Re: [Qemu-devel] [PATCH v5 07/11] vfio: Add guest side IOMMU support

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 03/20/2014 06:57 AM, Alex Williamson wrote:
> On Wed, 2014-03-12 at 16:52 +1100, Alexey Kardashevskiy wrote:
>> From: David Gibson <david@gibson.dropbear.id.au>
>>
>> This patch uses the new IOMMU notifiers to allow VFIO pass through devices
>> to work with guest side IOMMUs, as long as the host-side VFIO iommu has
>> sufficient capability and granularity to match the guest side. This works
>> by tracking all map and unmap operations on the guest IOMMU using the
>> notifiers, and mirroring them into VFIO.
>>
>> There are a number of FIXMEs, and the scheme involves rather more notifier
>> structures than I'd like, but it should make for a reasonable proof of
>> concept.
>>
>> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>>
>> ---
>> Changes:
>> v4:
>> * fixed list objects naming
>> * vfio_listener_region_add() reworked to call memory_region_ref() from one
>> place only, it is also easier to review the changes
>> * fixes boundary check not to fail on sections == 2^64 bytes,
>> the "vfio: Fix debug output for int128 values" patch is required;
>> this obsoletes the "[PATCH v3 0/3] vfio: fixes for better support
>> for 128 bit memory section sizes" patch proposal
>> ---
>>  hw/misc/vfio.c | 126 ++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>>  1 file changed, 120 insertions(+), 6 deletions(-)
>>
>> diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
>> index 038010b..4f6f5da 100644
>> --- a/hw/misc/vfio.c
>> +++ b/hw/misc/vfio.c
>> @@ -159,10 +159,18 @@ typedef struct VFIOContainer {
>>          };
>>          void (*release)(struct VFIOContainer *);
>>      } iommu_data;
>> +    QLIST_HEAD(, VFIOGuestIOMMU) giommu_list;
>>      QLIST_HEAD(, VFIOGroup) group_list;
>>      QLIST_ENTRY(VFIOContainer) next;
>>  } VFIOContainer;
>>  
>> +typedef struct VFIOGuestIOMMU {
>> +    VFIOContainer *container;
>> +    MemoryRegion *iommu;
>> +    Notifier n;
>> +    QLIST_ENTRY(VFIOGuestIOMMU) giommu_next;
>> +} VFIOGuestIOMMU;
>> +
>>  /* Cache of MSI-X setup plus extra mmap and memory region for split BAR map */
>>  typedef struct VFIOMSIXInfo {
>>      uint8_t table_bar;
>> @@ -2241,8 +2249,9 @@ static int vfio_dma_map(VFIOContainer *container, hwaddr iova,
>>  
>>  static bool vfio_listener_skipped_section(MemoryRegionSection *section)
>>  {
>> -    return !memory_region_is_ram(section->mr) ||
>> -           /*
>> +    return (!memory_region_is_ram(section->mr) &&
>> +            !memory_region_is_iommu(section->mr)) ||
>> +        /*
> 
> White space damage
> 
>>              * Sizing an enabled 64-bit BAR can cause spurious mappings to
>>              * addresses in the upper part of the 64-bit address space.  These
>>              * are never accessed by the CPU and beyond the address width of
>> @@ -2251,6 +2260,61 @@ static bool vfio_listener_skipped_section(MemoryRegionSection *section)
>>             section->offset_within_address_space & (1ULL << 63);
>>  }
>>  
>> +static void vfio_iommu_map_notify(Notifier *n, void *data)
>> +{
>> +    VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
>> +    VFIOContainer *container = giommu->container;
>> +    IOMMUTLBEntry *iotlb = data;
>> +    MemoryRegion *mr;
>> +    hwaddr xlat;
>> +    hwaddr len = iotlb->addr_mask + 1;
>> +    void *vaddr;
>> +    int ret;
>> +
>> +    DPRINTF("iommu map @ %"HWADDR_PRIx" - %"HWADDR_PRIx"\n",
>> +            iotlb->iova, iotlb->iova + iotlb->addr_mask);
>> +
>> +    /*
>> +     * The IOMMU TLB entry we have just covers translation through
>> +     * this IOMMU to its immediate target.  We need to translate
>> +     * it the rest of the way through to memory.
>> +     */
>> +    mr = address_space_translate(&address_space_memory,
>> +                                 iotlb->translated_addr,
>> +                                 &xlat, &len, iotlb->perm & IOMMU_WO);
> 
> Write-only?  Is this supposed to be read-write to mask just 2 bits?


The last parameter of address_space_translate() bool is_write. So I do not
really understand the problem here.


>> +    if (!memory_region_is_ram(mr)) {
>> +        DPRINTF("iommu map to non memory area %"HWADDR_PRIx"\n",
>> +                xlat);
>> +        return;
>> +    }
>> +    if (len & iotlb->addr_mask) {
>> +        DPRINTF("iommu has granularity incompatible with target AS\n");
> 
> Is this possible?  Assuming len is initially a power-of-2, would the
> translate function change it?  Maybe worth a comment to explain.


Oh. address_space_translate() actually changes @len to min(len,
TARGET_PAGE_SIZE) and TARGET_PAGE_SIZE is hardcoded to 4K. So far it was ok
but lately I have been implementing a huge DMA window (plus one
sPAPRTCETable and one VFIOGuestIOMMU objects) which currently operates with
16MB pages (can do 64K pages too) and now this "granularity incompatible"
is happening.

I disabled that check but I need to think of better fix...

Adding Paolo to cc, may be he picks the context and gives good piece of
advise :)



> 
>> +        return;
>> +    }
>> +
>> +    vaddr = memory_region_get_ram_ptr(mr) + xlat;
> 
> This lookup isn't free and the unmap path doesn't need it, maybe move
> the variable and lookup into the first branch below?
> 
>> +
>> +    if (iotlb->perm != IOMMU_NONE) {
>> +        ret = vfio_dma_map(container, iotlb->iova,
>> +                           iotlb->addr_mask + 1, vaddr,
>> +                           !(iotlb->perm & IOMMU_WO) || mr->readonly);
>> +        if (ret) {
>> +            error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
>> +                         "0x%"HWADDR_PRIx", %p) = %d (%m)",
>> +                         container, iotlb->iova,
>> +                         iotlb->addr_mask + 1, vaddr, ret);
>> +        }
>> +    } else {
>> +        ret = vfio_dma_unmap(container, iotlb->iova, iotlb->addr_mask + 1);
>> +        if (ret) {
>> +            error_report("vfio_dma_unmap(%p, 0x%"HWADDR_PRIx", "
>> +                         "0x%"HWADDR_PRIx") = %d (%m)",
>> +                         container, iotlb->iova,
>> +                         iotlb->addr_mask + 1, ret);
>> +        }
>> +    }
>> +}
>> +
>>  static void vfio_listener_region_add(MemoryListener *listener,
>>                                       MemoryRegionSection *section)
>>  {
>> @@ -2261,8 +2325,6 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>      void *vaddr;
>>      int ret;
>>  
>> -    assert(!memory_region_is_iommu(section->mr));
>> -
>>      if (vfio_listener_skipped_section(section)) {
>>          DPRINTF("SKIPPING region_add %"HWADDR_PRIx" - %"PRIx64"\n",
>>                  section->offset_within_address_space,
>> @@ -2286,15 +2348,47 @@ static void vfio_listener_region_add(MemoryListener *listener,
>>          return;
>>      }
>>  
>> +    memory_region_ref(section->mr);
>> +
>> +    if (memory_region_is_iommu(section->mr)) {
>> +        VFIOGuestIOMMU *giommu;
>> +
>> +        DPRINTF("region_add [iommu] %"HWADDR_PRIx" - %"HWADDR_PRIx"\n",
>> +                iova, int128_get64(int128_sub(llend, int128_one())));
>> +        /*
>> +         * FIXME: We should do some checking to see if the
>> +         * capabilities of the host VFIO IOMMU are adequate to model
>> +         * the guest IOMMU
>> +         *
>> +         * FIXME: This assumes that the guest IOMMU is empty of
>> +         * mappings at this point - we should either enforce this, or
>> +         * loop through existing mappings to map them into VFIO.
>> +         *
>> +         * FIXME: For VFIO iommu types which have KVM acceleration to
>> +         * avoid bouncing all map/unmaps through qemu this way, this
>> +         * would be the right place to wire that up (tell the KVM
>> +         * device emulation the VFIO iommu handles to use).
>> +         */
> 
> That's a lot of FIXMEs...  The second one in particular looks like it
> needs to expand a bit on why this is likely a valid assumption.  The
> last one is more of a TODO than a FIXME.
> 
>> +        giommu = g_malloc0(sizeof(*giommu));
>> +        giommu->iommu = section->mr;
>> +        giommu->container = container;
>> +        giommu->n.notify = vfio_iommu_map_notify;
>> +        QLIST_INSERT_HEAD(&container->giommu_list, giommu, giommu_next);
>> +        memory_region_register_iommu_notifier(giommu->iommu, &giommu->n);
>> +
>> +        return;
>> +    }
>> +
>> +    /* Here we assume that memory_region_is_ram(section->mr)==true */
>> +
>>      end = int128_get64(llend);
>>      vaddr = memory_region_get_ram_ptr(section->mr) +
>>              section->offset_within_region +
>>              (iova - section->offset_within_address_space);
>>  
>> -    DPRINTF("region_add %"HWADDR_PRIx" - %"HWADDR_PRIx" [%p]\n",
>> +    DPRINTF("region_add [ram] %"HWADDR_PRIx" - %"HWADDR_PRIx" [%p]\n",
>>              iova, end - 1, vaddr);
>>  
>> -    memory_region_ref(section->mr);
>>      ret = vfio_dma_map(container, iova, end - iova, vaddr, section->readonly);
>>      if (ret) {
>>          error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
>> @@ -2338,6 +2432,26 @@ static void vfio_listener_region_del(MemoryListener *listener,
>>          return;
>>      }
>>  
>> +    if (memory_region_is_iommu(section->mr)) {
>> +        VFIOGuestIOMMU *giommu;
>> +
>> +        QLIST_FOREACH(giommu, &container->giommu_list, giommu_next) {
>> +            if (giommu->iommu == section->mr) {
>> +                memory_region_unregister_iommu_notifier(&giommu->n);
>> +                QLIST_REMOVE(giommu, giommu_next);
>> +                g_free(giommu);
>> +                break;
>> +            }
>> +        }
>> +
>> +        /*
>> +         * FIXME: We assume the one big unmap below is adequate to
>> +         * remove any individual page mappings in the IOMMU which
>> +         * might have been copied into VFIO.  That may not be true for
>> +         * all IOMMU types
>> +         */
> 
> We assume this because the IOVA that gets unmapped is the same
> regardless of whether a guest IOMMU is present?


What exactly is meant by "guest IOMMU is present"? Doing the second DMA
window, now I am really confused about terminology :(



>> +    }
>> +
>>      iova = TARGET_PAGE_ALIGN(section->offset_within_address_space);
>>      end = (section->offset_within_address_space + int128_get64(section->size)) &
>>            TARGET_PAGE_MASK;
> 
> 
> 


-- 
Alexey