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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id a124sm3518464wmh.39.2021.03.02.11.39.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Mar 2021 11:39:29 -0800 (PST) Subject: Re: [PATCH] KVM: SVM: Clear the CR4 register on reset To: Babu Moger Cc: wanpengli@tencent.com, kvm@vger.kernel.org, seanjc@google.com, joro@8bytes.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, vkuznets@redhat.com, tglx@linutronix.de, jmattson@google.com References: <161471109108.30811.6392805173629704166.stgit@bmoger-ubuntu> From: Paolo Bonzini Message-ID: <454cb7d4-9f50-42e1-6908-d659491ba140@redhat.com> Date: Tue, 2 Mar 2021 20:39:28 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: <161471109108.30811.6392805173629704166.stgit@bmoger-ubuntu> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/03/21 19:51, Babu Moger wrote: > This problem was reported on a SVM guest while executing kexec. > Kexec fails to load the new kernel when the PCID feature is enabled. > > When kexec starts loading the new kernel, it starts the process by > resetting the vCPU's and then bringing each vCPU online one by one. > The vCPU reset is supposed to reset all the register states before the > vCPUs are brought online. However, the CR4 register is not reset during > this process. If this register is already setup during the last boot, > all the flags can remain intact. The X86_CR4_PCIDE bit can only be > enabled in long mode. So, it must be enabled much later in SMP > initialization. Having the X86_CR4_PCIDE bit set during SMP boot can > cause a boot failures. > > Fix the issue by resetting the CR4 register in init_vmcb(). > > Signed-off-by: Babu Moger > --- > arch/x86/kvm/svm/svm.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c > index c636021b066b..baee91c1e936 100644 > --- a/arch/x86/kvm/svm/svm.c > +++ b/arch/x86/kvm/svm/svm.c > @@ -1200,6 +1200,7 @@ static void init_vmcb(struct vcpu_svm *svm) > init_sys_seg(&save->ldtr, SEG_TYPE_LDT); > init_sys_seg(&save->tr, SEG_TYPE_BUSY_TSS16); > > + svm_set_cr4(&svm->vcpu, 0); > svm_set_efer(&svm->vcpu, 0); > save->dr6 = 0xffff0ff0; > kvm_set_rflags(&svm->vcpu, X86_EFLAGS_FIXED); > Queued, thanks. Paolo