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[174.21.149.226]) by smtp.gmail.com with ESMTPSA id fy21sm2752245pjb.25.2020.05.08.09.57.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 May 2020 09:57:03 -0700 (PDT) Subject: Re: [PATCH v5 04/19] accel/tcg: Adjust probe_access call to page_check_range To: Peter Maydell References: <20200508154359.7494-1-richard.henderson@linaro.org> <20200508154359.7494-5-richard.henderson@linaro.org> From: Richard Henderson Message-ID: <62eca244-78dd-0359-d82b-30089d893d39@linaro.org> Date: Fri, 8 May 2020 09:57:02 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::442; envelope-from=richard.henderson@linaro.org; helo=mail-pf1-x442.google.com X-detected-operating-system: by eggs.gnu.org: No matching host in p0f cache. That's all we know. X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: =?UTF-8?Q?Alex_Benn=c3=a9e?= , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/8/20 9:13 AM, Peter Maydell wrote: > On Fri, 8 May 2020 at 16:44, Richard Henderson > wrote: >> >> We have validated that addr+size does not cross a page boundary. >> Therefore we need to validate exactly one page. We can achieve >> that passing any value 1 <= x <= size to page_check_range. >> >> Passing 1 will simplify the next patch. > > It's not clear to me how it simplifies the next patch, though -- > we have the size right there in the new function which > calls page_check_range(), don't we? So I still don't > understand why we're using '1' -- it isn't allowing > us to avoid passing the size into probe_access_internal(), > because we need to pass it anyway. > > We've gone round this multiple times now so I feel like > I must be missing something here. While probe_access() has a size parameter, probe_access_flags() does not. For probe_access_internal(), I currently have a "fault_size" parameter that gets passed to tlb_fill, which is "size" for probe_access() and 0 for probe_access_flags(). I *could* add another "check_size" parameter to probe_access_internal, to be passed on to page_check_range(). It would be "size" for probe_access() and 1 for probe_access_flags(). But what's the point? Always passing 1 to page_check_range() has the same effect. I feel like I'm missing something with your objection. r~