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 9D88EC5CFC1 for ; Sun, 16 Aug 2026 01:46:03 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 44CEC10E23F; Sun, 16 Aug 2026 01:46:02 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="HUC++z9+"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.10]) by gabe.freedesktop.org (Postfix) with ESMTPS id 5758510E23F; Sun, 16 Aug 2026 01:46:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1786844761; x=1818380761; h=from:to:cc:subject:date:message-id:mime-version: content-transfer-encoding; bh=It30WGELctoJSQf1hi57IpECUFR9aIkATg1Jg7hD7nw=; b=HUC++z9+C5b7G+0JykFOjs8+RsxTMpFkOxJqCt3GJGYKC6JucF+9TlzS e82huse5MrfKMSkQ++Xd/PmtwiydjPPP7qH+OiJcrCCxoDdu0oBuBanbP KOrbPVDSvghUSP/cWrJHEQwLOuo5uYQXtagkkUNt3mgGi6iYWPfcf6eBD 5j+2ZhVslPM13P6F5uameYNoYl5ahGDZOK+NOFi+qY2g7HWKrBa8CmUZ6 weW5OdyLOrkysVMsmYKRsSfMlLYgy3oBQ+3sxkgpA9TuOYodF5P816fTH YW9SA95hdAHN4RgQjy4Mu5yXdCcOyRLFMTTY9TmTpThH+qxt9maBUuiO9 w==; X-CSE-ConnectionGUID: IRkCMf+OTIO5bGDQm7i1OQ== X-CSE-MsgGUID: lUW79Mb7TWWxRTcG7Q+AJA== X-IronPort-AV: E=McAfee;i="6800,10657,11876"; a="98729442" X-IronPort-AV: E=Sophos;i="6.25,226,1779174000"; d="scan'208";a="98729442" Received: from fmviesa005.fm.intel.com ([10.60.135.145]) by fmvoesa104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Aug 2026 18:46:00 -0700 X-CSE-ConnectionGUID: Wm91vM66T9qkYSiYchjHDg== X-CSE-MsgGUID: kQauwJtHQKemrJyICo5qIA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,226,1779174000"; d="scan'208";a="269760674" Received: from clke06vm103.fm.intel.com (HELO clke06vm103.amr.corp.intel.com) ([10.80.128.218]) by fmviesa005.fm.intel.com with ESMTP; 15 Aug 2026 18:46:00 -0700 From: "Prabhakaran, Krishna" To: intel-gfx@lists.freedesktop.org Cc: jani.nikula@linux.intel.com, joonas.lahtinen@linux.intel.com, rodrigo.vivi@intel.com, tursulin@ursulin.net, matthew.auld@intel.com, thomas.hellstrom@linux.intel.com, dri-devel@lists.freedesktop.org, Krishna Prabhakaran Subject: [PATCH v2] drm/i915/dmabuf: avoid global wbinvd on dma-buf import Date: Sat, 15 Aug 2026 18:45:52 -0700 Message-ID: <20260816014552.14969-1-krishna.prabhakaran@intel.com> X-Mailer: git-send-email 2.43.0 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 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). - 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 --- v2: - Flush our own imported dma-bufs directly with drm_clflush_sg() instead of dma_buf_vmap(), which re-entered i915_gem_object_pin_map() on the source object and failed igt_dmabuf_import_same_driver_smem with -EBUSY (reported by Intel CI on v1). Foreign dma-bufs still use dma_buf_vmap() + drm_clflush_virt_range(); wbinvd only as fallback. - Link to v1: https://patchwork.freedesktop.org/patch/744955/?series=171760 drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c | 55 ++++++++++++++++++---- 1 file changed, 47 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..c798a90f1c0f 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 +251,53 @@ 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 backing + * object is struct-page backed once migrated to SMEM, + * so 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. + */ + 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); base-commit: 682ea2d28d18bb06f9fc663cb5ab7e80dc0e606a -- 2.43.0