linux-kernel - Re: [PATCH v5 7/8] KVM: VMX: Update PID-pointer table entry when APIC ID is changed

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Date:   Wed, 5 Jan 2022 13:13:46 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Zeng Guang <guang.zeng@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Kim Phillips <kim.phillips@....com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Jethro Beekman <jethro@...tanix.com>,
        Kai Huang <kai.huang@...el.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Robert Hu <robert.hu@...el.com>, Gao Chao <chao.gao@...el.com>
Subject: Re: [PATCH v5 7/8] KVM: VMX: Update PID-pointer table entry when APIC
 ID is changed

On 12/31/21 8:28 AM, Zeng Guang wrote:
> In xAPIC mode, guest is allowed to modify APIC ID at runtime.
> If IPI virtualization is enabled, corresponding entry in
> PID-pointer table need change accordingly.
> 
> Signed-off-by: Zeng Guang <guang.zeng@...el.com>
> ---
>   arch/x86/include/asm/kvm_host.h |  1 +
>   arch/x86/kvm/lapic.c            |  7 +++++--
>   arch/x86/kvm/vmx/vmx.c          | 12 ++++++++++++
>   3 files changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 2164b9f4c7b0..753bf2a7cebc 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1493,6 +1493,7 @@ struct kvm_x86_ops {
>   	int (*complete_emulated_msr)(struct kvm_vcpu *vcpu, int err);
>   
>   	void (*vcpu_deliver_sipi_vector)(struct kvm_vcpu *vcpu, u8 vector);
> +	void (*update_ipiv_pid_entry)(struct kvm_vcpu *vcpu, u8 old_id, u8 new_id);
>   };
>   
>   struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
> index 3ce7142ba00e..83c2c7594bcd 100644
> --- a/arch/x86/kvm/lapic.c
> +++ b/arch/x86/kvm/lapic.c
> @@ -2007,9 +2007,12 @@ int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
>   
>   	switch (reg) {
>   	case APIC_ID:		/* Local APIC ID */
> -		if (!apic_x2apic_mode(apic))
> +		if (!apic_x2apic_mode(apic)) {
> +			u8 old_id = kvm_lapic_get_reg(apic, APIC_ID) >> 24;
> +
>   			kvm_apic_set_xapic_id(apic, val >> 24);
> -		else
> +			kvm_x86_ops.update_ipiv_pid_entry(apic->vcpu, old_id, val >> 24);

Won't this blow up on AMD since there is no corresponding SVM op?

Thanks,
Tom

> +		} else
>   			ret = 1;
>   		break;
>   
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 2e65464d6dee..f21ce15c5eb8 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -7633,6 +7633,17 @@ static void vmx_vm_destroy(struct kvm *kvm)
>   		free_pages((unsigned long)kvm_vmx->pid_table, MAX_PID_TABLE_ORDER);
>   }
>   
> +static void vmx_update_ipiv_pid_entry(struct kvm_vcpu *vcpu, u8 old_id, u8 new_id)
> +{
> +	if (enable_ipiv && kvm_vcpu_apicv_active(vcpu)) {
> +		u64 *pid_table = to_kvm_vmx(vcpu->kvm)->pid_table;
> +
> +		WRITE_ONCE(pid_table[old_id], 0);
> +		WRITE_ONCE(pid_table[new_id], __pa(&to_vmx(vcpu)->pi_desc) |
> +				PID_TABLE_ENTRY_VALID);
> +	}
> +}
> +
>   static struct kvm_x86_ops vmx_x86_ops __initdata = {
>   	.name = "kvm_intel",
>   
> @@ -7770,6 +7781,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
>   	.complete_emulated_msr = kvm_complete_insn_gp,
>   
>   	.vcpu_deliver_sipi_vector = kvm_vcpu_deliver_sipi_vector,
> +	.update_ipiv_pid_entry = vmx_update_ipiv_pid_entry,
>   };
>   
>   static __init void vmx_setup_user_return_msrs(void)
>