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Wed, 11 Aug 2021 09:06:10 +0000 Received: from szxga04-in.huawei.com ([45.249.212.190]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mDjtn-0066Ds-Vw for linux-arm-kernel@lists.infradead.org; Wed, 11 Aug 2021 08:47:45 +0000 Received: from dggems705-chm.china.huawei.com (unknown [172.30.72.59]) by szxga04-in.huawei.com (SkyGuard) with ESMTP id 4Gl3JD5Md4z18PRc; Wed, 11 Aug 2021 16:43:40 +0800 (CST) Received: from lhreml710-chm.china.huawei.com (10.201.108.61) by dggems705-chm.china.huawei.com (10.3.19.182) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2176.2; Wed, 11 Aug 2021 16:47:36 +0800 Received: from lhreml710-chm.china.huawei.com ([169.254.81.184]) by lhreml710-chm.china.huawei.com ([169.254.81.184]) with mapi id 15.01.2176.012; Wed, 11 Aug 2021 09:47:34 +0100 From: Shameerali Kolothum Thodi To: Will Deacon CC: "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" , "linux-kernel@vger.kernel.org" , "maz@kernel.org" , "catalin.marinas@arm.com" , "james.morse@arm.com" , "julien.thierry.kdev@gmail.com" , "suzuki.poulose@arm.com" , "jean-philippe@linaro.org" , "Alexandru.Elisei@arm.com" , "qperret@google.com" , Linuxarm Subject: RE: [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU schedule out Thread-Topic: [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU schedule out Thread-Index: AQHXhGar1JrryboKrU+7h+yU/0K2/6thny2AgAAaZCCAACXigIAMKHhQ Date: Wed, 11 Aug 2021 08:47:34 +0000 Message-ID: <99805c8519d14491a33f98592bf30a54@huawei.com> References: <20210729104009.382-1-shameerali.kolothum.thodi@huawei.com> <20210729104009.382-5-shameerali.kolothum.thodi@huawei.com> <20210803114034.GB30853@willie-the-truck> <20210803153036.GA31125@willie-the-truck> In-Reply-To: <20210803153036.GA31125@willie-the-truck> Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.47.26.133] MIME-Version: 1.0 X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210811_014744_476396_57B2EFF9 X-CRM114-Status: GOOD ( 19.31 ) 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: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Will, > -----Original Message----- > From: Will Deacon [mailto:will@kernel.org] > Sent: 03 August 2021 16:31 > To: Shameerali Kolothum Thodi > Cc: linux-arm-kernel@lists.infradead.org; kvmarm@lists.cs.columbia.edu; > linux-kernel@vger.kernel.org; maz@kernel.org; catalin.marinas@arm.com; > james.morse@arm.com; julien.thierry.kdev@gmail.com; > suzuki.poulose@arm.com; jean-philippe@linaro.org; > Alexandru.Elisei@arm.com; qperret@google.com; Linuxarm > > Subject: Re: [PATCH v3 4/4] KVM: arm64: Clear active_vmids on vCPU > schedule out [...] > I think we have to be really careful not to run into the "suspended > animation" problem described in ae120d9edfe9 ("ARM: 7767/1: let the ASID > allocator handle suspended animation") if we go down this road. > > Maybe something along the lines of: > > ROLLOVER > > * Take lock > * Inc generation > => This will force everybody down the slow path > * Record active VMIDs > * Broadcast TLBI > => Only active VMIDs can be dirty > => Reserve active VMIDs and mark as allocated > > VCPU SCHED IN > > * Set active VMID > * Check generation > * If mismatch then: > * Take lock > * Try to match a reserved VMID > * If no reserved VMID, allocate new > > VCPU SCHED OUT > > * Clear active VMID > > but I'm not daft enough to think I got it right first time. I think it > needs both implementing *and* modelling in TLA+ before we merge it! I attempted to implement the above algo as below. It seems to be working in both 16-bit vmid and 4-bit vmid test setup. Though I am not quite sure this Is exactly what you had in mind above and covers all corner cases. Please take a look and let me know. (The diff below is against this v3 series) Thanks, Shameer --->8<---- --- a/arch/arm64/kvm/vmid.c +++ b/arch/arm64/kvm/vmid.c @@ -43,7 +43,7 @@ static void flush_context(void) bitmap_clear(vmid_map, 0, NUM_USER_VMIDS); for_each_possible_cpu(cpu) { - vmid = atomic64_xchg_relaxed(&per_cpu(active_vmids, cpu), 0); + vmid = atomic64_read(&per_cpu(active_vmids, cpu)); /* Preserve reserved VMID */ if (vmid == 0) @@ -125,32 +125,17 @@ void kvm_arm_vmid_clear_active(void) void kvm_arm_vmid_update(struct kvm_vmid *kvm_vmid) { unsigned long flags; - u64 vmid, old_active_vmid; + u64 vmid; vmid = atomic64_read(&kvm_vmid->id); - - /* - * Please refer comments in check_and_switch_context() in - * arch/arm64/mm/context.c. - */ - old_active_vmid = atomic64_read(this_cpu_ptr(&active_vmids)); - if (old_active_vmid && vmid_gen_match(vmid) && - atomic64_cmpxchg_relaxed(this_cpu_ptr(&active_vmids), - old_active_vmid, vmid)) + if (vmid_gen_match(vmid)) { + atomic64_set(this_cpu_ptr(&active_vmids), vmid); return; - - raw_spin_lock_irqsave(&cpu_vmid_lock, flags); - - /* Check that our VMID belongs to the current generation. */ - vmid = atomic64_read(&kvm_vmid->id); - if (!vmid_gen_match(vmid)) { - vmid = new_vmid(kvm_vmid); - atomic64_set(&kvm_vmid->id, vmid); } - + raw_spin_lock_irqsave(&cpu_vmid_lock, flags); + vmid = new_vmid(kvm_vmid); + atomic64_set(&kvm_vmid->id, vmid); atomic64_set(this_cpu_ptr(&active_vmids), vmid); raw_spin_unlock_irqrestore(&cpu_vmid_lock, flags); } --->8<---- _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel