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 925E130BBB8 for ; Mon, 2 Mar 2026 17:56:14 +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=1772474176; cv=none; b=foUIc1Drey7WkptkS6Ywba4GbgxwmEWsEpG9u0J02UeAn8fVwwvKTlcEQKdZHrWpfslKFUU5+HTWlA+ifAvmupUD/tRi1qZaiBp28l07ypiN3mLn7iRCbwWlgcKlf81YlVgb9nns/8UDVN66LFUrZfd+3JJ+eItVp5Lo8L0Yyq4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772474176; c=relaxed/simple; bh=PkeZ8y0bkcwqMRkujPxPp0fF6v5fKlQBgKA7nxLdsGg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=q3JlmLUN2rAd7efs0mhDyQNkcoloX2awcs9EOaklhO2Cs4lpm2r3hkjFKrp3RIix8xGs091rgPhex4eBtwMhlvJ4m9lcOohtNnXR8Q1opSGPtvpjysszNwmz5IYT8CKgKsZEHlmxt6lWfvYGiAmw6hMzRSBAyDCgOIyWOQiKJ5M= 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 DC94814BF; Mon, 2 Mar 2026 09:56:01 -0800 (PST) Received: from J2N7QTR9R3 (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F061E3F73B; Mon, 2 Mar 2026 09:56:05 -0800 (PST) Date: Mon, 2 Mar 2026 17:56:00 +0000 From: Mark Rutland To: Ryan Roberts Cc: Will Deacon , Ard Biesheuvel , Catalin Marinas , Linus Torvalds , Oliver Upton , Marc Zyngier , Dev Jain , Linu Cherian , Jonathan Cameron , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 13/13] arm64: mm: Provide level hint for flush_tlb_page() Message-ID: References: <20260302135602.3716920-1-ryan.roberts@arm.com> <20260302135602.3716920-14-ryan.roberts@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: On Mon, Mar 02, 2026 at 05:39:51PM +0000, Ryan Roberts wrote: > On 02/03/2026 14:42, Mark Rutland wrote: > > On Mon, Mar 02, 2026 at 01:56:00PM +0000, Ryan Roberts wrote: > >> Previously tlb invalidations issued by __flush_tlb_page() did not > >> contain a level hint. But the function is clearly only ever targeting > >> level 3 tlb entries and its documentation agrees: > >> > >> | this operation only invalidates a single, last-level page-table > >> | entry and therefore does not affect any walk-caches > > > > FWIW, I'd have read "last-level" as synonymous with "leaf" (i.e. a Page > > or Block entry, which is the last level of walk) rather than level 3 > > specifically. The architecture uses the term to match the former (e.g. > > in the description of TLBI VALE1IS). > > Hmm yeah, now that I'm re-reading, I agree that quoted documentation doesn't say > anything about it being level 3 specific. > > But actually that was arm64-specific documentation for flush_tlb_page(), which > is a core-mm function. The generic docs at Documentation/core-api/cachetlb.rst > make it clear that it's intended only for PTE invalidations, I think: > > | 4) ``void flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)`` > | > | This time we need to remove the PAGE_SIZE sized translation > | from the TLB. ... Ah! I agree that's stronger and clearer. > > If we're tightening up __flush_tlb_page(), I think it'd be worth either > > updating the comment to explicitly note that this only applies to level > > 3 entries, OR update the comment+name to say it applies to leaf entries, > > and have it take a level parameter. > > I'll fix the arm64-specific docs to align with the generic docs and replace > "last-level" with "level 3" if that works for you. Yep, saying "level 3" definitely works for me -- I just want this to be explicit either way to minimize risk of confusion. [...] > >> However, it turns out that the function was actually being used to > >> invalidate a level 2 mapping via flush_tlb_fix_spurious_fault_pmd(). > >> The bug was benign because the level hint was not set so the HW would > >> still invalidate the PMD mapping, and also because the TLBF_NONOTIFY > >> flag was set, the bounds of the mapping were never used for anything > >> else. > > > > I suspect (as above) that the current usage was intentional, legitimate > > usage, just poorly documented. > > Before this series flush_tlb_fix_spurious_fault_pmd() was implemented using > local_flush_tlb_page_nonotify() which never even gives an option to set the TTL > hint, so I agree. > > But I don't think flush_tlb_fix_spurious_fault_pmd() should be calling any tlb > flush api that has "page" in the name since that implies PTE, not PMD. > > I think what I have done is an improvement; but I'm happy to soften/correct this > description in the next version. I think if you include the quote from the core API documentation above, the rest is is good as is, and doesn't need to be softened. > >> Now that we have the new and improved range-invalidation API, it is > >> trival to fix flush_tlb_fix_spurious_fault_pmd() to explicitly flush the > >> whole range (locally, without notification and last level only). So > >> let's do that, and then update __flush_tlb_page() to hint level 3. > > > > Do we never use __flush_tlb_page() to manipulate a level 1 block > > mapping? I'd have expected we did the same lazy invalidation for > > permission relazation there, but if that's not the case, then this seems > > fine in principle. > > No, there is no flush_tlb_fix_spurious_fault_pud(). > (flush_tlb_fix_spurious_fault_pmd() was only added last cycle). Thanks for confirming; I just wasn't sure whether that didn't exist or whether it had been possibly missed. [...] > >> -#define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp) \ > >> - __flush_tlb_page(vma, address, TLBF_NOBROADCAST | TLBF_NONOTIFY) > >> +#define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp) \ > >> + __flush_tlb_range(vma, address, address + PMD_SIZE, PMD_SIZE, 2, \ > >> + TLBF_NOBROADCAST | TLBF_NONOTIFY | TLBF_NOWALKCACHE) > > > > Is there a reason to keep __flush_tlb_page(), rather than defining > > flush_tlb_fix_spurious_fault() in terms of __flush_tlb_range() with all > > the level 3 constants? > > __flush_tlb_page() is called by __ptep_clear_flush_young() and > __ptep_set_access_flags() (as well as by flush_tlb_page()). I could replace them > all, but __flush_tlb_page() is a bit less verbose... I have no strong preference. That's reason enough to keep it; thanks for confirming, and sorry for the noise! Mark.