From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id C32F3FB44A8 for ; Fri, 24 Apr 2026 05:03:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B897A6B0005; Fri, 24 Apr 2026 01:03:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B3B986B008A; Fri, 24 Apr 2026 01:03:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A29276B008C; Fri, 24 Apr 2026 01:03:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 8DCAD6B0005 for ; Fri, 24 Apr 2026 01:03:56 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01b-stub [10.200.18.250]) by unirelay03.hostedemail.com (Postfix) with ESMTP id E613EA06F3 for ; Fri, 24 Apr 2026 05:03:55 +0000 (UTC) X-FDA: 84692257230.23.3407BD0 Received: from out-176.mta1.migadu.com (out-176.mta1.migadu.com [95.215.58.176]) by imf19.hostedemail.com (Postfix) with ESMTP id EB9911A0011 for ; Fri, 24 Apr 2026 05:03:53 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=k6w7+Mgc; spf=pass (imf19.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1777007034; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=rF/14iOG/TKWQJ1iA5emqkLbN1JUZtyc7urLxXkKtYs=; b=dtr19nVgzoZxCw/CB/6JFQWuzZ8ZTm1TO2fkE6kze3A47CHEIEPYQf+6FB29XBRCgKdEJw ayKVFTiEPUqIs1kzcNQzMNT1x2N8TMT0H9bCebUdLIqbF/8JwCZSwlP5Ft7lPwW8WqUpiW WE9yAnHr4AC5GzDHCB20PdglOS/OoPo= ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=k6w7+Mgc; spf=pass (imf19.hostedemail.com: domain of lance.yang@linux.dev designates 95.215.58.176 as permitted sender) smtp.mailfrom=lance.yang@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1777007034; a=rsa-sha256; cv=none; b=4P9ltjOVsX0xrDa7dhLjHSENOLmONv38Avp7cVsFwTW/aG4seTb37JaeZ+pHJ2Fg+69Ag1 sAtSSl6bkHv2EXfMT269pQtc5rtD44EHRNxzliFWqC6+FDbCAv0bO691vQqj3jhpSi6Uho DlqHMOiu8jQHmj40OWK3CzgXjol9jlo= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1777007031; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rF/14iOG/TKWQJ1iA5emqkLbN1JUZtyc7urLxXkKtYs=; b=k6w7+MgcqYIlU+lFz2OOnnJETtGqStoZm15MrlwZJlFr80pOyWH6gZ6d2zM2guk98Kx4hw tXCLb6gF/s7OF6Yz18Pc0TSuybZ8lAg9MR+ILu0Icc1wm4wkNrZjQ12wjGjJGxTsyLLXJc mGIvQmB9tRHJGZ2PRed7SjpDnA1qOfM= From: Lance Yang To: dave.hansen@intel.com Cc: lance.yang@linux.dev, akpm@linux-foundation.org, peterz@infradead.org, david@kernel.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 Subject: Re: [PATCH 7.2 v9 2/2] x86/tlb: skip redundant sync IPIs for native TLB flush Date: Fri, 24 Apr 2026 13:03:29 +0800 Message-Id: <20260424050329.96623-1-lance.yang@linux.dev> In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: f96ooibhcym13yji7rmkfizewhpprs9b X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EB9911A0011 X-HE-Tag: 1777007033-794619 X-HE-Meta: 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 k+5De8Io 2hmnoz6apo7z1Ht2zkUkP/JB4gWnrvQi87FJhmepb3uXrxFssko7+a77a1mZbLUbSJ6mNq/K+jOhK9SkxptbWsOzcCb9pxzje/jhxoVpjjMv0N4UInsUjOzYJC0OYlA46btSXz7hge8hSV/Lhyq361jOwaRknkqFI4q4xdlSdEF45BPSvGRK6oojNnGD1UrNLhWgVsFgsSQpgBh86U77KRE+EFA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Dave, On Thu, Apr 23, 2026 at 10:56:03AM -0700, 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: Cool, thanks! I was trying to keep the change small by passing unshared_tables through the exsiting freed_tables argument, but that made the code a bit harder to follow ... > >> - 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? [...] Yeah, renaming the flush_tlb_info bit to wake_lazy_cpus reads much better. Will fold this into v10, Thanks for spelling it out! Lance