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 DFCBD3C478 for ; Mon, 12 Feb 2024 15:34:50 +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=1707752092; cv=none; b=SG375eZ66H1uGyBvPbSXMN2+iAewDvXUVdmgmj+CZTM2zrGMabFF4pqL7NzHd21xGiaPDuKHJaApgwL/8phc+nlgdaz9xv0Tm/168ysoPIqeDBdeGKOOpEopt/znnD+WoUkrSoPK5Izc+fbT1S5fm9685izPpZV9IrbyRWDRzXk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707752092; c=relaxed/simple; bh=fDYaR6n0CYl6u9/RTHsHKwhIKw3nTGbXvq3+M6mhgh0=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=KchOIHxE/xsUkKUJP+kWRUBK06g10C+lLffWnzfQascELWuVoj0+WQDL6QY6IBrnVEGoxw9k8/Fmnh5TIOzKH3qW4mPJAd7euS2gFX/+YAnVa4BmGT5k5se0UQlUPeS+4tJLQnA8lBYcbfZdZ+nfh8nMBeWNTZuQHiKfh5FsC68= 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 600FDDA7; Mon, 12 Feb 2024 07:35:31 -0800 (PST) Received: from [10.57.78.115] (unknown [10.57.78.115]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9D37C3F766; Mon, 12 Feb 2024 07:34:45 -0800 (PST) Message-ID: Date: Mon, 12 Feb 2024 15:34:43 +0000 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 19/25] arm64/mm: Wire up PTE_CONT for user mappings Content-Language: en-GB To: David Hildenbrand , Mark Rutland Cc: Catalin Marinas , Will Deacon , Ard Biesheuvel , Marc Zyngier , James Morse , Andrey Ryabinin , Andrew Morton , Matthew Wilcox , Kefeng Wang , John Hubbard , Zi Yan , Barry Song <21cnbao@gmail.com>, Alistair Popple , Yang Shi , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , linux-arm-kernel@lists.infradead.org, x86@kernel.org, linuxppc-dev@lists.ozlabs.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240202080756.1453939-1-ryan.roberts@arm.com> <20240202080756.1453939-20-ryan.roberts@arm.com> <502a3ea7-fd86-4314-8292-c7999eda92eb@arm.com> <427ba87a-7dd0-4f3e-861f-fe6946b7cd97@redhat.com> From: Ryan Roberts In-Reply-To: <427ba87a-7dd0-4f3e-861f-fe6946b7cd97@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12/02/2024 15:26, David Hildenbrand wrote: > On 12.02.24 15:45, Ryan Roberts wrote: >> On 12/02/2024 13:54, David Hildenbrand wrote: >>>>> If so, I wonder if we could instead do that comparison modulo the access/dirty >>>>> bits, >>>> >>>> I think that would work - but will need to think a bit more on it. >>>> >>>>> and leave ptep_get_lockless() only reading a single entry? >>>> >>>> I think we will need to do something a bit less fragile. ptep_get() does >>>> collect >>>> the access/dirty bits so its confusing if ptep_get_lockless() doesn't IMHO. So >>>> we will likely want to rename the function and make its documentation explicit >>>> that it does not return those bits. >>>> >>>> ptep_get_lockless_noyoungdirty()? yuk... Any ideas? >>>> >>>> Of course if I could convince you the current implementation is safe, I >>>> might be >>>> able to sidestep this optimization until a later date? >>> >>> As discussed (and pointed out abive), there might be quite some callsites where >>> we don't really care about uptodate accessed/dirty bits -- where ptep_get() is >>> used nowadays. >>> >>> One way to approach that I had in mind was having an explicit interface: >>> >>> ptep_get() >>> ptep_get_uptodate() >>> ptep_get_lockless() >>> ptep_get_lockless_uptodate() >> >> Yes, I like the direction of this. I guess we anticipate that call sites >> requiring the "_uptodate" variant will be the minority so it makes sense to use >> the current names for the "_not_uptodate" variants? But to do a slow migration, >> it might be better/safer to have the weaker variant use the new name - that >> would allow us to downgrade one at a time? > > Yes, I was primarily struggling with names. Likely it makes sense to either have > two completely new function names, or use the new name only for the "faster but > less precise" variant. > >> >>> >>> Especially the last one might not be needed. >> I've done a scan through the code and agree with Mark's original conclusions. >> Additionally, huge_pte_alloc() (which isn't used for arm64) doesn't rely on >> access/dirty info. So I think I could migrate everything to the weaker variant >> fairly easily. >> >>> >>> Futher, "uptodate" might not be the best choice because of PageUptodate() and >>> friends. But it's better than "youngdirty"/"noyoungdirty" IMHO. >> >> Certainly agree with "noyoungdirty" being a horrible name. How about "_sync" / >> "_nosync"? > > I could live with > > ptep_get_sync() > ptep_get_nosync() > > with proper documentation :) but could you live with: ptep_get() ptep_get_nosync() ptep_get_lockless_nosync() ? So leave the "slower, more precise" version with the existing name. > > I don't think we use "_sync" / "_nosync" in the context of pte operations yet. > > Well, there seems to be "__arm_v7s_pte_sync" in iommu code, bit at least in core > code nothing jumped at me. >