[PATCH 1/2] drm/xe/lnl: Only do gpu sys page clear for non-pooled BOs
Nirmoy Das
nirmoy.das at linux.intel.com
Wed Aug 28 09:08:19 UTC 2024
Hi Thomas,
On 8/28/2024 10:09 AM, Thomas Hellström wrote:
> On Wed, 2024-08-21 at 11:50 +0200, Nirmoy Das wrote:
>> Currently XE lacks clean-on-free implementation so using
>> TTM_TT_FLAG_CLEARED_ON_FREE is invalid. Remove usage of
>> TTM_TT_FLAG_CLEARED_ON_FREE and limit gpu system page clearing
>> only for WB cached BOs which are not pooled so there is no need to
>> return a zeroed pages to a pool.
>>
>> Without the patch:
>> api_overhead_benchmark_l0 --testFilter=UsmMemoryAllocation:
>> UsmMemoryAllocation(api=l0 type=Host size=4KB) 79.439 us
>> UsmMemoryAllocation(api=l0 type=Host size=1GB) 98677.75 us
>> Perf tool top 5 entries:
>> 11.16% api_overhead_be [kernel.kallsyms] [k] __pageblock_pfn_to_page
>> 7.85% api_overhead_be [kernel.kallsyms] [k] cpa_flush
>> 7.59% api_overhead_be [kernel.kallsyms] [k] find_next_iomem_res
>> 7.24% api_overhead_be [kernel.kallsyms] [k] pages_are_mergeable
>> 5.53% api_overhead_be [kernel.kallsyms] [k]
>> lookup_address_in_pgd_attr
>>
>> With the patch:
>> UsmMemoryAllocation(api=l0 type=Host size=4KB) 78.164 us
>> UsmMemoryAllocation(api=l0 type=Host size=1GB) 98880.39 us
>> Perf tool top 5 entries:
>> 25.40% api_overhead_be [kernel.kallsyms] [k] clear_page_erms
>> 9.89% api_overhead_be [kernel.kallsyms] [k] pages_are_mergeable
>> 4.64% api_overhead_be [kernel.kallsyms] [k] cpa_flush
>> 4.04% api_overhead_be [kernel.kallsyms] [k] find_next_iomem_res
>> 3.96% api_overhead_be [kernel.kallsyms] [k] mod_find
>>
>> This is still better than the base case where there was no
>> page clearing offloading.
>>
>> Cc: Christian König <christian.koenig at amd.com>
>> Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray at intel.com>
>> Cc: Matthew Auld <matthew.auld at intel.com>
>> Cc: Matthew Brost <matthew.brost at intel.com>
>> Cc: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>> Signed-off-by: Nirmoy Das <nirmoy.das at intel.com>
> Nirmoy, is it possible to split this up into a revert and then added
> functionality so that we could quickly revert the security issue end
> then add a separate patch that is an optimization?
Sent out a new series to clean revert both patches so it could be merge
soon.
Regards,
Nirmoy
>
> /Thomas
>
>> ---
>> drivers/gpu/drm/xe/xe_bo.c | 27 +++++++++++++++++++--------
>> 1 file changed, 19 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index 6ed0e1955215..a18408d5d185 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -283,6 +283,7 @@ struct xe_ttm_tt {
>> struct device *dev;
>> struct sg_table sgt;
>> struct sg_table *sg;
>> + bool clear_system_pages;
>> };
>>
>> static int xe_tt_map_sg(struct ttm_tt *tt)
>> @@ -397,12 +398,17 @@ static struct ttm_tt *xe_ttm_tt_create(struct
>> ttm_buffer_object *ttm_bo,
>> }
>>
>> /*
>> - * If the device can support gpu clear system pages then set
>> proper ttm
>> + * If the device can support gpu clear system pages then set
>> proper
>> * flag. Zeroed pages are only required for
>> ttm_bo_type_device so
>> * unwanted data is not leaked to userspace.
>> + *
>> + * XE currently does clear-on-alloc so gpu clear will only
>> work on
>> + * non-pooled BO, DRM_XE_GEM_CPU_CACHING_WB otherwise global
>> pool will
>> + * get poisoned ono-zeroed pages.
>> */
>> - if (ttm_bo->type == ttm_bo_type_device && xe-
>>> mem.gpu_page_clear_sys)
>> - page_flags |= TTM_TT_FLAG_CLEARED_ON_FREE;
>> + if (ttm_bo->type == ttm_bo_type_device && xe-
>>> mem.gpu_page_clear_sys &&
>> + bo->cpu_caching == DRM_XE_GEM_CPU_CACHING_WB)
>> + tt->clear_system_pages = true;
>>
>> err = ttm_tt_init(&tt->ttm, &bo->ttm, page_flags, caching,
>> extra_pages);
>> if (err) {
>> @@ -416,8 +422,11 @@ static struct ttm_tt *xe_ttm_tt_create(struct
>> ttm_buffer_object *ttm_bo,
>> static int xe_ttm_tt_populate(struct ttm_device *ttm_dev, struct
>> ttm_tt *tt,
>> struct ttm_operation_ctx *ctx)
>> {
>> + struct xe_ttm_tt *xe_tt;
>> int err;
>>
>> + xe_tt = container_of(tt, struct xe_ttm_tt, ttm);
>> +
>> /*
>> * dma-bufs are not populated with pages, and the dma-
>> * addresses are set up when moved to XE_PL_TT.
>> @@ -426,7 +435,7 @@ static int xe_ttm_tt_populate(struct ttm_device
>> *ttm_dev, struct ttm_tt *tt,
>> return 0;
>>
>> /* Clear TTM_TT_FLAG_ZERO_ALLOC when GPU is set to clear
>> system pages */
>> - if (tt->page_flags & TTM_TT_FLAG_CLEARED_ON_FREE)
>> + if (xe_tt->clear_system_pages)
>> tt->page_flags &= ~TTM_TT_FLAG_ZERO_ALLOC;
>>
>> err = ttm_pool_alloc(&ttm_dev->pool, tt, ctx);
>> @@ -664,6 +673,7 @@ static int xe_bo_move(struct ttm_buffer_object
>> *ttm_bo, bool evict,
>> struct ttm_resource *old_mem = ttm_bo->resource;
>> u32 old_mem_type = old_mem ? old_mem->mem_type :
>> XE_PL_SYSTEM;
>> struct ttm_tt *ttm = ttm_bo->ttm;
>> + struct xe_ttm_tt *xe_tt = container_of(ttm, struct
>> xe_ttm_tt, ttm);
>> struct xe_migrate *migrate = NULL;
>> struct dma_fence *fence;
>> bool move_lacks_source;
>> @@ -671,15 +681,16 @@ static int xe_bo_move(struct ttm_buffer_object
>> *ttm_bo, bool evict,
>> bool needs_clear;
>> bool handle_system_ccs = (!IS_DGFX(xe) &&
>> xe_bo_needs_ccs_pages(bo) &&
>> ttm && ttm_tt_is_populated(ttm)) ?
>> true : false;
>> - bool clear_system_pages;
>> + bool clear_system_pages = false;
>> int ret = 0;
>>
>> /*
>> * Clear TTM_TT_FLAG_CLEARED_ON_FREE on bo creation path
>> when
>> * moving to system as the bo doesn't have dma_mapping.
>> */
>> - if (!old_mem && ttm && !ttm_tt_is_populated(ttm))
>> - ttm->page_flags &= ~TTM_TT_FLAG_CLEARED_ON_FREE;
>> + if (!old_mem && ttm && !ttm_tt_is_populated(ttm) &&
>> + xe_tt->clear_system_pages)
>> + xe_tt->clear_system_pages = false;
>>
>> /* Bo creation path, moving to system or TT. */
>> if ((!old_mem && ttm) && !handle_system_ccs) {
>> @@ -703,7 +714,7 @@ static int xe_bo_move(struct ttm_buffer_object
>> *ttm_bo, bool evict,
>> move_lacks_source = handle_system_ccs ? (!bo->ccs_cleared)
>> :
>> (!mem_type_is_vram(o
>> ld_mem_type) && !tt_has_data);
>>
>> - clear_system_pages = ttm && (ttm->page_flags &
>> TTM_TT_FLAG_CLEARED_ON_FREE);
>> + clear_system_pages = ttm && xe_tt->clear_system_pages;
>> needs_clear = (ttm && ttm->page_flags &
>> TTM_TT_FLAG_ZERO_ALLOC) ||
>> (!ttm && ttm_bo->type == ttm_bo_type_device) ||
>> clear_system_pages;
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