From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (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 A8E39225D2 for ; Tue, 13 Feb 2024 09:31:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707816719; cv=none; b=fwatX0Rvttt4Wihy8EgTv1itwyCNZzKUT6pXsLrxWvLO4iQkvRt7VkpX1R6DYFXGTjsNQl+aWBmW1C6Sfoy1FrrAOWLuP6z9Gj+Go/vFz+SfKeSMZ+wJNdnvnBU0KDFnUBfZg1DZh4JNf9F3m8FB3lfqsY+YMu43Y21DIAzQz7U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707816719; c=relaxed/simple; bh=VkFFewy5/FvdeMZkM5YfhsBOBTOZwYA4mq3NdZARql4=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=rGDHnj8LHKVUPVHv91+C4BNMODo5SR12Gi2S5LL+kWlOALSRB6+k24LdjTXfqu6bdBglrzXKSrH8X77dsw8+k8GHPRjI2iybzza+FeYe0n7j0xTsRb8V0EZxsKkRUaNCmpN+Eh7M2uyZB/sD7pggReODcvxicJdxH4sseip22Sw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=Huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=Huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.18.186.31]) by frasgout.his.huawei.com (SkyGuard) with ESMTP id 4TYwww2TkPz6F97k; Tue, 13 Feb 2024 17:28:16 +0800 (CST) Received: from lhrpeml500005.china.huawei.com (unknown [7.191.163.240]) by mail.maildlp.com (Postfix) with ESMTPS id BEA021413D4; Tue, 13 Feb 2024 17:31:53 +0800 (CST) Received: from localhost (10.202.227.76) by lhrpeml500005.china.huawei.com (7.191.163.240) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.35; Tue, 13 Feb 2024 09:31:53 +0000 Date: Tue, 13 Feb 2024 09:31:52 +0000 From: Jonathan Cameron To: fan CC: , , , , , , , , , "Fan Ni" Subject: Re: [PATCH v3 9/9] hw/mem/cxl_type3: Add dpa range validation for accesses to dc regions Message-ID: <20240213093152.000017d5@Huawei.com> In-Reply-To: References: <20231107180907.553451-1-nifan.cxl@gmail.com> <20231107180907.553451-10-nifan.cxl@gmail.com> <20240124165815.00007e46@Huawei.com> Organization: Huawei Technologies Research and Development (UK) Ltd. X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml100001.china.huawei.com (7.191.160.183) To lhrpeml500005.china.huawei.com (7.191.163.240) > > > diff --git a/hw/mem/cxl_type3.c b/hw/mem/cxl_type3.c > > > index 43cea3d818..4ec65a751a 100644 > > > --- a/hw/mem/cxl_type3.c > > > +++ b/hw/mem/cxl_type3.c > > > > > +/* > > > + * Check whether a DPA range [dpa, dpa + len) has been backed with DC extents. > > > + * Used when validating read/write to dc regions > > > + */ > > > +bool ct3_test_region_block_backed(CXLType3Dev *ct3d, uint64_t dpa, > > > + uint64_t len) > > > +{ > > > + CXLDCDRegion *region; > > > + uint64_t nbits; > > > + long nr; > > > + > > > + region = cxl_find_dc_region(ct3d, dpa, len); > > > + if (!region) { > > > + return false; > > > + } > > > + > > > + nr = (dpa - region->base) / region->block_size; > > > + nbits = DIV_ROUND_UP(len, region->block_size); > > > + return find_next_zero_bit(region->blk_bitmap, nr + nbits, nr) == nr + nbits; > > I'm not sure how this works... Is it taking a size or an end point? > > > > Linux equivalent takes size, so I'd expect > > > > return find_next_zero_bit(region->blk_bitmap, nbits, nr); > > Perhaps a comment would avoid any future confusion on this. > > > > My understanding is that the size is the size of the bitmap, which is > also end of the range to check, not the length of the range to check. > > The function find_next_zero_bit(bitmap, size, offset) checks the bitmap range > [offset, size) to find the next unset bit, for the above test, we want to > check range [nr, nr + nbits), so the arguments passed to the function > should be right. > > In the definition of the function, whenever offset >= size, it returns size > because size is the end of the range, So if we pass nbits and nr > to the function and nr >= nbits, which can be common, meaning (dpa-region_base) > \> len, the function will always return true; that is not what we want. > > To sum up, the second parameter of the function should always be the end > of the range to check, for our case, it is nr + nbits. Ok. Thanks for the explanation. That sounds good to me Jonathan > > Fan