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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH 3/4] accel/tcg: Handle false negative lookup in page_check_range Content-Language: en-US To: Richard Henderson , qemu-devel@nongnu.org Cc: iii@linux.ibm.com References: <20221224151821.464455-1-richard.henderson@linaro.org> <20221224151821.464455-4-richard.henderson@linaro.org> From: =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= In-Reply-To: <20221224151821.464455-4-richard.henderson@linaro.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::336; envelope-from=philmd@linaro.org; helo=mail-wm1-x336.google.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 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, NICE_REPLY_A=-1.147, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 24/12/22 16:18, Richard Henderson wrote: > As in page_get_flags, we need to try again with the mmap > lock held if we fail a page lookup. > > Signed-off-by: Richard Henderson > --- > accel/tcg/user-exec.c | 39 ++++++++++++++++++++++++++++++++------- > 1 file changed, 32 insertions(+), 7 deletions(-) > > diff --git a/accel/tcg/user-exec.c b/accel/tcg/user-exec.c > index 2c5c10d2e6..c72a806203 100644 > --- a/accel/tcg/user-exec.c > +++ b/accel/tcg/user-exec.c > @@ -525,6 +525,7 @@ void page_set_flags(target_ulong start, target_ulong end, int flags) > int page_check_range(target_ulong start, target_ulong len, int flags) > { > target_ulong last; > + int locked, ret; have_mmap_lock() returns a boolean, can we declare 'locked' as such, ... > > if (len == 0) { > return 0; /* trivial length */ > @@ -535,42 +536,66 @@ int page_check_range(target_ulong start, target_ulong len, int flags) > return -1; /* wrap around */ > } > > + locked = have_mmap_lock(); > while (true) { > PageFlagsNode *p = pageflags_find(start, last); > int missing; > > if (!p) { > - return -1; /* entire region invalid */ > + if (!locked) { > + /* > + * Lockless lookups have false negatives. > + * Retry with the lock held. > + */ > + mmap_lock(); > + locked = -1; ... skip this confusing assignation, ... > + p = pageflags_find(start, last); > + } > + if (!p) { > + ret = -1; /* entire region invalid */ > + break; > + } > } > if (start < p->itree.start) { > - return -1; /* initial bytes invalid */ > + ret = -1; /* initial bytes invalid */ > + break; > } > > missing = flags & ~p->flags; > if (missing & PAGE_READ) { > - return -1; /* page not readable */ > + ret = -1; /* page not readable */ > + break; > } > if (missing & PAGE_WRITE) { > if (!(p->flags & PAGE_WRITE_ORG)) { > - return -1; /* page not writable */ > + ret = -1; /* page not writable */ > + break; > } > /* Asking about writable, but has been protected: undo. */ > if (!page_unprotect(start, 0)) { > - return -1; > + ret = -1; > + break; > } > /* TODO: page_unprotect should take a range, not a single page. */ > if (last - start < TARGET_PAGE_SIZE) { > - return 0; /* ok */ > + ret = 0; /* ok */ > + break; > } > start += TARGET_PAGE_SIZE; > continue; > } > > if (last <= p->itree.last) { > - return 0; /* ok */ > + ret = 0; /* ok */ > + break; > } > start = p->itree.last + 1; > } > + > + if (locked < 0) { ... and check for !locked here? > + mmap_unlock(); > + } > + return ret; > }