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Mon, 11 Dec 2023 08:46:24 -0800 (PST) Date: Mon, 11 Dec 2023 17:46:19 +0100 From: Andrea Parri To: Mathieu Desnoyers Cc: paulmck@kernel.org, palmer@dabbelt.com, paul.walmsley@sifive.com, aou@eecs.berkeley.edu, mmaas@google.com, hboehm@google.com, striker@us.ibm.com, charlie@rivosinc.com, rehn@rivosinc.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/4] membarrier: riscv: Provide core serializing command Message-ID: References: <20231211094414.8078-1-parri.andrea@gmail.com> <20231211094414.8078-4-parri.andrea@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231211_084626_949147_60C6B000 X-CRM114-Status: GOOD ( 14.62 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org > > /* > > * The membarrier system call requires a full memory barrier > > * after storing to rq->curr, before going back to user-space. > > + * > > + * The barrier is also needed for the SYNC_CORE command when > > + * switching between processes; in particular, on a transition > > + * from a thread belonging to another mm to a thread belonging > > + * to the mm for which a membarrier SYNC_CORE is done on CPU0: > > + * > > + * - [CPU0] sets all bits in the mm icache_stale_mask. > > + * > > + * - [CPU1] store to rq->curr (by the scheduler). > > + * > > + * - [CPU0] loads rq->curr within membarrier and observes > > + * cpu_rq(1)->curr->mm != mm, so the IPI is skipped on > > + * CPU1; this means membarrier relies on switch_mm() to > > + * issue the sync-core. > > + * > > + * - [CPU1] switch_mm() loads icache_stale_mask; if the bit > > + * is zero, switch_mm() may incorrectly skip the sync-core. > > + * > > + * Matches the full barrier in membarrier_private_expedited(). > > There are two full barriers in membarrier_private_expedited(). We > should clearly state which one it matches, and update the associated > barrier to state that it matches this barrier as well. Agreed, will do. Andrea _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv