From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from fanzine2.igalia.com (fanzine2.igalia.com [213.97.179.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 10B2F35B137; Mon, 27 Apr 2026 16:27:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=213.97.179.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777307241; cv=none; b=GtvszSFmuXpk+270xD8wjGUmkksGgfYTxd4oGpxSc4Xsq/mKiul7grSSf2R3JczJ1rYBx1AsCpHVW07RX6odtEDtJo9oH4Y31pY6HItNpqCExFx031U3dqIJfsBtgdmBvukLqTp24EdyDsuuF+9Wwrt2FAhPP6ePUPNS8ULFgN0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777307241; c=relaxed/simple; bh=6KT2lBRYaSdwASapXaVtu5KBdK0QefH/+15iWad9gK4=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=TeKPGon+Gd8TDsR5Nv0AMPXJ3Yph3pJ4d4gcYyTiixo8Ru68T0uHafVjmECeDtKZpF4QQX2bpkN5WvsBaW6OLXcbdS7qJk3ZqXky5sJWVtZlgrCPWQhz+4A6j4GEbLAH1gdRYXn1ZlMQT0S6p3tGSjFASRc9qB5eDKkpusIir1w= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com; spf=pass smtp.mailfrom=igalia.com; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b=syAv4LxL; arc=none smtp.client-ip=213.97.179.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=igalia.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=igalia.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=igalia.com header.i=@igalia.com header.b="syAv4LxL" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=igalia.com; s=20170329; h=Content-Transfer-Encoding:Content-Type:In-Reply-To:From: References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender:Reply-To: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help:List-Unsubscribe: List-Subscribe:List-Post:List-Owner:List-Archive; bh=BPLg1Hn38x8a+m0kG/FEsTFwbBhtL+oRHiLJRGc//TU=; b=syAv4LxLVHacKb7lD0gWSxExjl ALtxi4r+F+lwos9dX87zDCmRI8yf5uNew32TzulCab9e3SiknlZyLkTPxwJOt3ooYyt5nNCvzcHBL 74B9Wuq45vZpqBLllROZa3rb7YNwvpc5gNJvkZHgyqmqIolWtVH6rvQGMmtK/Yt1AQkh0DVg1jBv9 9rCLpB8OnLdSdRVKagAZ4q8RrBxZcRDnVMUiArOoGqRQrxAYe1LFin8JRjZCf8R8Ptd+DE4cRa8eH O/7yQfz+ZKhu9ou3cQoawCioTZ9Lp/+H86NE3rdehuB6RIn8Qg3/jQPJEKkuBWXpHPULfWOFNoVva pi2tC98Q==; Received: from [187.57.76.96] (helo=[192.168.15.100]) by fanzine2.igalia.com with esmtpsa (Cipher TLS1.3:ECDHE_X25519__RSA_PSS_RSAE_SHA256__AES_128_GCM:128) (Exim) id 1wHOnL-0030S7-FA; Mon, 27 Apr 2026 18:26:50 +0200 Message-ID: Date: Mon, 27 Apr 2026 13:26:41 -0300 Precedence: bulk X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 2/2] arm64: vdso: Implement __vdso_futex_robust_try_unlock() To: =?UTF-8?Q?Thomas_Wei=C3=9Fschuh?= Cc: Catalin Marinas , Will Deacon , Thomas Gleixner , Mark Rutland , Mathieu Desnoyers , Sebastian Andrzej Siewior , Carlos O'Donell , Peter Zijlstra , Florian Weimer , Rich Felker , Torvald Riegel , Darren Hart , Ingo Molnar , Davidlohr Bueso , Arnd Bergmann , "Liam R . Howlett" , Uros Bizjak , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, kernel-dev@igalia.com References: <20260424-tonyk-robust_arm-v2-0-db4e46f752cf@igalia.com> <20260424-tonyk-robust_arm-v2-2-db4e46f752cf@igalia.com> <7ddc1c74-c504-44c6-8d51-d10d436c0db8@t-8ch.de> Content-Language: en-US From: =?UTF-8?Q?Andr=C3=A9_Almeida?= In-Reply-To: <7ddc1c74-c504-44c6-8d51-d10d436c0db8@t-8ch.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Em 26/04/2026 15:30, Thomas Weißschuh escreveu: > On 2026-04-24 15:56:01-0300, André Almeida wrote: > (...) > >> Signed-off-by: André Almeida >> --- >> RFC: >> - Should I duplicate the explanation found in the x86 commit or can I just >> point to it? >> - Only LL/SC for now but I can add LSE later if this looks good >> - It the objdump I see that op_pending is store at x2. But how stable is this, >> how can I write it in a way that's always x2? >> --- >> arch/arm64/Kconfig | 1 + >> arch/arm64/include/asm/futex_robust.h | 35 +++++++++++++ >> arch/arm64/kernel/vdso/Makefile | 9 +++- >> arch/arm64/kernel/vdso/vdso.lds.S | 4 ++ >> .../kernel/vdso/vfutex_robust_list_try_unlock.c | 59 ++++++++++++++++++++++ >> 5 files changed, 107 insertions(+), 1 deletion(-) > > What about the actual 32-bit vDSO in arch/arm64/kernel/vdso32/ ? > Right, I missed that. Then I should move __vdso_futex_robust_list32_try_unlock() to arch/arm64/kernel/vdso32/ right? > (...) > >> diff --git a/arch/arm64/kernel/vdso/vfutex_robust_list_try_unlock.c b/arch/arm64/kernel/vdso/vfutex_robust_list_try_unlock.c >> new file mode 100644 >> index 000000000000..e8a8fb22a2fa >> --- /dev/null >> +++ b/arch/arm64/kernel/vdso/vfutex_robust_list_try_unlock.c >> @@ -0,0 +1,59 @@ >> +// SPDX-License-Identifier: GPL-2.0-or-later >> +#include >> +#include >> + >> +#define LABEL(name, sz) __stringify(__futex_list##sz##_try_unlock_cs_##name) > > We should have some defines for these symbols. While they are not > userspace ABI, they will be used by the selftests. > Do you mean to have this defined at include/uapi/linux/futex.h? >> +#define GLOBLS(sz) ".globl " LABEL(start, sz) ", " LABEL(success, sz) ", " LABEL(end, sz) "\n" >> + >> +__u32 __vdso_futex_robust_list64_try_unlock(__u32 *lock, __u32 tid, __u64 *pop) >> +{ >> + __u32 val, result; >> + >> + asm volatile ( >> + GLOBLS(64) >> + " prfm pstl1strm, %[lock] \n" >> + LABEL(start, 64)": \n" >> + " ldxr %[val], %[lock] \n" >> + " cmp %[tid], %[val] \n" >> + " bne " LABEL(end, 64)" \n" >> + " stlxr %w[result], xzr, %[lock] \n" >> + " cbnz %w[result], " LABEL(start, 64)" \n" >> + LABEL(success, 64)": \n" >> + " str xzr, %[pop] \n" >> + LABEL(end, 64)": \n" >> + >> + : [val] "=&r" (val), [result] "=r" (result) >> + : [tid] "r" (tid), [lock] "Q" (*lock), [pop] "Q" (*pop) >> + : "memory" >> + ); > > My clang 22.1.3 chokes on the assembly in this patch. > Do you mind sharing the output? >> + >> + return val; >> +} >> + >> +#ifdef CONFIG_COMPAT_VDSO > > I am wondering about the CONFIG_COMPAT{,_VDSO} dependency here. > As far as I know the list32 variant is meant to be used by code > emulators which run 32-bit code on a 64-bit kernel, for example FEX. > But these emulators don't actually seem to need CONFIG_COMPAT. > So the dependency does not look correct. > The space savings also should be irrelevant. Right, good catch. In the new syscall I had to do something similar[1], to expose the 32-bit functions to 64-bit kernels as well, and not hide them behind CONFIG_COMPAT. [1] https://lore.kernel.org/lkml/20251122-tonyk-robust_futex-v6-2-05fea005a0fd@igalia.com/ > > The x86 series from Thomas does the same, maybe he will read this > comment, otherwise I'll bring it up on his series, too. > >> +__u32 __vdso_futex_robust_list32_try_unlock(__u32 *lock, __u32 tid, __u32 *pop) >> +{ >> + __u32 val, result; >> + >> + asm volatile ( >> + GLOBLS(32) >> + " prfm pstl1strm, %[lock] \n" >> + LABEL(start, 32)": \n" >> + " ldxr %w[val], %[lock] \n" >> + " cmp %w[tid], %w[val] \n" >> + " bne " LABEL(end, 32)" \n" >> + " stlxr %w[result], wzr, %w[lock] \n" >> + " cbnz %w[result], " LABEL(start, 32)" \n" >> + LABEL(success, 32)": \n" >> + " str wzr, %w[pop] \n" >> + LABEL(end, 32)": \n" >> + >> + : [val] "=&r" (val), [result] "=r" (result) >> + : [tid] "r" (tid), [lock] "Q" (*lock), [pop] "Q" (*pop) >> + : "memory" >> + ); >> + >> + return val; >> +} >> +#endif