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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id g12-20020a1709061e0c00b0079d7ec3b211sm73622ejj.150.2022.10.21.02.07.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 Oct 2022 02:07:55 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , Michael Kelley , Siddharth Chandrasekaran , Yuan Yao , Maxim Levitsky , linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v11 16/46] KVM: x86: hyper-v: Don't use sparse_set_to_vcpu_mask() in kvm_hv_send_ipi() In-Reply-To: References: <20221004123956.188909-1-vkuznets@redhat.com> <20221004123956.188909-17-vkuznets@redhat.com> Date: Fri, 21 Oct 2022 11:07:53 +0200 Message-ID: <87czalczo6.fsf@redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-hyperv@vger.kernel.org Sean Christopherson writes: > On Tue, Oct 04, 2022, Vitaly Kuznetsov wrote: ... >> >> - if (all_cpus) { >> - kvm_send_ipi_to_many(kvm, vector, NULL); >> - } else { >> - sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask, vcpu_mask); >> - >> - kvm_send_ipi_to_many(kvm, vector, vcpu_mask); >> - } >> + kvm_hv_send_ipi_to_many(kvm, vector, all_cpus ? NULL : sparse_banks, valid_bank_mask); > > Any objection to not using a ternary operator? > > if (all_cpus) > kvm_hv_send_ipi_to_many(kvm, vector, NULL, 0); > else > kvm_hv_send_ipi_to_many(kvm, vector, sparse_banks, valid_bank_mask); > Not at all, > Mostly because it's somewhat arbitrary that earlier code ensures valid_bank_mask > is set in the all_cpus=true case, e.g. arguably KVM doesn't need to do the var_cnt > sanity check in the all_cpus case: > > all_cpus = send_ipi_ex.vp_set.format == HV_GENERIC_SET_ALL; > if (all_cpus) > goto check_and_send_ipi; > > valid_bank_mask = send_ipi_ex.vp_set.valid_bank_mask; > if (hc->var_cnt != hweight64(valid_bank_mask)) > return HV_STATUS_INVALID_HYPERCALL_INPUT; > > if (!hc->var_cnt) > goto ret_success; > I think 'var_cnt' (== hweight64(valid_bank_mask)) has to be checked in 'all_cpus' case, especially in kvm_hv_flush_tlb(): the code which reads TLB flush entries will read them from the wrong offset (data_offset/ consumed_xmm_halves) otherwise. The problem is less severe in kvm_hv_send_ipi() as there's no data after CPU banks. At the bare minimum, "KVM: x86: hyper-v: Handle HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently" patch from this series will have to be adjusted. I *think* mandating var_cnt==0 in 'all_cpus' is OK but I don't recall such requirement from TLFS, maybe it's safer to just adjust 'data_offset'/'consumed_xmm_halves' even in 'all_cpus' case. Let me do some tests... -- Vitaly