From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 8CC30361667 for ; Fri, 8 May 2026 14:24:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778250247; cv=none; b=u8jIf88V9o/foUX6XcEfUnn+M8YW3Fs0sLebmxgXI/Z23JhUi0XTYOopAuEyA2MwAc34/O2Mx7xVXsCz5GsnFpgBDD7+j4OYAGaT2LzxBIau33uzgXDXypSiROLDuaSE9G6mXKKq2NtNhtzBAjRSMCXK08dJo3xaJMxdQIBH1dc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778250247; c=relaxed/simple; bh=ey7j9mUyY/5BkGE3ioQIxIOGQe6vQUDgNT0wSP5HSn8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=UyQwteiFEB5w42SwVmiemGbtXbdfP8jx+iBCdUOAnLqDp8Am722Rjr4tre5uG3WieIWzb8zJmE007WSoxdMRXEimWUqzRpMp9F1rAE1BLgnOm56LeqSvKbazThUsALW8X0irsCj6KM+t4f4IeFVDm2Ovi5bqJYf80t8lvbWhZnU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=f//jqe4q; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="f//jqe4q" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 9AF261D34; Fri, 8 May 2026 07:23:59 -0700 (PDT) Received: from arm.com (usa-sjc-mx-foss1.foss.arm.com [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 81B0F3F763; Fri, 8 May 2026 07:24:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1778250244; bh=ey7j9mUyY/5BkGE3ioQIxIOGQe6vQUDgNT0wSP5HSn8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=f//jqe4qjaix8EYoHr4nh8K0vmc4rWVJGmfLkqhRiuebd+7CkHcs6C+F+6HZ/DCMp pDGLbbTUg61TmkBZW38vt1j5M0HcOXhMtiA9CnF790CtCAcwxA0wjVgpMKHEeBMZ7g Sw+4jWoLAH+pQ9aRBO8wLrkRLWD4B3WQtFAV7/p4= Date: Fri, 8 May 2026 15:24:01 +0100 From: Catalin Marinas To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, Peter Zijlstra , Thomas Gleixner , Will Deacon , ckennelly@google.com, dvyukov@google.com, linux-kernel@vger.kernel.org, mathias@mongodb.com, mathieu.desnoyers@efficios.com, ruanjinjie@huawei.com Subject: Re: [PATCHv2] arm64/entry: Fix arm64-specific rseq brokenness Message-ID: References: <20260508142023.3268622-1-mark.rutland@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260508142023.3268622-1-mark.rutland@arm.com> On Fri, May 08, 2026 at 03:20:23PM +0100, Mark Rutland wrote: > Mathias Stearn reports that since v6.19, there are two big issues > affecting rseq: > > (1) On arm64 specifically, rseq critical sections aren't aborted when > they should be. > > (2) The 'cpu_id_start' field is no longer written by the kernel in all > cases it used to be, including some cases where TCMalloc depends on > the kernel clobbering the field. > > This patch fixes issue #1. This patch DOES NOT fix issue #2, which will > need to be addressed by other patches. > > The arm64-specific brokenness is a result of commits: > > 2fc0e4b4126c ("rseq: Record interrupt from user space") > 39a167560a61 ("rseq: Optimize event setting") > > The first commit failed to add a call to rseq_note_user_irq_entry() on > arm64. Thus arm64 never sets rseq_event::user_irq to record that it may > be necessary to abort an active rseq critical section upon return to > userspace. On its own, this commit had no functional impact as the value > of rseq_event::user_irq was not consumed. > > The second commit relied upon rseq_event::user_irq to determine whether > or not to bother to perform rseq work when returning to userspace. As > rseq_event::user_irq wasn't set on arm64, this work would be skipped, > and consequently an active rseq critical section would not be aborted. > > Fix this by giving arm64 syscall-specific entry/exit paths, and > performing the relevant logic in syscall and non-syscall paths, > including calling rseq_note_user_irq_entry() for non-syscall entry. > > Currently arm64 cannot use syscall_enter_from_user_mode(), > syscall_exit_to_user_mode(), and irqentry_exit_to_user_mode(), due to > ordering constraints with exception masking, and risk of ABI breakage > for syscall tracing/audit/etc. For the moment the entry/exit logic is > left as arm64-specific, directly using enter_from_user_mode() and > exit_to_user_mode(), but mirroring the generic code. > > I intend to follow up with refactoring/cleanup, as we did for kernel > mode entry paths in commit: > > 041aa7a85390 ("entry: Split preemption from irqentry_exit_to_kernel_mode()") > > ... which will allow arm64 to use the GENERIC_IRQ_ENTRY functions directly. > > Fixes: 39a167560a61 ("rseq: Optimize event setting") > Reported-by: Mathias Stearn > Link: https://lore.kernel.org/regressions/CAHnCjA25b+nO2n5CeifknSKHssJpPrjnf+dtr7UgzRw4Zgu=oA@mail.gmail.com/ > Signed-off-by: Mark Rutland > Cc: Catalin Marinas > Cc: Chris Kennelly > Cc: Dmitry Vyukov > Cc: Jinjie Ruan > Cc: Mathieu Desnoyers > Cc: Peter Zijlstra > Cc: Thomas Gleixner > Cc: Will Deacon Acked-by: Catalin Marinas