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Message-ID: <6ada635e-973d-4e32-ab47-1fda12ee7ce7@efficios.com> Date: Fri, 21 Feb 2025 14:38:30 -0500 From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com> To: Dave Hansen <dave.hansen@...el.com>, Dmitry Vyukov <dvyukov@...gle.com>, peterz@...radead.org, boqun.feng@...il.com, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, hpa@...or.com, aruna.ramakrishna@...cle.com, elver@...gle.com Cc: "Paul E. McKenney" <paulmck@...nel.org>, x86@...nel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 3/4] rseq: Make rseq work with protection keys On 2025-02-21 12:17, Dave Hansen wrote: > On 2/17/25 03:07, Dmitry Vyukov wrote: [...] > This code flow is a bit hard to follow with the retry and all. > > I think the assumption here is that overwriting the pkey register is too > slow for the fast path. Instead, in the slow error path, there is a > one-time operation to make the register permissive and retry. > > I guess it's your rseq code. But I'd probably just put the > switch_to_permissive_pkey_reg()/write_pkey_reg() in the fast/common path > for simplicity unless I knew it was causing a measurable performance > problem. I agree that switching to permissive key in the fast path would be simpler. AFAIU, the switch_to_permissive_pkey_reg() is only a pkey read when the key is already permissive. I'd favor the simpler approach unless performance end up being an issue. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com
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