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Thu, 22 Jul 2021 12:33:59 -0700 (PDT) Date: Thu, 22 Jul 2021 21:33:52 +0200 From: Marco Elver To: Quentin Perret Cc: Shameerali Kolothum Thodi , Will Deacon , "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" , Linuxarm , mark.rutland@arm.com Subject: Re: [PATCH v2 3/3] kvm/arm: Align the VMID allocation with the arm64 ASID one Message-ID: References: <20210616155606.2806-1-shameerali.kolothum.thodi@huawei.com> <20210616155606.2806-4-shameerali.kolothum.thodi@huawei.com> <20210721163138.GD11003@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.0.5 (2021-01-21) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 22, 2021 at 10:11AM +0100, Quentin Perret wrote: > On Thursday 22 Jul 2021 at 06:45:14 (+0000), Shameerali Kolothum Thodi wrote: > > > From: Will Deacon [mailto:will@kernel.org] > > > > diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > > index 4b60c0056c04..a02c4877a055 100644 > > > > --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > > +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c > > > > @@ -106,8 +106,7 @@ int kvm_host_prepare_stage2(void *mem_pgt_pool, > > > void *dev_pgt_pool) > > > > mmu->pgd_phys = __hyp_pa(host_kvm.pgt.pgd); > > > > mmu->arch = &host_kvm.arch; > > > > mmu->pgt = &host_kvm.pgt; > > > > - mmu->vmid.vmid_gen = 0; > > > > - mmu->vmid.vmid = 0; > > > > + atomic64_set(&mmu->vmid.id, 0); > > > > > > I think this is the first atomic64 use in the EL2 object, which may pull in > > > some fatal KCSAN instrumentation. Quentin, have you run into this before? > > > > > > Might be simple just to zero-initialise mmu for now, if it isn't already. > > > > I will check that. > > Yes I think what saves us here is that, AFAICT. arm64 doesn't support > KCSAN yet. But the day it does, this should fail to link (hopefully) > because of out-of-line calls into e.g. __kasan_check_write(). > > So yes, a simple zeroing here is probably preferable. Note: Do not worry about hypothetically breaking with sanitizers here -- whether it's KASAN or KCSAN, they both instrument atomics. In files that enable instrumentation but the atomic instrumentation should not be pulled in, use the arch_ variants, but this doesn't apply here because instrumentation shouldn't even be on. The indicator that when KCSAN is supported on arm64, the Makefile here just needs KCSAN_SANITIZE := n, is that all other instrumentation is also killed entirely: $ grep -E "(PROFILE|SANITIZE|INSTRUMENT)" arch/arm64/kvm/hyp/nvhe/Makefile GCOV_PROFILE := n KASAN_SANITIZE := n UBSAN_SANITIZE := n KCOV_INSTRUMENT := n KCSAN isn't supported on arm64 yet, and when it does, I believe Mark's arm64 KCSAN series should take care of things like this. Thanks, -- Marco