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

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Message-ID: <be33873f-ae4e-4db9-bca4-e83e8d4b39c3@redhat.com>
Date: Wed, 26 Feb 2025 19:38:21 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Sean Christopherson <seanjc@...gle.com>, 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>
Cc: 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>,
 Yan Zhao <yan.y.zhao@...el.com>,
 Rick P Edgecombe <rick.p.edgecombe@...el.com>,
 Kai Huang <kai.huang@...el.com>, Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH 0/7] KVM: x86: nVMX IRQ fix and VM teardown cleanups

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