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X-CSE-ConnectionGUID: QEqy8aipRneghKDZWzbUgg== X-CSE-MsgGUID: 7E8Pg+JNQkCi+k4zI65MBA== X-IronPort-AV: E=McAfee;i="6700,10204,11363"; a="41273577" X-IronPort-AV: E=Sophos;i="6.14,220,1736841600"; d="scan'208";a="41273577" Received: from fmviesa004.fm.intel.com ([10.60.135.144]) by fmvoesa112.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2025 07:24:34 -0800 X-CSE-ConnectionGUID: mdKDqChQTJqGu5Eny0WrvA== X-CSE-MsgGUID: adTTfgKcQEaR1dxZeWjN9A== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.14,220,1736841600"; d="scan'208";a="123527461" Received: from kinlongk-desk.amr.corp.intel.com (HELO [10.125.109.94]) ([10.125.109.94]) by fmviesa004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 04 Mar 2025 07:24:33 -0800 Message-ID: Date: Tue, 4 Mar 2025 07:24:51 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v14 11/13] x86/mm: do targeted broadcast flushing from tlbbatch code To: Borislav Petkov Cc: Rik van Riel , x86@kernel.org, linux-kernel@vger.kernel.org, peterz@infradead.org, dave.hansen@linux.intel.com, zhengqi.arch@bytedance.com, nadav.amit@gmail.com, thomas.lendacky@amd.com, kernel-team@meta.com, linux-mm@kvack.org, akpm@linux-foundation.org, jackmanb@google.com, jannh@google.com, mhklinux@outlook.com, andrew.cooper3@citrix.com, Manali.Shukla@amd.com, mingo@kernel.org References: <20250226030129.530345-1-riel@surriel.com> <20250226030129.530345-12-riel@surriel.com> <20250303114618.GBZ8WWihMDjf-oy8P0@fat_crate.local> <7e1ca8c7-6f3e-44dc-9dd8-bd273a03a83e@intel.com> <20250304115207.GFZ8bpZ83u7L9x43Rq@fat_crate.local> From: Dave Hansen Content-Language: en-US Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 4854180026 X-Stat-Signature: m6snpdwp87978jjdzo3jcgytpz4ncduy X-HE-Tag: 1741101875-520409 X-HE-Meta: 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 yyI0X/li jpPkb3iOrsbNspHB253W+dOg8iRhbuFdSkHOmDtpkQaSZ5Eiun0dAtN91zZC5DZ4Ro2g9jm+/fZQyhSkE898i5lElu26g0WtgVGRUJ4m//EtKdr/HVL2J9eAMC6eKiS9olURVeqGZla0YHSxxfmROz4yYv3uLhfcA98htcZe2/qF/ljxNjU+zWbiqnaRu+fgE3QVQcwDeyAruvSkqh5JnU/+rtAAjeFxqWgfsxfp0OuQCuxTrCr6cdKSDoF3leyjGw0dSNxx8l6VB1D6kw1dXgzvPZQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/4/25 03:52, Borislav Petkov wrote: > On Mon, Mar 03, 2025 at 01:47:42PM -0800, Dave Hansen wrote: ... > IOW, this: > > /* Flush all mappings for a given PCID, not including globals. */ > static inline void __invlpgb_flush_single_pcid_nosync(unsigned long pcid) > { > __invlpgb(0, pcid, 0, 1, 0, INVLPGB_PCID); > cpu_set_tlbsync(true); > } > > Right? Yep, that works. Optimizing out the writes like the old code did is certainly a good thought. But I suspect the cacheline is hot the majority of the time. >>> static void broadcast_tlb_flush(struct flush_tlb_info *info) >>> { >>> bool pmd = info->stride_shift == PMD_SHIFT; >>> @@ -790,6 +821,8 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, >>> if (IS_ENABLED(CONFIG_PROVE_LOCKING)) >>> WARN_ON_ONCE(!irqs_disabled()); >>> >>> + tlbsync(); >> >> This one is in dire need of comments. > > Maybe this: > > diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c > index 08672350536f..b97249ffff1f 100644 > --- a/arch/x86/mm/tlb.c > +++ b/arch/x86/mm/tlb.c > @@ -822,6 +822,9 @@ void switch_mm_irqs_off(struct mm_struct *unused, struct mm_struct *next, > if (IS_ENABLED(CONFIG_PROVE_LOCKING)) > WARN_ON_ONCE(!irqs_disabled()); > > + /* > + * Finish any remote TLB flushes pending from this CPU: > + */ > tlbsync(); That's a prototypical "what" comment and not "why", though. It makes a lot of sense that any flushes that the old task did should complete before a new gets activated. But I honestly can't think of a _specific_ problem that it causes. I don't doubt that this does _some_ good, but I just don't know what good it does. ;)