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a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1755596114; 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; bh=CZciOKLRsCJe6+CO8UzeOSGDAbt35EFDJxrVlWismP8=; b=rIIqjOUr/uMLvRWJzzaJzODHNspiWdYsNnkEQY5t83nZ/KlZOovyfHACnzkkMTIyeaEBU5 jU/l8p2GKC9S/jRrPeaalxztIhSGxMr+BMjiG+DCWRnae4wH/QAvqZKe+t5X5z2wd7/gQx l4mpesuGqraOORWz0eYB/IFFQS9xBKo= 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 3CE351BD0; Tue, 19 Aug 2025 02:35:04 -0700 (PDT) Received: from [10.57.56.191] (unknown [10.57.56.191]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4496B3F58B; Tue, 19 Aug 2025 02:35:03 -0700 (PDT) Message-ID: Date: Tue, 19 Aug 2025 11:35:01 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v5 13/18] mm: Map page tables with privileged pkey To: "Edgecombe, Rick P" , "linux-hardening@vger.kernel.org" Cc: "x86@kernel.org" , "maz@kernel.org" , "luto@kernel.org" , "mbland@motorola.com" , "willy@infradead.org" , "dave.hansen@linux.intel.com" , "david@redhat.com" , "rppt@kernel.org" , "joey.gouly@arm.com" , "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "pierre.langlois@arm.com" , "Weiny, Ira" , "vbabka@suse.cz" , "catalin.marinas@arm.com" , "jeffxu@chromium.org" , "linus.walleij@linaro.org" , "lorenzo.stoakes@oracle.com" , "kees@kernel.org" , "ryan.roberts@arm.com" , "tglx@linutronix.de" , "jannh@google.com" , "peterz@infradead.org" , "linux-arm-kernel@lists.infradead.org" , "will@kernel.org" , "qperret@google.com" , "linux-mm@kvack.org" , "broonie@kernel.org" References: <20250815085512.2182322-1-kevin.brodsky@arm.com> <20250815085512.2182322-14-kevin.brodsky@arm.com> <616011cf17f1654ac3ad8757f0f33425b3af1ddd.camel@intel.com> Content-Language: en-GB From: Kevin Brodsky In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspam-User: X-Rspamd-Queue-Id: A551E140008 X-Stat-Signature: qty68tfw7e41ffka1dg79xuk1zj3epiu X-HE-Tag: 1755596113-30096 X-HE-Meta: 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 Ltu+1KcY C6iTc4GzjW6NoWGHe1WNd9TTh1uli6ES6QxA5isNAk31daqW6Lno0KasLXR4ZFgygKmX9bkUt08XsHQ37LMtHIU5GDTQk0pilwDzOh7D6Cn+eE29Q+qcLspcMiyJ5yt4xpXOGO+2FJSgsBD+9lRRR8w/lgcLu8/l3VEl1WeDQE0UA9HePfPB1bA1Rp9K4H1VfZPZeD0eMyTIWwXzDo5hZ1IlqCqM5yf9nYBVNPAwQcYUSt1IYsIZUb/DrPg== 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 18/08/2025 19:01, Edgecombe, Rick P wrote: > On Mon, 2025-08-18 at 18:02 +0200, Kevin Brodsky wrote: >> The benchmarking results (see cover letter) don't seem to point to a >> major performance hit from setting the pkey on arm64 (worth noting that >> the linear mapping is PTE-mapped on arm64 today so no splitting should >> occur when setting the pkey). The overhead may well be substantially >> higher on x86. > It's surprising to me. The batching seems to be about switching the pkey, not > the conversion of the direct map. Correct, there is still a set_memory_pkey() for each PTP. > And with batching you measured a fork > benchmark actually sped up a tiny bit. Shouldn't it involve a pile of page table > allocations and so extra direct map work? It should indeed... > I don't know if it's possible the mock implementation skipped some set_memory() > work somehow? In fact you're absolutely right, in the mock implementation I benchmarked set_memory_pkey() is in fact a no-op :( This is because patch 6 gates set_memory_pkey() on system_supports_poe(), but the mock implementation [1] only modifies arch_kpkeys_enabled(). In other words the numbers in the cover letter correspond to the added pkey register switches, without touching the page tables. I am now re-running the benchmarks with set_memory_pkey() actually modifying the page tables. I'll reply to the cover letter with the updated numbers. - Kevin [1] https://gitlab.arm.com/linux-arm/linux-kb/-/commit/fd75b43abb354e84d06f3dfb05ce839e9fb13e08