From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DA6119068E; Tue, 10 Sep 2024 10:32:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725964320; cv=none; b=FrPgyF920s20GyBs0fd686d92Ezoj77TLd4n7PgYm31Gf2o3UmaFg3VlqFSERVkOC39yooWJQwZLpWVGO1nkmzrQoDNEZjkX6TLd/xsAkoUhtutb61rlTTRTN+d4UxJut1rN0XP6P0OnXs0o28mQ8hvcFvIUk1cyIyMCN01RUw4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725964320; c=relaxed/simple; bh=mFFshYL3NTitb6Ej9eISvbAzfD+a9z2QfdgKHMpMu64=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DH7vsuS9QSQS3TE9kg74I2JnnAUTip14pthlcgFegokl6ECOjprL4JHtKuC/l4ez/kdVZEs434XKfbEFc/ie1GVR8buw2oyUJkopwzHa7xy6+XkOsJfWGpmrqlKVWtk/Cz/SE9S/753qAEfYjwAGLGnDmWDh1TxZDhtDGEvjskk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zwv6yRc0; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="zwv6yRc0" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 06A3CC4CEC3; Tue, 10 Sep 2024 10:31:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1725964320; bh=mFFshYL3NTitb6Ej9eISvbAzfD+a9z2QfdgKHMpMu64=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=zwv6yRc0/0gXf+Dm2FOP2ClTu0VtNxxwltvlcya5tPwdkh+eFzqSkE25pHRRk09XW Ia+Sh5/9YPAAp8rophKFBDd46h5gzqwgGUZFY41KZiYMKacs7VEqL+6i+xPFh2cdAr S3GRJ9EIOuFIgaV8bNOYg4ANXDTgmFk+FJndIhkc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Jacob Pan , Kevin Tian , Yi Liu , Lu Baolu , Will Deacon , Sasha Levin Subject: [PATCH 6.6 142/269] iommu/vt-d: Handle volatile descriptor status read Date: Tue, 10 Sep 2024 11:32:09 +0200 Message-ID: <20240910092613.268656017@linuxfoundation.org> X-Mailer: git-send-email 2.46.0 In-Reply-To: <20240910092608.225137854@linuxfoundation.org> References: <20240910092608.225137854@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jacob Pan [ Upstream commit b5e86a95541cea737394a1da967df4cd4d8f7182 ] Queued invalidation wait descriptor status is volatile in that IOMMU hardware writes the data upon completion. Use READ_ONCE() to prevent compiler optimizations which ensures memory reads every time. As a side effect, READ_ONCE() also enforces strict types and may add an extra instruction. But it should not have negative performance impact since we use cpu_relax anyway and the extra time(by adding an instruction) may allow IOMMU HW request cacheline ownership easier. e.g. gcc 12.3 BEFORE: 81 38 ad de 00 00 cmpl $0x2,(%rax) AFTER (with READ_ONCE()) 772f: 8b 00 mov (%rax),%eax 7731: 3d ad de 00 00 cmp $0x2,%eax //status data is 32 bit Signed-off-by: Jacob Pan Reviewed-by: Kevin Tian Reviewed-by: Yi Liu Link: https://lore.kernel.org/r/20240607173817.3914600-1-jacob.jun.pan@linux.intel.com Signed-off-by: Lu Baolu Link: https://lore.kernel.org/r/20240702130839.108139-2-baolu.lu@linux.intel.com Signed-off-by: Will Deacon Signed-off-by: Sasha Levin --- drivers/iommu/intel/dmar.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c index 23cb80d62a9a..84f0459e503c 100644 --- a/drivers/iommu/intel/dmar.c +++ b/drivers/iommu/intel/dmar.c @@ -1422,7 +1422,7 @@ int qi_submit_sync(struct intel_iommu *iommu, struct qi_desc *desc, */ writel(qi->free_head << shift, iommu->reg + DMAR_IQT_REG); - while (qi->desc_status[wait_index] != QI_DONE) { + while (READ_ONCE(qi->desc_status[wait_index]) != QI_DONE) { /* * We will leave the interrupts disabled, to prevent interrupt * context to queue another cmd while a cmd is already submitted -- 2.43.0