From: Paolo Bonzini <pbonzini@redhat.com>
To: Babu Moger <babu.moger@amd.com>
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
Subject: Re: [PATCH] KVM: SVM: Clear the CR4 register on reset
Date: Tue, 2 Mar 2021 20:39:28 +0100 [thread overview]
Message-ID: <454cb7d4-9f50-42e1-6908-d659491ba140@redhat.com> (raw)
In-Reply-To: <161471109108.30811.6392805173629704166.stgit@bmoger-ubuntu>
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 <babu.moger@amd.com>
> ---
> 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
prev parent reply other threads:[~2021-03-02 22:37 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-02 18:51 [PATCH] KVM: SVM: Clear the CR4 register on reset Babu Moger
2021-03-02 19:20 ` Sean Christopherson
2021-03-02 19:29 ` Babu Moger
2021-03-02 19:39 ` Paolo Bonzini [this message]
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