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Tue, 14 Jul 2020 08:40:59 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 8831E305C22; Tue, 14 Jul 2020 10:40:57 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 7393128B91072; Tue, 14 Jul 2020 10:40:57 +0200 (CEST) Date: Tue, 14 Jul 2020 10:40:57 +0200 From: Peter Zijlstra To: ira.weiny@intel.com Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Andy Lutomirski , x86@kernel.org, Dave Hansen , Dan Williams , Vishal Verma , Andrew Morton , Fenghua Yu , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [RFC PATCH 11/15] memremap: Add zone device access protection Message-ID: <20200714084057.GP10769@hirez.programming.kicks-ass.net> References: <20200714070220.3500839-1-ira.weiny@intel.com> <20200714070220.3500839-12-ira.weiny@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200714070220.3500839-12-ira.weiny@intel.com> X-Rspamd-Queue-Id: 8D50A180C0609 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam02 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: On Tue, Jul 14, 2020 at 12:02:16AM -0700, ira.weiny@intel.com wrote: > +static pgprot_t dev_protection_enable_get(struct dev_pagemap *pgmap, pgprot_t prot) > +{ > + if (pgmap->flags & PGMAP_PROT_ENABLED && dev_page_pkey != PKEY_INVALID) { > + pgprotval_t val = pgprot_val(prot); > + > + mutex_lock(&dev_prot_enable_lock); > + dev_protection_enable++; > + /* Only enable the static branch 1 time */ > + if (dev_protection_enable == 1) > + static_branch_enable(&dev_protection_static_key); > + mutex_unlock(&dev_prot_enable_lock); > + > + prot = __pgprot(val | _PAGE_PKEY(dev_page_pkey)); > + } > + return prot; > +} > + > +static void dev_protection_enable_put(struct dev_pagemap *pgmap) > +{ > + if (pgmap->flags & PGMAP_PROT_ENABLED && dev_page_pkey != PKEY_INVALID) { > + mutex_lock(&dev_prot_enable_lock); > + dev_protection_enable--; > + if (dev_protection_enable == 0) > + static_branch_disable(&dev_protection_static_key); > + mutex_unlock(&dev_prot_enable_lock); > + } > +} That's an anti-pattern vs static_keys, I'm thinking you actually want static_key_slow_{inc,dec}() instead of {enable,disable}().