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[124.171.83.152]) by smtp.gmail.com with ESMTPSA id s198sm3607567pgc.4.2020.08.27.18.51.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 27 Aug 2020 18:51:18 -0700 (PDT) Subject: Re: [PATCH v1 04/10] powerpc/kernel/iommu: Add new iommu_table_in_use() helper To: Leonardo Bras , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Christophe Leroy , Joel Stanley , Thiago Jung Bauermann , Ram Pai , Brian King , Murilo Fossa Vicentini , David Dai Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org References: <20200817234033.442511-1-leobras.c@gmail.com> <20200817234033.442511-5-leobras.c@gmail.com> <5f26d433abcde7cd3b4da705742e17ca6c0f0f0b.camel@gmail.com> From: Alexey Kardashevskiy Autocrypt: addr=aik@ozlabs.ru; keydata= mQINBE+rT0sBEADFEI2UtPRsLLvnRf+tI9nA8T91+jDK3NLkqV+2DKHkTGPP5qzDZpRSH6mD EePO1JqpVuIow/wGud9xaPA5uvuVgRS1q7RU8otD+7VLDFzPRiRE4Jfr2CW89Ox6BF+q5ZPV /pS4v4G9eOrw1v09lEKHB9WtiBVhhxKK1LnUjPEH3ifkOkgW7jFfoYgTdtB3XaXVgYnNPDFo 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ZhSFtHopZnBSCUSNDbB+QGy4B/E++Bb02IBTGl/JxmOwG+kZUnymsPvTtnNIeTLHxN/H/ae0 c7E5M+/NpslPCmYnDjs5qg0/3ihh6XuOGggZQOqrYPC3PnsNs3NxirwOkVPQgO6mXxpuifvJ DG9EMkK8IBXnLulqVk54kf7fE0jT/d8RTtJIA92GzsgdK2rpT1MBKKVffjRFGwN7nQVOzi4T XrB5p+6ML7Bd84xOEGsj/vdaXmz1esuH7BOZAGEZfLRCHJ0GVCSssg== Message-ID: <3b7bd273-6ae1-9e7d-a946-fd9380cd2ccc@ozlabs.ru> Date: Fri, 28 Aug 2020 11:51:11 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <5f26d433abcde7cd3b4da705742e17ca6c0f0f0b.camel@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 28/08/2020 04:34, Leonardo Bras wrote: > On Sat, 2020-08-22 at 20:34 +1000, Alexey Kardashevskiy wrote: >>> + >>> + /*ignore reserved bit0*/ >> >> s/ignore reserved bit0/ ignore reserved bit0 / (add spaces) > > Fixed > >>> + if (tbl->it_offset == 0) >>> + p1_start = 1; >>> + >>> + /* Check if reserved memory is valid*/ >> >> A missing space here. > > Fixed > >> >>> + if (tbl->it_reserved_start >= tbl->it_offset && >>> + tbl->it_reserved_start <= (tbl->it_offset + tbl->it_size) && >>> + tbl->it_reserved_end >= tbl->it_offset && >>> + tbl->it_reserved_end <= (tbl->it_offset + tbl->it_size)) { >> >> Uff. What if tbl->it_reserved_end is bigger than tbl->it_offset + >> tbl->it_size? >> >> The reserved area is to preserve MMIO32 so it is for it_offset==0 only >> and the boundaries are checked in the only callsite, and it is unlikely >> to change soon or ever. >> >> Rather that bothering with fixing that, may be just add (did not test): >> >> if (WARN_ON(( >> (tbl->it_reserved_start || tbl->it_reserved_end) && (it_offset != 0)) >> (tbl->it_reserved_start > it_offset && tbl->it_reserved_end < it_offset >> + it_size) && (it_offset == 0)) ) >> return true; >> >> Or simply always look for it_offset..it_reserved_start and >> it_reserved_end..it_offset+it_size and if there is no reserved area, >> initialize it_reserved_start=it_reserved_end=it_offset so the first >> it_offset..it_reserved_start becomes a no-op. > > The problem here is that the values of it_reserved_{start,end} are not > necessarily valid. I mean, on iommu_table_reserve_pages() the values > are stored however they are given (bit reserving is done only if they > are valid). > > Having a it_reserved_{start,end} value outside the valid ranges would > cause find_next_bit() to run over memory outside the bitmap. > Even if the those values are < tbl->it_offset, the resulting > subtraction on unsigned would cause it to become a big value and run > over memory outside the bitmap. > > But I think you are right. That is not the place to check if the > reserved values are valid. It should just trust them here. > I intent to change iommu_table_reserve_pages() to only store the > parameters in it_reserved_{start,end} if they are in the range, and or > it_offset in both of them if they are not. > > What do you think? This should work, yes. > > Thanks for the feedback! > Leonardo Bras > > > -- Alexey