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14 Feb 2019 09:42:24 -0800 Subject: Re: [RFC PATCH v8 13/14] xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) To: Khalid Aziz , juergh@gmail.com, tycho@tycho.ws, jsteckli@amazon.de, ak@linux.intel.com, torvalds@linux-foundation.org, liran.alon@oracle.com, keescook@google.com, akpm@linux-foundation.org, mhocko@suse.com, catalin.marinas@arm.com, will.deacon@arm.com, jmorris@namei.org, konrad.wilk@oracle.com Cc: deepa.srinivasan@oracle.com, chris.hyser@oracle.com, tyhicks@canonical.com, dwmw@amazon.co.uk, andrew.cooper3@citrix.com, jcm@redhat.com, boris.ostrovsky@oracle.com, kanth.ghatraju@oracle.com, oao.m.martins@oracle.com, jmattson@google.com, pradeep.vincent@oracle.com, john.haxby@oracle.com, tglx@linutronix.de, kirill.shutemov@linux.intel.com, hch@lst.de, steven.sistare@oracle.com, labbott@redhat.com, luto@kernel.org, peterz@infradead.org, kernel-hardening@lists.openwall.com, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org References: <98134cb73e911b2f0b59ffb76243a7777963d218.1550088114.git.khalid.aziz@oracle.com> From: Dave Hansen Openpgp: preference=signencrypt Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <98134cb73e911b2f0b59ffb76243a7777963d218.1550088114.git.khalid.aziz@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit 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: > #endif > + > + /* If there is a pending TLB flush for this CPU due to XPFO > + * flush, do it now. > + */ Don't forget CodingStyle in all this, please. > + if (cpumask_test_and_clear_cpu(cpu, &pending_xpfo_flush)) { > + count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED); > + __flush_tlb_all(); > + } This seems to exist in parallel with all of the cpu_tlbstate infrastructure. Shouldn't it go in there? Also, if we're doing full flushes like this, it seems a bit wasteful to then go and do later things like invalidate_user_asid() when we *know* that the asid would have been flushed by this operation. I'm pretty sure this isn't the only __flush_tlb_all() callsite that does this, so it's not really criticism of this patch specifically. It's more of a structural issue. > +void xpfo_flush_tlb_kernel_range(unsigned long start, unsigned long end) > +{ This is a bit lightly commented. Please give this some good descriptions about the logic behind the implementation and the tradeoffs that are in play. This is doing a local flush, but deferring the flushes on all other processors, right? Can you explain the logic behind that in a comment here, please? This also has to be called with preemption disabled, right? > + struct cpumask tmp_mask; > + > + /* Balance as user space task's flush, a bit conservative */ > + if (end == TLB_FLUSH_ALL || > + (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) { > + do_flush_tlb_all(NULL); > + } else { > + struct flush_tlb_info info; > + > + info.start = start; > + info.end = end; > + do_kernel_range_flush(&info); > + } > + cpumask_setall(&tmp_mask); > + cpumask_clear_cpu(smp_processor_id(), &tmp_mask); > + cpumask_or(&pending_xpfo_flush, &pending_xpfo_flush, &tmp_mask); > +} Fun. cpumask_setall() is non-atomic while cpumask_clear_cpu() and cpumask_or() *are* atomic. The cpumask_clear_cpu() is operating on thread-local storage and doesn't need to be atomic. Please make it __cpumask_clear_cpu().