From patchwork Thu Oct 5 09:50:10 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Mark Rutland X-Patchwork-Id: 13409946 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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 3DF81E8FDC3 for ; Thu, 5 Oct 2023 09:52:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=zhZ1NDzGfnd2H4PRsHAh5fo/7iYZw9wsBGN4Iv8LT8g=; b=Ryle+xJR0IQA20 0+tvfAkGQ0l6VUovUtCAmx9+vkxV1WKpCWuCUG0RQ3ysH+D0F+d0XfL703vUzPUFlGOl5veklymsb skPEdb0lXLrXCbOmQ8dn6nH2ztS4UDWvNu4Ex+Qf7bT7AtBNt8gWWvDKhnxmBfdrGiBUNy41apmrN H/dWfdkMqJ1NmRubflCdyA8LdEAx0d15wL+fCXUHZwGfkoME2KNoWZ847MLnEPX1Vj6Hx6cKqI63j bpjPGPEBjPzJ3/UiBz6L2rXbJSwoJ/0+QAtxTa6vM46FGnlQ5wIrqfy2DQfpwMyC13xmL8RkJoN4G Yd2kJHRUREB3G+KJS7pQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qoL1g-001oQo-0Z; Thu, 05 Oct 2023 09:52:12 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1qoL1S-001oE8-1d for linux-arm-kernel@lists.infradead.org; Thu, 05 Oct 2023 09:52:07 +0000 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 EFA651570; Thu, 5 Oct 2023 02:52:35 -0700 (PDT) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 17C993F5A1; Thu, 5 Oct 2023 02:51:54 -0700 (PDT) From: Mark Rutland To: linux-arm-kernel@lists.infradead.org Cc: ardb@kernel.org, bertrand.marquis@arm.com, boris.ostrovsky@oracle.com, broonie@kernel.org, catalin.marinas@arm.com, daniel.lezcano@linaro.org, james.morse@arm.com, jgross@suse.com, kristina.martsenko@arm.com, mark.rutland@arm.com, maz@kernel.org, oliver.upton@linux.dev, pcc@google.com, sstabellini@kernel.org, suzuki.poulose@arm.com, tglx@linutronix.de, vladimir.murzin@arm.com, will@kernel.org Subject: [PATCH v2 23/38] arm64: Avoid cpus_have_const_cap() for ARM64_HAS_RNG Date: Thu, 5 Oct 2023 10:50:10 +0100 Message-Id: <20231005095025.1872048-25-mark.rutland@arm.com> X-Mailer: git-send-email 2.30.2 In-Reply-To: <20231005095025.1872048-1-mark.rutland@arm.com> References: <20231005095025.1872048-1-mark.rutland@arm.com> MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20231005_025158_613809_C8094DBC X-CRM114-Status: GOOD ( 15.86 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org In __cpu_has_rng() we use cpus_have_const_cap() to check for ARM64_HAS_RNG, but this is not necessary and alternative_has_cap_*() would be preferable. For historical reasons, cpus_have_const_cap() is more complicated than it needs to be. Before cpucaps are finalized, it will perform a bitmap test of the system_cpucaps bitmap, and once cpucaps are finalized it will use an alternative branch. This used to be necessary to handle some race conditions in the window between cpucap detection and the subsequent patching of alternatives and static branches, where different branches could be out-of-sync with one another (or w.r.t. alternative sequences). Now that we use alternative branches instead of static branches, these are all patched atomically w.r.t. one another, and there are only a handful of cases that need special care in the window between cpucap detection and alternative patching. Due to the above, it would be nice to remove cpus_have_const_cap(), and migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(), or cpus_have_cap() depending on when their requirements. This will remove redundant instructions and improve code generation, and will make it easier to determine how each callsite will behave before, during, and after alternative patching. In the window between detecting the ARM64_HAS_RNG cpucap and patching alternative branches, nothing which calls __cpu_has_rng() can run, and hence it's not necessary to use cpus_have_const_cap(). This patch replaces the use of cpus_have_const_cap() with alternative_has_cap_unlikely(), which will avoid generating code to test the system_cpucaps bitmap and should be better for all subsequent calls at runtime. Signed-off-by: Mark Rutland Reviewed-by: Mark Brown Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Suzuki K Poulose Cc: Will Deacon --- arch/arm64/include/asm/archrandom.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/include/asm/archrandom.h b/arch/arm64/include/asm/archrandom.h index b0abc64f86b03..ecdb3cfcd0f8c 100644 --- a/arch/arm64/include/asm/archrandom.h +++ b/arch/arm64/include/asm/archrandom.h @@ -63,7 +63,7 @@ static __always_inline bool __cpu_has_rng(void) { if (unlikely(!system_capabilities_finalized() && !preemptible())) return this_cpu_has_cap(ARM64_HAS_RNG); - return cpus_have_const_cap(ARM64_HAS_RNG); + return alternative_has_cap_unlikely(ARM64_HAS_RNG); } static inline size_t __must_check arch_get_random_longs(unsigned long *v, size_t max_longs)