From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2FBA98E; Mon, 11 Dec 2023 08:13:45 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 44658FEC; Mon, 11 Dec 2023 08:14:31 -0800 (PST) Received: from [10.57.85.194] (unknown [10.57.85.194]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7959B3F738; Mon, 11 Dec 2023 08:13:39 -0800 (PST) Message-ID: Date: Mon, 11 Dec 2023 16:13:38 +0000 Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/7] ACPI/IORT: Handle memory address size limits as limits Content-Language: en-GB To: Mark Rutland , Will Deacon Cc: Joerg Roedel , Christoph Hellwig , Vineet Gupta , Russell King , Catalin Marinas , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Suravee Suthikulpanit , David Woodhouse , Lu Baolu , Niklas Schnelle , Matthew Rosato , Gerald Schaefer , Jean-Philippe Brucker , Rob Herring , Frank Rowand , Marek Szyprowski , Jason Gunthorpe , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, iommu@lists.linux.dev, devicetree@vger.kernel.org References: <2ae6199a9cf035c1defd42e48675b827f41cdc95.1701268753.git.robin.murphy@arm.com> <20231211132757.GE25681@willie-the-truck> <91b22090-485f-49c9-a536-849fd7f92f8e@arm.com> <20231211153023.GA26048@willie-the-truck> From: Robin Murphy In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2023-12-11 3:39 pm, Mark Rutland wrote: > On Mon, Dec 11, 2023 at 03:30:24PM +0000, Will Deacon wrote: >> On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: >>> On 2023-12-11 1:27 pm, Will Deacon wrote: >>>> On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: >>>>> Return the Root Complex/Named Component memory address size limit as an >>>>> inclusive limit value, rather than an exclusive size. This saves us >>>>> having to special-case 64-bit overflow, and simplifies our caller too. >>>>> >>>>> Signed-off-by: Robin Murphy >>>>> --- >>>>> drivers/acpi/arm64/dma.c | 9 +++------ >>>>> drivers/acpi/arm64/iort.c | 18 ++++++++---------- >>>>> include/linux/acpi_iort.h | 4 ++-- >>>>> 3 files changed, 13 insertions(+), 18 deletions(-) >>>> >>>> [...] >>>> >>>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c >>>>> index 6496ff5a6ba2..eb64d8e17dd1 100644 >>>>> --- a/drivers/acpi/arm64/iort.c >>>>> +++ b/drivers/acpi/arm64/iort.c >>>>> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) >>>>> { return -ENODEV; } >>>>> #endif >>>>> -static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> +static int nc_dma_get_range(struct device *dev, u64 *limit) >>>>> { >>>>> struct acpi_iort_node *node; >>>>> struct acpi_iort_named_component *ncomp; >>>>> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> return -EINVAL; >>>>> } >>>>> - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : >>>>> - 1ULL<memory_address_limit; >>>>> + *limit = (1ULL << ncomp->memory_address_limit) - 1; >>>> >>>> The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe >>>> to drop that? You mention it in the cover letter, so clearly I'm missing >>>> something! >>> >>> Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus >>> subtracting 1 results in the correct all-bits-set value for an inclusive >>> 64-bit limit. >> >> Oh, I'd have thought you'd have gotten one of those "left shift count >= >> width of type" warnings if you did that. > > I think you'll get a UBSAN splat, but here the compiler doesn't know what > 'ncomp->memory_address_limit' will be and so doesn't produce a compile-time > warning. > > Regardless, it's undefined behaviour. Urgh, you're right... I double-checked 6.5.7.4 in the standard but managed to miss 6.5.7.3. So yeah, even though "4 << 62" or "2 << 63" are well-defined here, "1 << 64" isn't, dang. Thanks, funky old ISAs which did weird things for crazy large shifts and have no relevance to this code :( Cheers, Robin. 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 879B5C10F05 for ; Mon, 11 Dec 2023 16:14:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:Content-Type: Content-Transfer-Encoding:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:From:References:Cc:To:Subject: MIME-Version:Date:Message-ID:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=uzOMp2dgiGXqeoIQC0e5rzNPd1UYjuHhYJ6d6qrz2lk=; b=YPrDR0rCR4T7WW bG1WI15yFKwqzWEON65/kMdSmsAIHVyk9Vh/Y7qBSklw6jP2bvb3Pq6u41vkxt9uSor5Hl/qExT0e SeDqBhg8DmHLUnojCZdOGpo8iQG14BYmyDZr0VMbpeLt48AyjJk5M4e8najhx+7WJjDOL6FL4ybFG fjJhxzRSfNaATYbDcXkqmUxPRjxFismbZioUWza8fLPLKYPwet9MDBWj2+S/BX9pPHSa5a4CTH5+B yg7JXuy4ZxGRSzkKxsgmV/sxGrWHbHehABK/zuCptVuvymYHZ2vPgfDCxYjQLLqswaXeIJNvfDErf o1h0kgJKIjBlTbsMBzNA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rCiup-005hO2-2w; Mon, 11 Dec 2023 16:13:55 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1rCiuj-005hKG-1Y for linux-arm-kernel@lists.infradead.org; Mon, 11 Dec 2023 16:13:54 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 44658FEC; Mon, 11 Dec 2023 08:14:31 -0800 (PST) Received: from [10.57.85.194] (unknown [10.57.85.194]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 7959B3F738; Mon, 11 Dec 2023 08:13:39 -0800 (PST) Message-ID: Date: Mon, 11 Dec 2023 16:13:38 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/7] ACPI/IORT: Handle memory address size limits as limits Content-Language: en-GB To: Mark Rutland , Will Deacon Cc: Joerg Roedel , Christoph Hellwig , Vineet Gupta , Russell King , Catalin Marinas , Huacai Chen , WANG Xuerui , Thomas Bogendoerfer , Paul Walmsley , Palmer Dabbelt , Albert Ou , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , "K. Y. Srinivasan" , Haiyang Zhang , Wei Liu , Dexuan Cui , Suravee Suthikulpanit , David Woodhouse , Lu Baolu , Niklas Schnelle , Matthew Rosato , Gerald Schaefer , Jean-Philippe Brucker , Rob Herring , Frank Rowand , Marek Szyprowski , Jason Gunthorpe , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org, iommu@lists.linux.dev, devicetree@vger.kernel.org References: <2ae6199a9cf035c1defd42e48675b827f41cdc95.1701268753.git.robin.murphy@arm.com> <20231211132757.GE25681@willie-the-truck> <91b22090-485f-49c9-a536-849fd7f92f8e@arm.com> <20231211153023.GA26048@willie-the-truck> From: Robin Murphy In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231211_081349_630343_E032BCBD X-CRM114-Status: GOOD ( 16.55 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2023-12-11 3:39 pm, Mark Rutland wrote: > On Mon, Dec 11, 2023 at 03:30:24PM +0000, Will Deacon wrote: >> On Mon, Dec 11, 2023 at 03:01:27PM +0000, Robin Murphy wrote: >>> On 2023-12-11 1:27 pm, Will Deacon wrote: >>>> On Wed, Nov 29, 2023 at 05:43:00PM +0000, Robin Murphy wrote: >>>>> Return the Root Complex/Named Component memory address size limit as an >>>>> inclusive limit value, rather than an exclusive size. This saves us >>>>> having to special-case 64-bit overflow, and simplifies our caller too. >>>>> >>>>> Signed-off-by: Robin Murphy >>>>> --- >>>>> drivers/acpi/arm64/dma.c | 9 +++------ >>>>> drivers/acpi/arm64/iort.c | 18 ++++++++---------- >>>>> include/linux/acpi_iort.h | 4 ++-- >>>>> 3 files changed, 13 insertions(+), 18 deletions(-) >>>> >>>> [...] >>>> >>>>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c >>>>> index 6496ff5a6ba2..eb64d8e17dd1 100644 >>>>> --- a/drivers/acpi/arm64/iort.c >>>>> +++ b/drivers/acpi/arm64/iort.c >>>>> @@ -1367,7 +1367,7 @@ int iort_iommu_configure_id(struct device *dev, const u32 *input_id) >>>>> { return -ENODEV; } >>>>> #endif >>>>> -static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> +static int nc_dma_get_range(struct device *dev, u64 *limit) >>>>> { >>>>> struct acpi_iort_node *node; >>>>> struct acpi_iort_named_component *ncomp; >>>>> @@ -1384,13 +1384,12 @@ static int nc_dma_get_range(struct device *dev, u64 *size) >>>>> return -EINVAL; >>>>> } >>>>> - *size = ncomp->memory_address_limit >= 64 ? U64_MAX : >>>>> - 1ULL<memory_address_limit; >>>>> + *limit = (1ULL << ncomp->memory_address_limit) - 1; >>>> >>>> The old code handled 'ncomp->memory_address_limit >= 64' -- why is it safe >>>> to drop that? You mention it in the cover letter, so clearly I'm missing >>>> something! >>> >>> Because an unsigned shift by 64 or more generates 0 (modulo 2^64), thus >>> subtracting 1 results in the correct all-bits-set value for an inclusive >>> 64-bit limit. >> >> Oh, I'd have thought you'd have gotten one of those "left shift count >= >> width of type" warnings if you did that. > > I think you'll get a UBSAN splat, but here the compiler doesn't know what > 'ncomp->memory_address_limit' will be and so doesn't produce a compile-time > warning. > > Regardless, it's undefined behaviour. Urgh, you're right... I double-checked 6.5.7.4 in the standard but managed to miss 6.5.7.3. So yeah, even though "4 << 62" or "2 << 63" are well-defined here, "1 << 64" isn't, dang. Thanks, funky old ISAs which did weird things for crazy large shifts and have no relevance to this code :( Cheers, Robin. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel