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 B80591D52D for ; Mon, 26 Feb 2024 11:05:27 +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=1708945530; cv=none; b=CvrLMpzw04kNcN8QaTRfpC7Hp476r9MD04u+CybUj1SPqqbrbUhGv3wqgFeg9Xb3taW6P+I4YEhwZ/wH6PU3dFhE6twXGlGcXBYA4NQ/b9unhttQ136Up0rEW4SlXaoyIWoo/amc5SGxswPwJXmGIJukAiB7MQ6nZJxBEU8UvOU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708945530; c=relaxed/simple; bh=Dpvh1u6uIHD3zL72KLsDUAqLNGDPN7ZtBbRRizpzWpw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=cFfQ468zJgZDz7mKOPkaPZVvrpMh4mZtPyGHvEP5Zk/zHrqBSMKrOLbep6G661CywVEJd/Wqy9AU3jL1LphWLVL6tAy8XFIUB7RqoccrFeAEA4nRNVG4iCDFIP25ABmMKaV33+GY04i7CsiJeTsX+dphR0Y09c5ZHsRxKoyptLI= 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; 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 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 A4B9CDA7; Mon, 26 Feb 2024 03:06:03 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.68.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EC98B3F6C4; Mon, 26 Feb 2024 03:05:23 -0800 (PST) Date: Mon, 26 Feb 2024 11:04:46 +0000 From: Mark Rutland To: Anshuman Khandual Cc: Will Deacon , linux-arm-kernel@lists.infradead.org, broonie@kernel.org, Catalin Marinas , linux-kernel@vger.kernel.org Subject: Re: [PATCH] arm64/hw_breakpoint: Determine lengths from generic perf breakpoint macros Message-ID: References: <20240223113102.4027779-1-anshuman.khandual@arm.com> <20240223125224.GC10641@willie-the-truck> <1901fadb-1d71-4374-be8c-00935bb27854@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: <1901fadb-1d71-4374-be8c-00935bb27854@arm.com> On Mon, Feb 26, 2024 at 08:19:39AM +0530, Anshuman Khandual wrote: > On 2/23/24 18:22, Will Deacon wrote: > > On Fri, Feb 23, 2024 at 05:01:02PM +0530, Anshuman Khandual wrote: > >> Both platform i.e ARM_BREAKPOINT_LEN_X and generic i.e HW_BREAKPOINT_LEN_X > >> macros are used interchangeably to convert event->attr.bp_len and platform > >> breakpoint control arch_hw_breakpoint_ctrl->len. Let's be consistent while > >> deriving one from the other. This does not cause any functional changes. > >> > >> Cc: Will Deacon > >> Cc: Mark Rutland > >> Cc: Catalin Marinas > >> Cc: linux-arm-kernel@lists.infradead.org > >> Cc: linux-kernel@vger.kernel.org > >> Signed-off-by: Anshuman Khandual > >> --- > >> This applies on v6.8-rc5 > >> > >> arch/arm64/kernel/hw_breakpoint.c | 16 ++++++++-------- > >> 1 file changed, 8 insertions(+), 8 deletions(-) > >> > >> diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c > >> index 35225632d70a..1ab9fc865ddd 100644 > >> --- a/arch/arm64/kernel/hw_breakpoint.c > >> +++ b/arch/arm64/kernel/hw_breakpoint.c > >> @@ -301,28 +301,28 @@ static int get_hbp_len(u8 hbp_len) > >> > >> switch (hbp_len) { > >> case ARM_BREAKPOINT_LEN_1: > >> - len_in_bytes = 1; > >> + len_in_bytes = HW_BREAKPOINT_LEN_1; > > > > I don't think we should do this. The HW_BREAKPOINT_LEN_* definitions are > > part of the user ABI and, although they correspond to the length in bytes, > > that's not necessarily something we should rely on. > > Why should not we rely on the user ABI macros if these byte lengths were > initially derived from them. Why should we change the clear: len_in_bytes = 1; ... to the longer, and less clear: len_in_bytes = HW_BREAKPOINT_LEN_1; ... ? > But also there are similar conversions in arch_bp_generic_fields(). Those are specifically for converting from the rch_hw_breakpoint_ctrl encodings to the perf_event_attr encodings. There we don't care about the specific value of the byte, just that we're using the correct encoding. > These hard coded raw byte length numbers seems cryptic, where as in reality > these are just inter converted from generic HW breakpoints lengths. There are three distinct concepts here: 1. The length in bytes, as returned above by get_hbp_len() 2. The length as encoded in the ARM_BREAKPOINT_LEN_* encoding 3. The length as encoded in the HW_BREAKPOINT_LEN_* encoding. I think you're arguing that since 1 and 3 happen to have the values we should treat them as the same thing. I think that Will and I believe that they should be kept distinct because they are distinct concepts. I don't think this needs to change, and can be left as-is. Mark.