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[82.81.161.50]) by smtp.gmail.com with ESMTPSA id z9-20020a05622a028900b003422c7ccbc5sm12259809qtw.59.2022.08.10.07.47.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 10 Aug 2022 07:47:09 -0700 (PDT) Message-ID: <11df1501c60809e5d83e2591fb43a3b660afaef4.camel@redhat.com> Subject: Re: [PATCH RFC v1 2/2] i386: reorder kvm_put_sregs2() and kvm_put_nested_state() when vCPU is reset From: Maxim Levitsky To: Vitaly Kuznetsov , qemu-devel@nongnu.org, Paolo Bonzini Cc: Sean Christopherson Date: Wed, 10 Aug 2022 17:47:06 +0300 In-Reply-To: <20220810140007.1036293-3-vkuznets@redhat.com> References: <20220810140007.1036293-1-vkuznets@redhat.com> <20220810140007.1036293-3-vkuznets@redhat.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.40.4 (3.40.4-5.fc34) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=mlevitsk@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, 2022-08-10 at 16:00 +0200, Vitaly Kuznetsov wrote: > Setting nested state upon migration needs to happen after kvm_put_sregs2() > to e.g. have EFER.SVME set. This, however, doesn't work for vCPU reset: > when vCPU is in VMX root operation, certain CR bits are locked and > kvm_put_sregs2() may fail. As nested state is fully cleaned up upon > vCPU reset (kvm_arch_reset_vcpu() -> kvm_init_nested_state()), calling > kvm_put_nested_state() before kvm_put_sregs2() is OK, this will ensure > that vCPU is *not* in VMX root opertaion. > > Signed-off-by: Vitaly Kuznetsov > --- >  target/i386/kvm/kvm.c | 20 ++++++++++++++++++-- >  1 file changed, 18 insertions(+), 2 deletions(-) > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index 4f8dacc1d4b5..73e3880fa57b 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -4529,18 +4529,34 @@ int kvm_arch_put_registers(CPUState *cpu, int level) >   >      assert(cpu_is_stopped(cpu) || qemu_cpu_is_self(cpu)); >   > -    /* must be before kvm_put_nested_state so that EFER.SVME is set */ > +    /* > +     * When resetting a vCPU, make sure to reset nested state first to > +     * e.g clear VMXON state and unlock certain CR4 bits. > +     */ > +    if (level == KVM_PUT_RESET_STATE) { > +        ret = kvm_put_nested_state(x86_cpu); > +        if (ret < 0) { > +            return ret; > +        } I should have mentioned this, I actually already debugged the same issue while trying to reproduce the smm int window bug. 100% my fault. I also share the same feeling that this might be yet another 'whack a mole' and break somewhere else, but overall it does make sense. Reviewed-by: Maxim Levitsky Best regards, Maxim Levitsky > +    } > + >      ret = has_sregs2 ? kvm_put_sregs2(x86_cpu) : kvm_put_sregs(x86_cpu); >      if (ret < 0) { >          return ret; >      } >   > -    if (level >= KVM_PUT_RESET_STATE) { > +    /* > +     * When putting full CPU state, kvm_put_nested_state() must happen after > +     * kvm_put_sregs{,2} so that e.g. EFER.SVME is already set. > +     */ > +    if (level == KVM_PUT_FULL_STATE) { >          ret = kvm_put_nested_state(x86_cpu); >          if (ret < 0) { >              return ret; >          } > +    } >   > +    if (level >= KVM_PUT_RESET_STATE) { >          ret = kvm_put_msr_feature_control(x86_cpu); >          if (ret < 0) { >              return ret;