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X-CSE-ConnectionGUID: CgLLv0SZTU6GpQvs2SgkWQ== X-CSE-MsgGUID: m24X//KVRyOuOCOrrTuRXA== X-IronPort-AV: E=McAfee;i="6800,10657,11719"; a="73787446" X-IronPort-AV: E=Sophos;i="6.21,324,1763452800"; d="scan'208";a="73787446" Received: from fmviesa009.fm.intel.com ([10.60.135.149]) by fmvoesa108.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2026 09:59:07 -0800 X-CSE-ConnectionGUID: 4TQsiUvKR6SROeOWGs/bKg== X-CSE-MsgGUID: m6KG54ICSbu6tHecqNx0sQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.21,324,1763452800"; d="scan'208";a="214537504" Received: from aschende-mobl.amr.corp.intel.com (HELO [10.125.108.205]) ([10.125.108.205]) by fmviesa009-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2026 09:59:05 -0800 Message-ID: <7dc30fbf-17c0-47db-8457-24b531cd0071@intel.com> Date: Wed, 4 Mar 2026 09:59:11 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 2/2] x86/tlb: skip redundant sync IPIs for native TLB flush To: Lance Yang , akpm@linux-foundation.org Cc: 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, lorenzo.stoakes@oracle.com, 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: <20260304021046.18550-1-lance.yang@linux.dev> <20260304021046.18550-3-lance.yang@linux.dev> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 0179C1C000E X-Stat-Signature: yc5yxndscmj6hznq6eb5wnmoyyg8hbmd X-HE-Tag: 1772647147-246292 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/3/26 18:10, Lance Yang wrote: ... > + if (pv_ops.mmu.flush_tlb_multi == native_flush_tlb_multi && > + !cpu_feature_enabled(X86_FEATURE_INVLPGB)) { > + pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = true; > + static_branch_enable(&tlb_ipi_broadcast_key); > + } > +} ... > +#ifndef CONFIG_PARAVIRT > +void __init native_pv_tlb_init(void) > +{ > + /* > + * For non-PARAVIRT builds, check if native TLB flush sends real IPIs > + * (i.e., not using INVLPGB broadcast invalidation). > + */ > + if (!cpu_feature_enabled(X86_FEATURE_INVLPGB)) > + static_branch_enable(&tlb_ipi_broadcast_key); > +} > +#endif I really despise duplicated logic. The X86_FEATURE_INVLPGB check is small, but it is duplicated. You're also setting the static branch in a *bunch* of different places. Can this be arranged so that the PV code just tells the core code that it is compatible with flush_tlb_multi_implies_ipi_broadcast? void __init bool is_pv_ok(void) { /* This check is super sketchy an unexplained: */ if (pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast) return true; if (pv_ops.mmu.flush_tlb_multi != native_flush_tlb_multi) return false; pv_ops.mmu.flush_tlb_multi_implies_ipi_broadcast = true; return true; } void __init tlb_init(void) { if (!is_pv_ok()) return; if (cpu_feature_enabled(X86_FEATURE_INVLPGB)) return; static_branch_enable(&tlb_ipi_broadcast_key); } Isn't that like a billion times more readable? It has one X86_FEATURE_INVLPGB check and one static_branch_enable() point and no #ifdeffery other than defining a stub is_pv_ok(). BTW, why is there even an early return for the case where flush_tlb_multi_implies_ipi_broadcast is already set? Isn't this decision made once on the boot CPU and then never touched again? Do any PV instances actually set the bit?