Re: [PATCH 0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups

From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>,
	Marc Zyngier <maz@kernel.org>,
	Oliver Upton <oliver.upton@linux.dev>,
	Tianrui Zhao <zhaotianrui@loongson.cn>,
	Bibo Mao <maobibo@loongson.cn>,
	Huacai Chen <chenhuacai@kernel.org>,
	Madhavan Srinivasan <maddy@linux.ibm.com>,
	Anup Patel <anup@brainfault.org>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Christian Borntraeger <borntraeger@linux.ibm.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev,
	kvm@vger.kernel.org, loongarch@lists.linux.dev,
	linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
	kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, Aaron Lewis <aaronlewis@google.com>,
	Jim Mattson <jmattson@google.com>,
	Yan Zhao <yan.y.zhao@intel.com>,
	Rick P Edgecombe <rick.p.edgecombe@intel.com>,
	Kai Huang <kai.huang@intel.com>,
	Isaku Yamahata <isaku.yamahata@intel.com>
Subject: Re: [PATCH 0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups
Date: Wed, 26 Feb 2025 19:38:21 +0100	[thread overview]
Message-ID: <be33873f-ae4e-4db9-bca4-e83e8d4b39c3@redhat.com> (raw)
In-Reply-To: <20250224235542.2562848-1-seanjc@google.com>

On 2/25/25 00:55, Sean Christopherson wrote:
> This was _supposed_ to be a tiny one-off patch to fix a nVMX bug where KVM
> fails to detect that, after nested VM-Exit, L1 has a pending IRQ (or NMI).
> But because x86's nested teardown flows are garbage (KVM simply forces a
> nested VM-Exit to put the vCPU back into L1), that simple fix snowballed.
> 
> The immediate issue is that checking for a pending interrupt accesses the
> legacy PIC, and x86's kvm_arch_destroy_vm() currently frees the PIC before
> destroying vCPUs, i.e. checking for IRQs during the forced nested VM-Exit
> results in a NULL pointer deref (or use-after-free if KVM didn't nullify
> the PIC pointer).  That's patch 1.
> 
> Patch 2 is the original nVMX fix.
> 
> The remaining patches attempt to bring a bit of sanity to x86's VM
> teardown code, which has accumulated a lot of cruft over the years.  E.g.
> KVM currently unloads each vCPU's MMUs in a separate operation from
> destroying vCPUs, all because when guest SMP support was added, KVM had a
> kludgy MMU teardown flow that broken when a VM had more than one 1 vCPU.
> And that oddity lived on, for 18 years...

Queued patches 1 and 2 to kvm/master, and everything to kvm/queue 
(pending a little more testing and the related TDX change).

Paolo

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