From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 383882DB7B7; Thu, 23 Apr 2026 19:45:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776973504; cv=none; b=QHUpfgSwd8EwawTCvwGgs0I2vhGX+IGKBmHWNUEQmc9tF+jcIZ595vApBhEZ75n8bezlN3nPI5CMUt+CS5i6WjeDBrN/XoxRtImSXXbk8qZqAyMqTB3RA+h35K9LPhiJiKFble+C2z8T9Fq5v/MrNVvW9PVrMGwrggogw7PtYwc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776973504; c=relaxed/simple; bh=ENC60U4eoLTeOFgHvSyl4mRh0gHFD8ZCM+8UztNm+Oc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=B2s2W+ywfveimjx9jKuCoMIxcH0kcI4GZByU32DGE1eZDlcKYtURKauvVseVVv/TSwYjZOhgE25v/vvUKnM1fryMXbMCMXy3YyNZxs9jdQDo3WPJFN6K17xThXKp2E4yKRvSdZLNGZ/NfgLTiJOQc6rvE4RnBYwJeOK4lkZNYeY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WTjkhAl5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WTjkhAl5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A8445C2BCAF; Thu, 23 Apr 2026 19:44:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776973503; bh=ENC60U4eoLTeOFgHvSyl4mRh0gHFD8ZCM+8UztNm+Oc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=WTjkhAl5drIfu9apC/Pi9agzSVtP58XXpDt2+cIt9h3kL6pdH1FmRKQU8q4lE5mb/ hCR0Jxqd4pQYChGR9GdRdJDAoZyFicegVlKibLa0Lufvv7X8N0JEYqUrGI0oh7Vv/M 3oEdsdTEVdvpkpGLwXo8VQyyOxHEPzYnM/aTsFCYPIyouxcSwpu1GHz0uUwGJEWkuj iQ8omD6X26DJfCh4G4tx2nwQFQLflEQuYa9LlRrKm758y9dvJwkI7pjAZrffcRkPDV Ki8Zekn7Y9+qoDgsT/rDBXYUiYpaOMrmIzWirEsXPA0oabydG9O3thHtUWGRWVMTlr g14lLOI11hBYQ== Message-ID: <1bcf0c90-7aee-47b2-a58c-7932e6ad088a@kernel.org> Date: Thu, 23 Apr 2026 21:44:52 +0200 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 7.2 v9 2/2] x86/tlb: skip redundant sync IPIs for native TLB flush To: Dave Hansen , Lance Yang , akpm@linux-foundation.org Cc: peterz@infradead.org, dave.hansen@linux.intel.com, ypodemsk@redhat.com, hughd@google.com, will@kernel.org, aneesh.kumar@kernel.org, npiggin@gmail.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, arnd@arndb.de, ljs@kernel.org, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, shy828301@gmail.com, riel@surriel.com, jannh@google.com, jgross@suse.com, seanjc@google.com, pbonzini@redhat.com, boris.ostrovsky@oracle.com, virtualization@lists.linux.dev, kvm@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ioworker0@gmail.com References: <20260420030851.6735-1-lance.yang@linux.dev> <20260420030851.6735-3-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 4/23/26 19:56, Dave Hansen wrote: > On 4/19/26 20:08, Lance Yang wrote: >> - flush_tlb_mm_range(tlb->mm, start, end, stride_shift, tlb->freed_tables); >> + /* >> + * Treat unshared_tables just like freed_tables, such that lazy-TLB >> + * CPUs also receive IPIs during unsharing of page tables, allowing >> + * us to safely implement tlb_table_flush_implies_ipi_broadcast(). >> + */ >> + flush_tlb_mm_range(tlb->mm, start, end, stride_shift, >> + tlb->freed_tables || tlb->unshared_tables); >> } > > I've been staring at this trying to make sense of it for too long. > > Right now, flush_tlb_mm_range() literally has an argument named > "freed_tables" and "tlb->freed_tables" is passed there. That seems > totally sane. It's 100% straightforward to follow. > > But it makes zero logical sense to me to now mix "tlb->unshared_tables" > in there. Sure, what you _want_ is the freed_tables==1 behavior from > tlb->unshared_tables==1, and this obviously hacks that in there, but > it's not explained well enough and not maintainable like this. IOW, it's > still just hack. > > I think what's happened here is that info->freed_tables is being > modified from being strictly related to page table freeing, and moved > over to a bit which tells TLB flushing implementations whether they can > respect CPUs in lazy TLB mode. > > It's mentioned in the comment, but then ever reflected into the code. > > Shouldn't we be doing something like the attached patch? Look at how > that maps over to the flushing side, like in the hyperv code: > >> - bool do_lazy = !info->freed_tables; >> + bool do_lazy = !info->wake_lazy_cpus; >> >> trace_hyperv_mmu_flush_tlb_multi(cpus, info); >> >> @@ -198,7 +198,7 @@ static u64 hyperv_flush_tlb_others_ex(co >> >> flush->hv_vp_set.format = HV_GENERIC_SET_SPARSE_4K; >> nr_bank = cpumask_to_vpset_skip(&flush->hv_vp_set, cpus, >> - info->freed_tables ? NULL : cpu_is_lazy); >> + info->wake_lazy_cpus ? NULL : cpu_is_lazy); > > That even makes the hyperv code easier to read over what was there > before, IMNHO. > > Thoughts? Looks better! -- Cheers, David