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Date: Fri, 21 Oct 2022 14:41:19 +0200 From: Vitaly Kuznetsov <vkuznets@...hat.com> To: Sean Christopherson <seanjc@...gle.com> Cc: kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Michael Kelley <mikelley@...rosoft.com>, Siddharth Chandrasekaran <sidcha@...zon.de>, Yuan Yao <yuan.yao@...ux.intel.com>, Maxim Levitsky <mlevitsk@...hat.com>, linux-hyperv@...r.kernel.org, linux-kernel@...r.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() Vitaly Kuznetsov <vkuznets@...hat.com> writes: > Sean Christopherson <seanjc@...gle.com> 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... "We can neither confirm nor deny the existence of the problem". Windows guests seem to be smart enough to avoid using *_EX hypercalls altogether for "all cpus" case (as non-ex versions are good enough). Let's keep allowing non-zero var_cnt for 'all cpus' case for now and think about hardening it later... -- Vitaly
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