[dpdk-dev] [PATCH v3 1/1] vfio: modify spapr iommu support to use static window sizing
David Christensen
drc at linux.vnet.ibm.com
Wed Oct 7 19:44:39 CEST 2020
On 9/17/20 4:13 AM, Burakov, Anatoly wrote:
> On 10-Aug-20 10:07 PM, David Christensen wrote:
>> The SPAPR IOMMU requires that a DMA window size be defined before memory
>> can be mapped for DMA. Current code dynamically modifies the DMA window
>> size in response to every new memory allocation which is potentially
>> dangerous because all existing mappings need to be unmapped/remapped in
>> order to resize the DMA window, leaving hardware holding IOVA addresses
>> that are temporarily unmapped. The new SPAPR code statically assigns
>> the DMA window size on first use, using the largest physical memory
>> memory address when IOVA=PA and the highest existing memseg virtual
>> address when IOVA=VA.
>>
>> Signed-off-by: David Christensen <drc at linux.vnet.ibm.com>
>> ---
>
> <snip>
>
>> +struct spapr_size_walk_param {
>> + uint64_t max_va;
>> + uint64_t page_sz;
>> + int external;
>> +};
>> +
>> +/*
>> + * In order to set the DMA window size required for the SPAPR IOMMU
>> + * we need to walk the existing virtual memory allocations as well as
>> + * find the hugepage size used.
>> + */
>> static int
>> -vfio_spapr_unmap_walk(const struct rte_memseg_list *msl,
>> - const struct rte_memseg *ms, void *arg)
>> +vfio_spapr_size_walk(const struct rte_memseg_list *msl, void *arg)
>> {
>> - int *vfio_container_fd = arg;
>> + struct spapr_size_walk_param *param = arg;
>> + uint64_t max = (uint64_t) msl->base_va + (uint64_t) msl->len;
>> - /* skip external memory that isn't a heap */
>> - if (msl->external && !msl->heap)
>> - return 0;
>> + if (msl->external) {
>> + param->external++;
>> + if (!msl->heap)
>> + return 0;
>> + }
>
> It would be nice to have some comments in the code explaining what we're
> skipping and why.
Reviewing this again, my inclination is to skip ALL external memory,
which by definition would seem to be outside of IOMMU control, so the
code would read:
if (msl->external) {
param->external++;
return 0;
}
Not sure why existing code such as vfio_spapr_map_walk() distinguishes
between heap and non-heap in this situation. Are there instances in x86
where it would matter?
> Also, seems that you're using param->external as bool? This is a
> non-public API so using stdbool is not an issue here, perhaps replace it
> with bool param->has_external?
Why do you think the distinction is necessary?
Dave
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