From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A7B2AC624D4 for ; Wed, 2 Sep 2026 19:32:07 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id CE25610E43B; Wed, 2 Sep 2026 19:32:06 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="mtK7d3w5"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.9]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3E9DF10E43B; Wed, 2 Sep 2026 19:32:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1788377525; x=1819913525; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=wz5xNFAguyQKt79gMIwIhCHy5/68ybbYq0ip6RUB71k=; b=mtK7d3w5FoBOrMf0f3BhyB3VvRzaMAY19ge5HycaXxNAJtnKBb7mONuI rM+MbHyKGCL0MT1Awpluf24gmdrBYLhZb91MTNM1JvMmW49Lot+9lCtWy JSrFTOUJ/0+XnPkmSzHBoKrCXl6OzKNHimaomqA/kYxfjDClWBTwG058k v5T3CLph4o/JuHMvKwsUJnUamWNEG42ggpHIMiSTKoO1CCSg8+STyI+K8 9B0uAK+XBHyUWCuYGtXYEfByXcto+3Y8ru7aWHp+rcEcNZGv5QzyVETuW n1r+fHzEoO7cma1Kq0vBuogajh/QWxIO/IDbixymf+RZY0MzQv1/9LYIl A==; X-CSE-ConnectionGUID: hVUAF2iAQoWTG7KyNBNxZA== X-CSE-MsgGUID: x2RROzMCRa6tHu6G9SIMUQ== X-IronPort-AV: E=McAfee;i="6800,10657,11894"; a="111622001" X-IronPort-AV: E=Sophos;i="6.25,258,1779174000"; d="scan'208";a="111622001" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by orvoesa101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Sep 2026 12:32:05 -0700 X-CSE-ConnectionGUID: En4Ike+DRoaopBA27eHvBA== X-CSE-MsgGUID: c6c8eZSuScGj1wTDSurGqQ== X-ExtLoop1: 1 Received: from clke06vm103.fm.intel.com (HELO clke06vm103.amr.corp.intel.com) ([10.80.128.218]) by fmviesa003.fm.intel.com with ESMTP; 02 Sep 2026 12:32:04 -0700 From: "Prabhakaran, Krishna" To: intel-gfx@lists.freedesktop.org Cc: dri-devel@lists.freedesktop.org, Matthew Auld , =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Krishna Prabhakaran Subject: [PATCH v4] drm/i915/dmabuf: avoid global wbinvd on dma-buf import Date: Wed, 2 Sep 2026 12:31:47 -0700 Message-ID: <20260902193147.3835028-1-krishna.prabhakaran@intel.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260820205031.344338-1-krishna.prabhakaran@intel.com> References: <20260820205031.344338-1-krishna.prabhakaran@intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" From: Krishna Prabhakaran When i915 needs to make an imported dma-buf coherent for GPU access on non-LLC platforms, or for objects that bypass LLC, it currently calls wbinvd_on_all_cpus(). get_pages() runs whenever an imported buffer is pinned, so this triggers a whole-cache write-back and invalidate, broadcast by IPI to every CPU, on every execbuf submission involving an imported dma-buf. That stalls the entire machine for milliseconds and starves latency-sensitive work on unrelated cores (e.g. USB isochronous audio serviced on the VMM's main thread). Flush only the pages that actually need it instead: - If we imported one of our own dma-bufs, the backing object is normally struct-page backed once migrated to SMEM, so flush it directly with drm_clflush_sg(), exactly as we flush our other objects. This also avoids re-entering the exporter through dma_buf_vmap(), which would recurse into i915_gem_object_pin_map() on the source object we already hold locked (and fails the igt_dmabuf_import_same_driver selftest with -EBUSY). SMEM does not guarantee the struct-page flag though: phys objects clear it and it is dropped transiently during TTM moves, and drm_clflush_sg() walks the sgt with sg_page(), so guard the direct flush with i915_gem_object_has_struct_page() and fall back to wbinvd when it is not set. - For a foreign dma-buf the sg_table is not guaranteed to be backed by struct pages, and the importer has no way to tell, so drm_clflush_sg() cannot be used. vmap the buffer and flush that virtual range with drm_clflush_virt_range() instead: x86 uses PIPT caches, so flushing one virtual alias evicts the cache lines for every alias of the same physical pages. The dma_resv lock required by dma_buf_vmap() is already held here via the imported object. Fall back to wbinvd only when the buffer cannot be vmapped or is backed by I/O memory, where there is no CPU-side range to clflush. Fixes: a035154da45d ("drm/i915/dmabuf: add paranoid flush-on-acquire") Signed-off-by: Krishna Prabhakaran --- v4: Guard the own-dma-buf direct drm_clflush_sg() with i915_gem_object_has_struct_page() and fall back to wbinvd when the SMEM object is not struct-page backed (phys objects, transient TTM moves); sg_page() would otherwise walk bogus pages. (review feedback) v3: Drop the wbinvd fallback inside the own-dma-buf branch; the exporter is migrated to SMEM on attach, so flushing device memory made no sense. (Matthew Auld) v2: Special-case our own dma-bufs with drm_clflush_sg() instead of dma_buf_vmap(), which recursed into i915_gem_object_pin_map() on the already-locked source object and failed igt_dmabuf_import_same_driver with -EBUSY; foreign dma-bufs use vmap + drm_clflush_virt_range(). v1: https://patchwork.freedesktop.org/series/171760/ drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 62 +++++++++++++++++++--- 1 file changed, 54 insertions(+), 8 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c index b43d34c7d641..d1695171019c 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c @@ -10,6 +10,8 @@ #include +#include + #include "gem/i915_gem_dmabuf.h" #include "i915_drv.h" #include "i915_gem_object.h" @@ -249,16 +251,60 @@ static int i915_gem_object_get_pages_dmabuf(struct drm_i915_gem_object *obj) * DG1 is special here since it still snoops transactions even with * CACHE_NONE. This is not the case with other HAS_SNOOP platforms. We * might need to revisit this as we add new discrete platforms. - * - * XXX: Consider doing a vmap flush or something, where possible. - * Currently we just do a heavy handed wbinvd_on_all_cpus() here since - * the underlying sg_table might not even point to struct pages, so we - * can't just call drm_clflush_sg or similar, like we do elsewhere in - * the driver. */ if (i915_gem_object_can_bypass_llc(obj) || - (!HAS_LLC(i915) && !IS_DG1(i915))) - wbinvd_on_all_cpus(); + (!HAS_LLC(i915) && !IS_DG1(i915))) { + struct dma_buf *dma_buf = obj->base.import_attach->dmabuf; + + if (dma_buf->ops == &i915_dmabuf_ops) { + struct drm_i915_gem_object *dma_obj = + dma_buf_to_obj(dma_buf); + + /* + * We imported one of our own dma-bufs. The exporter is + * migrated to SMEM on attach, so it is normally struct-page + * backed and we can flush it directly, the same way we + * flush our other objects. This also avoids re-entering + * the exporter through dma_buf_vmap(), which would + * recurse into i915_gem_object_pin_map() on the source + * object we already hold locked. + * + * SMEM does not guarantee the STRUCT_PAGE flag though: phys + * objects clear it and it is dropped transiently during TTM + * moves. drm_clflush_sg() walks the sgt with sg_page(), so + * without struct pages those pointers are bogus; fall back to + * wbinvd in that case (not the vmap path, which would recurse + * on the already-locked source object). + */ + if (i915_gem_object_has_struct_page(dma_obj)) + drm_clflush_sg(dma_obj->mm.pages); + else + wbinvd_on_all_cpus(); + } else { + struct iosys_map map; + + /* + * A foreign sg_table is not guaranteed to be backed by + * struct pages, so we cannot use drm_clflush_sg(). vmap + * the buffer and flush the virtual range instead; x86 + * uses PIPT caches, so flushing one alias evicts the + * lines for every alias of the same physical pages. + * + * We already hold the dma_resv lock via the imported + * obj, so use the locked dma_buf_vmap() variant. + */ + if (!dma_buf_vmap(dma_buf, &map)) { + if (!map.is_iomem) + drm_clflush_virt_range(map.vaddr, + obj->base.size); + else + wbinvd_on_all_cpus(); + dma_buf_vunmap(dma_buf, &map); + } else { + wbinvd_on_all_cpus(); + } + } + } __i915_gem_object_set_pages(obj, sgt); -- 2.43.0