On 24/01/2017 17:29, Alex Williamson wrote:
> On Tue, 24 Jan 2017 18:25:55 +0800
> Peter Xu <pet...@redhat.com> wrote:
>
>> A cleanup for vfio_iommu_map_notify(). Should have no functional change,
>> just to make the function shorter and easier to understand.
>>
>> Signed-off-by: Peter Xu <pet...@redhat.com>
>> ---
>> hw/vfio/common.c | 58
>> +++++++++++++++++++++++++++++++++++++-------------------
>> 1 file changed, 38 insertions(+), 20 deletions(-)
>>
>> diff --git a/hw/vfio/common.c b/hw/vfio/common.c
>> index 174f351..ce55dff 100644
>> --- a/hw/vfio/common.c
>> +++ b/hw/vfio/common.c
>> @@ -294,25 +294,14 @@ static bool
>> vfio_listener_skipped_section(MemoryRegionSection *section)
>> section->offset_within_address_space & (1ULL << 63);
>> }
>>
>> -static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>> +static bool vfio_get_vaddr(IOMMUTLBEntry *iotlb, void **vaddr,
>> + bool *read_only)
>> {
>> - VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
>> - VFIOContainer *container = giommu->container;
>> - hwaddr iova = iotlb->iova + giommu->iommu_offset;
>> MemoryRegion *mr;
>> hwaddr xlat;
>> hwaddr len = iotlb->addr_mask + 1;
>> - void *vaddr;
>> - int ret;
>> -
>> - trace_vfio_iommu_map_notify(iotlb->perm == IOMMU_NONE ? "UNMAP" : "MAP",
>> - iova, iova + iotlb->addr_mask);
>> -
>> - if (iotlb->target_as != &address_space_memory) {
>> - error_report("Wrong target AS \"%s\", only system memory is
>> allowed",
>> - iotlb->target_as->name ? iotlb->target_as->name :
>> "none");
>> - return;
>> - }
>> + bool ret = false;
>> + bool writable = iotlb->perm & IOMMU_WO;
>>
>> /*
>> * The IOMMU TLB entry we have just covers translation through
>> @@ -322,12 +311,13 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n,
>> IOMMUTLBEntry *iotlb)
>> rcu_read_lock();
>> mr = address_space_translate(&address_space_memory,
>> iotlb->translated_addr,
>> - &xlat, &len, iotlb->perm & IOMMU_WO);
>> + &xlat, &len, writable);
>> if (!memory_region_is_ram(mr)) {
>> error_report("iommu map to non memory area %"HWADDR_PRIx"",
>> xlat);
>> goto out;
>> }
>> +
>> /*
>> * Translation truncates length to the IOMMU page size,
>> * check that it did not truncate too much.
>> @@ -337,11 +327,41 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n,
>> IOMMUTLBEntry *iotlb)
>> goto out;
>> }
>>
>> + *vaddr = memory_region_get_ram_ptr(mr) + xlat;
>> + *read_only = !writable || mr->readonly;
>> + ret = true;
>> +
>> +out:
>> + rcu_read_unlock();
>> + return ret;
>> +}
>> +
>> +static void vfio_iommu_map_notify(IOMMUNotifier *n, IOMMUTLBEntry *iotlb)
>> +{
>> + VFIOGuestIOMMU *giommu = container_of(n, VFIOGuestIOMMU, n);
>> + VFIOContainer *container = giommu->container;
>> + hwaddr iova = iotlb->iova + giommu->iommu_offset;
>> + bool read_only;
>> + void *vaddr;
>> + int ret;
>> +
>> + trace_vfio_iommu_map_notify(iotlb->perm == IOMMU_NONE ? "UNMAP" : "MAP",
>> + iova, iova + iotlb->addr_mask);
>> +
>> + if (iotlb->target_as != &address_space_memory) {
>> + error_report("Wrong target AS \"%s\", only system memory is
>> allowed",
>> + iotlb->target_as->name ? iotlb->target_as->name :
>> "none");
>> + return;
>> + }
>> +
>> + if (!vfio_get_vaddr(iotlb, &vaddr, &read_only)) {
>> + return;
>> + }
>> +
>> if ((iotlb->perm & IOMMU_RW) != IOMMU_NONE) {
>> - vaddr = memory_region_get_ram_ptr(mr) + xlat;
>> ret = vfio_dma_map(container, iova,
>> iotlb->addr_mask + 1, vaddr,
>> - !(iotlb->perm & IOMMU_WO) || mr->readonly);
>> + read_only);
>> if (ret) {
>> error_report("vfio_dma_map(%p, 0x%"HWADDR_PRIx", "
>> "0x%"HWADDR_PRIx", %p) = %d (%m)",
>> @@ -357,8 +377,6 @@ static void vfio_iommu_map_notify(IOMMUNotifier *n,
>> IOMMUTLBEntry *iotlb)
>> iotlb->addr_mask + 1, ret);
>> }
>> }
>> -out:
>> - rcu_read_unlock();
>
> The comment from v4 still needs input from Paolo, is it valid to make
> use of vaddr (based on address_space_translate ->
> memory_region_get_ram_ptr) outside of the rcu read lock or could future
> BQL reduction efforts allow this to race?
You need to keep a reference to the MemoryRegion if you do
rcu_read_unlock. But it's simpler to call vfio_get_vaddr within
rcu_read_lock, and keep the lock/unlock in vfio_iommu_map_notify.
You probably should also put a comment about why VFIO does *not* need to
keep a reference between vfio_dma_map and vfio_dma_unmap (which doesn't
sound easy to do either). Would any well-behaved guest invalidate the
IOMMU page tables before a memory hot-unplug?
Paolo
>> }
>>
>> static void vfio_listener_region_add(MemoryListener *listener,
>
>
>
