" <xiantao.zhang@xxxxxxxxx>]

Jan, my comments embedded, thanks!

> Removing mapped RMRR tracking structures in dma_pte_clear_one() is wrong
> for two reasons: First, these regions may cover more than a single page. And
> second, multiple devices (and hence multiple devices assigned to any
> particular guest) may share a single RMRR (whether assigning such devices to
> distinct guests is a safe thing to do is another question).

Agree, this is a real issue as you described

> Therefore move the removal of the tracking structures into the counterpart
> function to the one doing the insertion - intel_iommu_remove_device(), and
> add a reference count to the tracking structure.

Adding a reference count is a good idea, but from the logic, seems you are 
adding a global counter for each rmrr? 
In theory, one rmrr may be mapped for multiple devices in multiple domains, 
global counter for once rmrr is not enough. 
Maybe we need to per-domain counter there ? 

> Further, for the handling of the mappings of the respective memory regions to
> be correct, RMRRs must not overlap. Add a respective check to
> acpi_parse_one_rmrr().
> 
> And finally, with all of this being VT-d specific, move the cleanup of the 
> list as
> well as the structure type definition where it belongs - in VT-d specific 
> rather
> than IOMMU generic code.
> 
> Note that this doesn't address yet another issue associated with RMRR
> handling: The purpose of the RMRRs as well as the way the respective IOMMU
> page table mappings get inserted both suggest that these regions would need
> to be marked E820_RESERVED in all (HVM?) guests' memory maps, yet nothing
> like this is being done in hvmloader. (For PV guests this would also seem to 
> be
> necessary, but may conflict with PV guests possibly assuming there to be just 
> a
> single E820 entry representing all of its RAM.)

Yes, this is really a pending issue there, and we need to find a clean way to 
handle it. 


> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/drivers/passthrough/vtd/dmar.c
> +++ b/xen/drivers/passthrough/vtd/dmar.c
> @@ -580,6 +580,16 @@ acpi_parse_one_rmrr(struct acpi_dmar_hea
>      if ( (ret = acpi_dmar_check_length(header, sizeof(*rmrr))) != 0 )
>          return ret;
> 
> +    list_for_each_entry(rmrru, &acpi_rmrr_units, list)
> +       if ( base_addr <= rmrru->end_address && rmrru->base_address <=
> end_addr )
> +       {
> +           printk(XENLOG_ERR VTDPREFIX
> +                  "Overlapping RMRRs [%"PRIx64",%"PRIx64"] and
> [%"PRIx64",%"PRIx64"]\n",
> +                  rmrru->base_address, rmrru->end_address,
> +                  base_addr, end_addr);
> +           return -EEXIST;
> +       }
> +
>      /* This check is here simply to detect when RMRR values are
>       * not properly represented in the system memory map and
>       * inform the user
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -412,9 +412,8 @@ static int iommu_populate_page_table(str  void
> iommu_domain_destroy(struct domain *d)  {
>      struct hvm_iommu *hd  = domain_hvm_iommu(d);
> -    struct list_head *ioport_list, *rmrr_list, *tmp;
> +    struct list_head *ioport_list, *tmp;
>      struct g2m_ioport *ioport;
> -    struct mapped_rmrr *mrmrr;
> 
>      if ( !iommu_enabled || !hd->platform_ops )
>          return;
> @@ -428,13 +427,6 @@ void iommu_domain_destroy(struct domain
>          list_del(&ioport->list);
>          xfree(ioport);
>      }
> -
> -    list_for_each_safe ( rmrr_list, tmp, &hd->mapped_rmrrs )
> -    {
> -        mrmrr = list_entry(rmrr_list, struct mapped_rmrr, list);
> -        list_del(&mrmrr->list);
> -        xfree(mrmrr);
> -    }
>  }
> 
>  int iommu_map_page(struct domain *d, unsigned long gfn, unsigned long
> mfn,
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -43,6 +43,12 @@
>  #include "vtd.h"
>  #include "../ats.h"
> 
> +struct mapped_rmrr {
> +    struct list_head list;
> +    u64 base, end;
> +    unsigned int count;
> +};
> +
>  /* Possible unfiltered LAPIC/MSI messages from untrusted sources? */
> bool_t __read_mostly untrusted_msi;
> 
> @@ -620,7 +626,6 @@ static void dma_pte_clear_one(struct dom
>      struct hvm_iommu *hd = domain_hvm_iommu(domain);
>      struct dma_pte *page = NULL, *pte = NULL;
>      u64 pg_maddr;
> -    struct mapped_rmrr *mrmrr;
> 
>      spin_lock(&hd->mapping_lock);
>      /* get last level pte */
> @@ -649,21 +654,6 @@ static void dma_pte_clear_one(struct dom
>          __intel_iommu_iotlb_flush(domain, addr >> PAGE_SHIFT_4K, 1, 1);
> 
>      unmap_vtd_domain_page(page);
> -
> -    /* if the cleared address is between mapped RMRR region,
> -     * remove the mapped RMRR
> -     */
> -    spin_lock(&hd->mapping_lock);
> -    list_for_each_entry ( mrmrr, &hd->mapped_rmrrs, list )
> -    {
> -        if ( addr >= mrmrr->base && addr <= mrmrr->end )
> -        {
> -            list_del(&mrmrr->list);
> -            xfree(mrmrr);
> -            break;
> -        }
> -    }
> -    spin_unlock(&hd->mapping_lock);
>  }
> 
>  static void iommu_free_pagetable(u64 pt_maddr, int level) @@ -1704,10
> +1694,17 @@ static int reassign_device_ownership(  void
> iommu_domain_teardown(struct domain *d)  {
>      struct hvm_iommu *hd = domain_hvm_iommu(d);
> +    struct mapped_rmrr *mrmrr, *tmp;
> 
>      if ( list_empty(&acpi_drhd_units) )
>          return;
> 
> +    list_for_each_entry_safe ( mrmrr, tmp, &hd->mapped_rmrrs, list )
> +    {
> +        list_del(&mrmrr->list);
> +        xfree(mrmrr);
> +    }
> +
>      if ( iommu_use_hap_pt(d) )
>          return;
> 
> @@ -1852,14 +1849,17 @@ static int rmrr_identity_mapping(struct
>      ASSERT(rmrr->base_address < rmrr->end_address);
> 
>      /*
> -     * No need to acquire hd->mapping_lock, as the only theoretical race is
> -     * with the insertion below (impossible due to holding pcidevs_lock).
> +     * No need to acquire hd->mapping_lock: Both insertion and removal
> +     * get done while holding pcidevs_lock.
>       */
>      list_for_each_entry( mrmrr, &hd->mapped_rmrrs, list )
>      {
>          if ( mrmrr->base == rmrr->base_address &&
>               mrmrr->end == rmrr->end_address )
> +        {
> +            ++mrmrr->count;
>              return 0;
> +        }
>      }
> 
>      base = rmrr->base_address & PAGE_MASK_4K; @@ -1880,9 +1880,8 @@
> static int rmrr_identity_mapping(struct
>          return -ENOMEM;
>      mrmrr->base = rmrr->base_address;
>      mrmrr->end = rmrr->end_address;
> -    spin_lock(&hd->mapping_lock);
> +    mrmrr->count = 1;
>      list_add_tail(&mrmrr->list, &hd->mapped_rmrrs);
> -    spin_unlock(&hd->mapping_lock);
> 
>      return 0;
>  }
> @@ -1944,17 +1943,50 @@ static int intel_iommu_remove_device(u8
>      if ( !pdev->domain )
>          return -EINVAL;
> 
> -    /* If the device belongs to dom0, and it has RMRR, don't remove it
> -     * from dom0, because BIOS may use RMRR at booting time.
> -     */
> -    if ( pdev->domain->domain_id == 0 )
> +    for_each_rmrr_device ( rmrr, bdf, i )
>      {
> -        for_each_rmrr_device ( rmrr, bdf, i )
> +        struct hvm_iommu *hd;
> +        struct mapped_rmrr *mrmrr, *tmp;
> +
> +        if ( rmrr->segment != pdev->seg ||
> +             PCI_BUS(bdf) != pdev->bus ||
> +             PCI_DEVFN2(bdf) != devfn )
> +            continue;
> +
> +        /*
> +         * If the device belongs to dom0, and it has RMRR, don't remove
> +         * it from dom0, because BIOS may use RMRR at booting time.
> +         */
> +        if ( is_hardware_domain(pdev->domain) )
> +            return 0;
> +
> +        hd = domain_hvm_iommu(pdev->domain);
> +
> +        /*
> +         * No need to acquire hd->mapping_lock: Both insertion and
> removal
> +         * get done while holding pcidevs_lock.
> +         */
> +        ASSERT(spin_is_locked(&pcidevs_lock));
> +        list_for_each_entry_safe ( mrmrr, tmp, &hd->mapped_rmrrs, list
> + )
>          {
> -            if ( rmrr->segment == pdev->seg &&
> -                 PCI_BUS(bdf) == pdev->bus &&
> -                 PCI_DEVFN2(bdf) == devfn )
> -                return 0;
> +            unsigned long base_pfn, end_pfn;
> +
> +            if ( rmrr->base_address != mrmrr->base ||
> +                 rmrr->end_address != mrmrr->end ||
> +                 --mrmrr->count )
> +                continue;
> +
> +            base_pfn = (mrmrr->base & PAGE_MASK_4K) >>
> PAGE_SHIFT_4K;
> +            end_pfn = PAGE_ALIGN_4K(mrmrr->end) >> PAGE_SHIFT_4K;
> +            while ( base_pfn < end_pfn )
> +            {
> +                if ( intel_iommu_unmap_page(pdev->domain, base_pfn) )
> +                    return -ENXIO;
> +                base_pfn++;
> +            }
> +
> +            list_del(&mrmrr->list);
> +            xfree(mrmrr);
>          }
>      }
> 
> --- a/xen/include/xen/hvm/iommu.h
> +++ b/xen/include/xen/hvm/iommu.h
> @@ -29,12 +29,6 @@ struct g2m_ioport {
>      unsigned int np;
>  };
> 
> -struct mapped_rmrr {
> -    struct list_head list;
> -    u64 base;
> -    u64 end;
> -};
> -
>  struct hvm_iommu {
>      u64 pgd_maddr;                 /* io page directory machine
> address */
>      spinlock_t mapping_lock;       /* io page table lock */
> 


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