On 29/11/17 16:32, Alex Williamson wrote:
On Thu, 23 Nov 2017 15:13:37 +1100 Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:On 17/11/17 17:58, Alexey Kardashevskiy wrote:On 17/11/17 11:13, Alex Williamson wrote:On Tue, 14 Nov 2017 10:47:12 +1100 Alexey Kardashevskiy <aik@xxxxxxxxx> wrote:On 27/10/17 14:00, Alexey Kardashevskiy wrote:This adds trace_map/trace_unmap tracepoints to spapr driver. Type1 already uses these via the IOMMU API (iommu_map/__iommu_unmap). Signed-off-by: Alexey Kardashevskiy <aik@xxxxxxxxx>Is this really legitimate to include tracepoints from a different subsystem?> The vfio type1 backend gets these trace points by virtue of it actually using the IOMMU API, it doesn't call them itself. I'm kind of surprised these are actually available to be called from a module.They are explicitly exported: EXPORT_TRACEPOINT_SYMBOL_GPL(map); EXPORT_TRACEPOINT_SYMBOL_GPL(unmap); I would think this is for things like drivers/vfio/vfio_iommu_spapr_tce.c , why else?...I suspect the way to do this is probably to define our own tracepoints in the vfio/spapr backend or insert tracepoints into the IOMMU layers that that code calls into rather than masquerading as tracepoints from a different subsystem. Right?This makes sense too. But it is going to be just cut-n-paste and some confusion - /sys/kernel/debug/tracing/events/iommu/map will still be present but won't work and /sys/kernel/debug/tracing/events/vfio/vfio_iommu_spapr_tce/map will.But iommu/map does work, it's just not called by the vfio spapr tce backend, which is absolutely correct. In fact, that's part of my reservation about this approach is that it could be interpreted as implying a call path that doesn't exist on this arch.
Come to think of it, the inverse also applies - if users are led to expect x86-like behaviour where the iommu/map tracepoint just happens to reflect VFIO calls, they'll likely also get a nasty surprise on platforms like arm64 where regular DMA API calls by drivers may be hammering iommu_map() in the background.
Robin.
Judges? :)Still nak? I discussed this locally, the conclusion was it is a matter of taste and this proposal is not that disgusting. Thanks.Is that our goal now, proposals that aren't too disgusting? I think it's an opportunity to introduce our own tracing infrastructure and it feels a lot more correct to do that than to generalize existing trace points from other subsystems. Thanks, Alex--- Example: qemu-system-ppc-8655 [096] 724.662740: unmap: IOMMU: iova=0x000000003ffff000 size=4096 unmapped_size=4096 qemu-system-ppc-8656 [104] 724.970912: map: IOMMU: iova=0x0800000000000000 paddr=0x00007ffef7ff0000 size=65536 --- drivers/vfio/vfio_iommu_spapr_tce.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c index 63112c36ab2d..4531486c77c6 100644 --- a/drivers/vfio/vfio_iommu_spapr_tce.c +++ b/drivers/vfio/vfio_iommu_spapr_tce.c @@ -22,6 +22,7 @@ #include <linux/vmalloc.h> #include <linux/sched/mm.h> #include <linux/sched/signal.h> +#include <trace/events/iommu.h>#include <asm/iommu.h>#include <asm/tce.h> @@ -502,17 +503,19 @@ static int tce_iommu_clear(struct tce_container *container, struct iommu_table *tbl, unsigned long entry, unsigned long pages) { - unsigned long oldhpa; + unsigned long oldhpa, unmapped, firstentry = entry, totalpages = pages; long ret; enum dma_data_direction direction;- for ( ; pages; --pages, ++entry) {+ for (unmapped = 0; pages; --pages, ++entry) { direction = DMA_NONE; oldhpa = 0; ret = iommu_tce_xchg(tbl, entry, &oldhpa, &direction); if (ret) continue;+ ++unmapped;+ if (direction == DMA_NONE) continue;@@ -523,6 +526,9 @@ static int tce_iommu_clear(struct tce_container *container, tce_iommu_unuse_page(container, oldhpa);} + trace_unmap(firstentry << tbl->it_page_shift, + totalpages << tbl->it_page_shift, + unmapped << tbl->it_page_shift);return 0;} @@ -965,6 +971,8 @@ static long tce_iommu_ioctl(void *iommu_data, direction);iommu_flush_tce(tbl);+ if (!ret) + trace_map(param.iova, param.vaddr, param.size);return ret;}_______________________________________________ iommu mailing list iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/iommu
