From mboxrd@z Thu Jan 1 00:00:00 1970 From: Leo Liang Date: Thu, 14 Oct 2021 17:40:40 +0800 Subject: [OpenSBI] rfence related question Message-ID: List-Id: To: opensbi@lists.infradead.org MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Hi, I am studying the rfence part of OpenSBI recently. >From what I understand the mechanism of the IPI framework is to do "update" to update the IPI information for remote harts, and then send IPI through "ipi_dev" device to remote harts sequentially. After the first IPI is sent (let's say from hart 0 to hart 1), hart 0 waits in the "sync" for the remote hart(hart 1) to do "process". Hart 0 waits until the per hart tlb_sync flag is set from the remote hart(hart1) after "process" is done, and then keep on sending the next IPI to hart 2, and then hart 3 ... etc. If I understand it correctly, then would the following scenario have the possibility to occur? In Linux, Hart 0 executes remote I cache flush instruction and sends IPI to hart 1; At the meantime, hart 2 executes the same instruction and tries to send IPI to hart 0. Both hart 0 and hart 2 step into m-mode, their mstatus.mie are disabled, so, when hart 0 tries to send IPI to hart 2 and wait for the sync, deadlock happens. Hart 0 is waiting for hart 2 and hart 2 is also waiting for hart 0 indefinitely because the interrupts being disabled. Is this case likely to happen? Best regards, Leo