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([2a00:23c7:df82:3001:2982:11d0:133d:ad80]) by smtp.gmail.com with ESMTPSA id q13-20020a056000136d00b00343e3023fbasm3947358wrz.34.2024.04.06.03.58.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 06 Apr 2024 03:58:03 -0700 (PDT) Message-ID: <6fad8151-4bde-4a02-96fb-27b99d93757f@gmail.com> Date: Sat, 6 Apr 2024 11:58:02 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] xen-hvm: Avoid livelock while handling buffered ioreqs To: Ross Lagerwall , Stefano Stabellini , Anthony Perard , Paul Durrant Cc: xen-devel@lists.xenproject.org, qemu-devel@nongnu.org References: <20240404140833.1557953-1-ross.lagerwall@citrix.com> Content-Language: en-US From: "Durrant, Paul" In-Reply-To: <20240404140833.1557953-1-ross.lagerwall@citrix.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2a00:1450:4864:20::42b; envelope-from=xadimgnik@gmail.com; helo=mail-wr1-x42b.google.com 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, FREEMAIL_FROM=0.001, 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: , Reply-To: paul@xen.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 04/04/2024 15:08, Ross Lagerwall wrote: > A malicious or buggy guest may generated buffered ioreqs faster than > QEMU can process them in handle_buffered_iopage(). The result is a > livelock - QEMU continuously processes ioreqs on the main thread without > iterating through the main loop which prevents handling other events, > processing timers, etc. Without QEMU handling other events, it often > results in the guest becoming unsable and makes it difficult to stop the > source of buffered ioreqs. > > To avoid this, if we process a full page of buffered ioreqs, stop and > reschedule an immediate timer to continue processing them. This lets > QEMU go back to the main loop and catch up. > Do PV backends potentially cause the same scheduling issue (if not using io threads)? > Signed-off-by: Ross Lagerwall > --- > hw/xen/xen-hvm-common.c | 26 +++++++++++++++++--------- > 1 file changed, 17 insertions(+), 9 deletions(-) > Reviewed-by: Paul Durrant