On Wed, Nov 06, 2024 at 04:44:15PM +0100, Christian König wrote: > Am 06.11.24 um 16:25 schrieb Matthew Brost: > > [SNIP] > > > Can you fully describe your use case? In other words what exactly is your > > > debugger trying to do? > > See above; I hope I've made this clearer. > > It at least sounds a little bit better. > > > Also, I'm not really an expert on Eudebug, as I haven't been involved in > > the development aside from reviewing its interaction with the core of > > Xe. Any further explanation would likely require me to loop in a > > colleague. > > I think that could help since I don't have a clear picture of your use case. > > > > > Well, I think we need to take a step back. The major question is what is > > > your use case and is that use case valid or causes security concerns. > > > > > > For example userptrs are imported anonymous pages the GPU has a DMA mapping > > > for. Re-mapping them into an user address space for debugging or even > > > accessing them through the ptrace interface is strictly forbidden. > > > > > > We already had people trying to do exactly that and it ended not well at > > > all. > > > > > Again, if we can focus on what this patch is doing—accessing a BO, not a > > userptr—I think that will help progress here. > > > > To bring things together: "There is a huge push from upstream to avoid > > using kmap/vmap if possible." How would you suggest accessing a BO then? > > Well that's the whole point: You should *not* access the BO on behalves of > userspace in a peek/poke like interface. > This is not a generic interface that anyone can freely access. The same permissions used by ptrace are checked when opening such an interface. See [1] [2]. [1] https://patchwork.freedesktop.org/patch/617470/?series=136572&rev=2 [2] https://patchwork.freedesktop.org/patch/617471/?series=136572&rev=2 > > kmap/vmap are used everywhere in the DRM subsystem to access BOs, so I’m > > failing to see the problem with adding a simple helper based on existing > > code. > > What#s possible and often done is to do kmap/vmap if you need to implement a > CPU copy for scanout for example or for copying/validating command buffers. > But that usually requires accessing the whole BO and has separate security > checks. > > When you want to access only a few bytes of a BO that sounds massively like > a peek/poke like interface and we have already rejected that more than once. > There even used to be standardized GEM IOCTLs for that which have been > removed by now. > > If you need to access BOs which are placed in not CPU accessible memory then > implement the access callback for ptrace, see amdgpu_ttm_access_memory for > an example how to do this. > Ptrace access via vm_operations_struct.access → ttm_bo_vm_access. This series renames ttm_bo_vm_access to ttm_bo_access, with no code changes. The above function accesses a BO via kmap if it is in SYSTEM / TT, which is existing code. This function is only exposed to user space via ptrace permissions. In this series, we implement a function [3] similar to amdgpu_ttm_access_memory for the TTM vfunc access_memory. What is missing is non-visible CPU memory access, similar to amdgpu_ttm_access_memory_sdma. This will be addressed in a follow-up and was omitted in this series given its complexity. So, this looks more or less identical to AMD's ptrace implementation, but in GPU address space. Again, I fail to see what the problem is here. What am I missing? Matt [3] https://patchwork.freedesktop.org/patch/622520/?series=140200&rev=6 > Regards, > Christian. > > > > > Matt > > > > > Regards, > > > Christian. > > > > > > > With this, I strongly prefer the code as is. > > > > > > > > Matt > > > > > > > > > Regards, > > > > > Christian. > > > > > > > > > > > Matt > > > > > > > > > > > > > Regards, > > > > > > > Christian. > > > > > > > > > > > > > > > > Matt > > > > > > > > > > > > > > > > > > > Reported-by: Christoph Manszewski<christoph.manszewski@xxxxxxxxx> > > > > > > > > > > Suggested-by: Thomas Hellström<thomas.hellstrom@xxxxxxxxxxxxxxx> > > > > > > > > > > Signed-off-by: Matthew Brost<matthew.brost@xxxxxxxxx> > > > > > > > > > > Tested-by: Mika Kuoppala<mika.kuoppala@xxxxxxxxxxxxxxx> > > > > > > > > > > Reviewed-by: Matthew Auld<matthew.auld@xxxxxxxxx> > > > > > > > > > > --- > > > > > > > > > > drivers/gpu/drm/ttm/ttm_bo_util.c | 86 +++++++++++++++++++++++++++++++ > > > > > > > > > > drivers/gpu/drm/ttm/ttm_bo_vm.c | 65 +---------------------- > > > > > > > > > > include/drm/ttm/ttm_bo.h | 2 + > > > > > > > > > > 3 files changed, 89 insertions(+), 64 deletions(-) > > > > > > > > > > > > > > > > > > > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c > > > > > > > > > > index d939925efa81..77e760ea7193 100644 > > > > > > > > > > --- a/drivers/gpu/drm/ttm/ttm_bo_util.c > > > > > > > > > > +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c > > > > > > > > > > @@ -919,3 +919,89 @@ s64 ttm_lru_walk_for_evict(struct ttm_lru_walk *walk, struct ttm_device *bdev, > > > > > > > > > > return progress; > > > > > > > > > > } > > > > > > > > > > + > > > > > > > > > > +static int ttm_bo_access_kmap(struct ttm_buffer_object *bo, > > > > > > > > > > + unsigned long offset, > > > > > > > > > > + void *buf, int len, int write) > > > > > > > > > > +{ > > > > > > > > > > + unsigned long page = offset >> PAGE_SHIFT; > > > > > > > > > > + unsigned long bytes_left = len; > > > > > > > > > > + int ret; > > > > > > > > > > + > > > > > > > > > > + /* Copy a page at a time, that way no extra virtual address > > > > > > > > > > + * mapping is needed > > > > > > > > > > + */ > > > > > > > > > > + offset -= page << PAGE_SHIFT; > > > > > > > > > > + do { > > > > > > > > > > + unsigned long bytes = min(bytes_left, PAGE_SIZE - offset); > > > > > > > > > > + struct ttm_bo_kmap_obj map; > > > > > > > > > > + void *ptr; > > > > > > > > > > + bool is_iomem; > > > > > > > > > > + > > > > > > > > > > + ret = ttm_bo_kmap(bo, page, 1, &map); > > > > > > > > > > + if (ret) > > > > > > > > > > + return ret; > > > > > > > > > > + > > > > > > > > > > + ptr = (void *)ttm_kmap_obj_virtual(&map, &is_iomem) + offset; > > > > > > > > > > + WARN_ON_ONCE(is_iomem); > > > > > > > > > > + if (write) > > > > > > > > > > + memcpy(ptr, buf, bytes); > > > > > > > > > > + else > > > > > > > > > > + memcpy(buf, ptr, bytes); > > > > > > > > > > + ttm_bo_kunmap(&map); > > > > > > > > > > + > > > > > > > > > > + page++; > > > > > > > > > > + buf += bytes; > > > > > > > > > > + bytes_left -= bytes; > > > > > > > > > > + offset = 0; > > > > > > > > > > + } while (bytes_left); > > > > > > > > > > + > > > > > > > > > > + return len; > > > > > > > > > > +} > > > > > > > > > > + > > > > > > > > > > +/** > > > > > > > > > > + * ttm_bo_access - Helper to access a buffer object > > > > > > > > > > + * > > > > > > > > > > + * @bo: ttm buffer object > > > > > > > > > > + * @offset: access offset into buffer object > > > > > > > > > > + * @buf: pointer to caller memory to read into or write from > > > > > > > > > > + * @len: length of access > > > > > > > > > > + * @write: write access > > > > > > > > > > + * > > > > > > > > > > + * Utility function to access a buffer object. Useful when buffer object cannot > > > > > > > > > > + * be easily mapped (non-contiguous, non-visible, etc...). > > > > > > > > > > + * > > > > > > > > > > + * Returns: > > > > > > > > > > + * @len if successful, negative error code on failure. > > > > > > > > > > + */ > > > > > > > > > > +int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset, > > > > > > > > > > + void *buf, int len, int write) > > > > > > > > > > +{ > > > > > > > > > > + int ret; > > > > > > > > > > + > > > > > > > > > > + if (len < 1 || (offset + len) > bo->base.size) > > > > > > > > > > + return -EIO; > > > > > > > > > > + > > > > > > > > > > + ret = ttm_bo_reserve(bo, true, false, NULL); > > > > > > > > > > + if (ret) > > > > > > > > > > + return ret; > > > > > > > > > > + > > > > > > > > > > + switch (bo->resource->mem_type) { > > > > > > > > > > + case TTM_PL_SYSTEM: > > > > > > > > > > + fallthrough; > > > > > > > > > > + case TTM_PL_TT: > > > > > > > > > > + ret = ttm_bo_access_kmap(bo, offset, buf, len, write); > > > > > > > > > > + break; > > > > > > > > > > + default: > > > > > > > > > > + if (bo->bdev->funcs->access_memory) > > > > > > > > > > + ret = bo->bdev->funcs->access_memory > > > > > > > > > > + (bo, offset, buf, len, write); > > > > > > > > > > + else > > > > > > > > > > + ret = -EIO; > > > > > > > > > > + } > > > > > > > > > > + > > > > > > > > > > + ttm_bo_unreserve(bo); > > > > > > > > > > + > > > > > > > > > > + return ret; > > > > > > > > > > +} > > > > > > > > > > +EXPORT_SYMBOL(ttm_bo_access); > > > > > > > > > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c > > > > > > > > > > index 2c699ed1963a..20b1e5f78684 100644 > > > > > > > > > > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c > > > > > > > > > > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c > > > > > > > > > > @@ -366,45 +366,6 @@ void ttm_bo_vm_close(struct vm_area_struct *vma) > > > > > > > > > > } > > > > > > > > > > EXPORT_SYMBOL(ttm_bo_vm_close); > > > > > > > > > > -static int ttm_bo_vm_access_kmap(struct ttm_buffer_object *bo, > > > > > > > > > > - unsigned long offset, > > > > > > > > > > - uint8_t *buf, int len, int write) > > > > > > > > > > -{ > > > > > > > > > > - unsigned long page = offset >> PAGE_SHIFT; > > > > > > > > > > - unsigned long bytes_left = len; > > > > > > > > > > - int ret; > > > > > > > > > > - > > > > > > > > > > - /* Copy a page at a time, that way no extra virtual address > > > > > > > > > > - * mapping is needed > > > > > > > > > > - */ > > > > > > > > > > - offset -= page << PAGE_SHIFT; > > > > > > > > > > - do { > > > > > > > > > > - unsigned long bytes = min(bytes_left, PAGE_SIZE - offset); > > > > > > > > > > - struct ttm_bo_kmap_obj map; > > > > > > > > > > - void *ptr; > > > > > > > > > > - bool is_iomem; > > > > > > > > > > - > > > > > > > > > > - ret = ttm_bo_kmap(bo, page, 1, &map); > > > > > > > > > > - if (ret) > > > > > > > > > > - return ret; > > > > > > > > > > - > > > > > > > > > > - ptr = (uint8_t *)ttm_kmap_obj_virtual(&map, &is_iomem) + offset; > > > > > > > > > > - WARN_ON_ONCE(is_iomem); > > > > > > > > > > - if (write) > > > > > > > > > > - memcpy(ptr, buf, bytes); > > > > > > > > > > - else > > > > > > > > > > - memcpy(buf, ptr, bytes); > > > > > > > > > > - ttm_bo_kunmap(&map); > > > > > > > > > > - > > > > > > > > > > - page++; > > > > > > > > > > - buf += bytes; > > > > > > > > > > - bytes_left -= bytes; > > > > > > > > > > - offset = 0; > > > > > > > > > > - } while (bytes_left); > > > > > > > > > > - > > > > > > > > > > - return len; > > > > > > > > > > -} > > > > > > > > > > - > > > > > > > > > > int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr, > > > > > > > > > > void *buf, int len, int write) > > > > > > > > > > { > > > > > > > > > > @@ -412,32 +373,8 @@ int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr, > > > > > > > > > > unsigned long offset = (addr) - vma->vm_start + > > > > > > > > > > ((vma->vm_pgoff - drm_vma_node_start(&bo->base.vma_node)) > > > > > > > > > > << PAGE_SHIFT); > > > > > > > > > > - int ret; > > > > > > > > > > - > > > > > > > > > > - if (len < 1 || (offset + len) > bo->base.size) > > > > > > > > > > - return -EIO; > > > > > > > > > > - ret = ttm_bo_reserve(bo, true, false, NULL); > > > > > > > > > > - if (ret) > > > > > > > > > > - return ret; > > > > > > > > > > - > > > > > > > > > > - switch (bo->resource->mem_type) { > > > > > > > > > > - case TTM_PL_SYSTEM: > > > > > > > > > > - fallthrough; > > > > > > > > > > - case TTM_PL_TT: > > > > > > > > > > - ret = ttm_bo_vm_access_kmap(bo, offset, buf, len, write); > > > > > > > > > > - break; > > > > > > > > > > - default: > > > > > > > > > > - if (bo->bdev->funcs->access_memory) > > > > > > > > > > - ret = bo->bdev->funcs->access_memory( > > > > > > > > > > - bo, offset, buf, len, write); > > > > > > > > > > - else > > > > > > > > > > - ret = -EIO; > > > > > > > > > > - } > > > > > > > > > > - > > > > > > > > > > - ttm_bo_unreserve(bo); > > > > > > > > > > - > > > > > > > > > > - return ret; > > > > > > > > > > + return ttm_bo_access(bo, offset, buf, len, write); > > > > > > > > > > } > > > > > > > > > > EXPORT_SYMBOL(ttm_bo_vm_access); > > > > > > > > > > diff --git a/include/drm/ttm/ttm_bo.h b/include/drm/ttm/ttm_bo.h > > > > > > > > > > index 5804408815be..8ea11cd8df39 100644 > > > > > > > > > > --- a/include/drm/ttm/ttm_bo.h > > > > > > > > > > +++ b/include/drm/ttm/ttm_bo.h > > > > > > > > > > @@ -421,6 +421,8 @@ void ttm_bo_unpin(struct ttm_buffer_object *bo); > > > > > > > > > > int ttm_bo_evict_first(struct ttm_device *bdev, > > > > > > > > > > struct ttm_resource_manager *man, > > > > > > > > > > struct ttm_operation_ctx *ctx); > > > > > > > > > > +int ttm_bo_access(struct ttm_buffer_object *bo, unsigned long offset, > > > > > > > > > > + void *buf, int len, int write); > > > > > > > > > > vm_fault_t ttm_bo_vm_reserve(struct ttm_buffer_object *bo, > > > > > > > > > > struct vm_fault *vmf); > > > > > > > > > > vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf, > > > > > > > > > > -- > > > > > > > > > > 2.34.1 > > > > > > > > > >
