linux-kernel - Re: [PATCH 1/7] KVM: x86: Free vCPUs before freeing VM state

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Message-ID: <Z71072F7FMz5aq/Q@yzhao56-desk.sh.intel.com>
Date: Tue, 25 Feb 2025 15:44:47 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan
	<maddy@...ux.ibm.com>, Anup Patel <anup@...infault.org>, Paul Walmsley
	<paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou
	<aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda
	<imbrenda@...ux.ibm.com>, Paolo Bonzini <pbonzini@...hat.com>,
	<linux-arm-kernel@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
	<kvm@...r.kernel.org>, <loongarch@...ts.linux.dev>,
	<linux-mips@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<kvm-riscv@...ts.infradead.org>, <linux-riscv@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, Aaron Lewis <aaronlewis@...gle.com>, "Jim
 Mattson" <jmattson@...gle.com>, Rick P Edgecombe
	<rick.p.edgecombe@...el.com>, Kai Huang <kai.huang@...el.com>, Isaku Yamahata
	<isaku.yamahata@...el.com>
Subject: Re: [PATCH 1/7] KVM: x86: Free vCPUs before freeing VM state

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 58b82d6fd77c..045c61cc7e54 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -12890,11 +12890,11 @@ void kvm_arch_destroy_vm(struct kvm *kvm)
>  		mutex_unlock(&kvm->slots_lock);
>  	}
>  	kvm_unload_vcpu_mmus(kvm);
> +	kvm_destroy_vcpus(kvm);
>  	kvm_x86_call(vm_destroy)(kvm);
>  	kvm_free_msr_filter(srcu_dereference_check(kvm->arch.msr_filter, &kvm->srcu, 1));
>  	kvm_pic_destroy(kvm);
>  	kvm_ioapic_destroy(kvm);
> -	kvm_destroy_vcpus(kvm);
>  	kvfree(rcu_dereference_check(kvm->arch.apic_map, 1));
>  	kfree(srcu_dereference_check(kvm->arch.pmu_event_filter, &kvm->srcu, 1));
>  	kvm_mmu_uninit_vm(kvm);
After this change, now the sequence is that

1. kvm_arch_pre_destroy_vm()
2. kvm_arch_destroy_vm()
   2.1 kvm_destroy_vcpus()
   2.2 .vm_destroy hook
   2.3 kvm_mmu_uninit_vm() --> mirror root ref is 1 upon here. Zap the mirror
                               root and reclaim SETP page table pages.
   2.4 .vm_free hook

Since TDX needs to reclaim the TDR page after reclaiming all other pages, we
currently added a vm_free hook at 2.4, after 2.3.

Could we move kvm_mmu_uninit_vm() before the .vm_destroy hook and after
kvm_destroy_vcpus()?

Or move the .vm_destroy hook after kvm_mmu_uninit_vm(), e.g. after
kvm_page_track_cleanup()?

Otherwise, TDX still needs to introduce the .vm_free hook, which is invoked at
the end of kvm_arch_destroy_vm().