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Wed, 08 Jul 2026 22:45:33 -0700 (PDT) Received: from [10.42.12.77] ([116.128.244.169]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ccc99cc5aasm38156905ad.0.2026.07.08.22.45.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 08 Jul 2026 22:45:32 -0700 (PDT) Message-ID: Date: Thu, 9 Jul 2026 13:45:23 +0800 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: leixiang Subject: Re: [PATCH] KVM: Nullify irqfd->producer when add_producer() fails To: Sean Christopherson Cc: stable@vger.kernel.org, Madhavan Srinivasan , Nicholas Piggin , Michael Ellerman , "Christophe Leroy (CS GROUP)" , Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Mackerras , Suresh Warrier , linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, leixiang References: <1782119051448443.14545.seg@mailgw.kylinos.cn> Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 7/9/26 00:40, Sean Christopherson wrote: > On Mon, Jun 22, 2026, leixiang wrote: >> The x86 and powerpc add_producer() callbacks set irqfd->producer before the >> fallible setup and never clear it on error. The bypass manager doesn't >> register a producer whose add_producer() failed -- producer->eventfd is >> left NULL, so the later unregister early-returns and del_producer() is >> never called -- so nothing ever drops the pointer. >> >> For VFIO PCI the producer is embedded in struct vfio_pci_irq_ctx and freed >> when the vector is disabled, after which a routing update dereferences the >> dangling pointer via kvm_arch_update_irqfd_routing(). >> >> Nullify irqfd->producer on the error paths. >> >> Fixes: 77e1b8332d1d ("KVM: x86: Decouple device assignment from IRQ bypass") >> Fixes: c57875f5f9be ("KVM: PPC: Book3S HV: Enable IRQ bypass") >> Cc: stable@vger.kernel.org >> Signed-off-by: leixiang > > Please post the PPC patch as a separate patch. x86 and PPC are separate maintainer > domains and the backports will likely need to go to different LTS kernels. > > I'll grab/extract the x86 change from here (and I'll massage the changelog as > appropriate). Thank you for the review and guidance. I will submit a separate PPC patch. >> --- >> arch/powerpc/kvm/book3s_hv.c | 4 +++- >> arch/x86/kvm/irq.c | 4 +++- >> 2 files changed, 6 insertions(+), 2 deletions(-) >> >> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c >> index 61dbeea317f3..14919b76fb32 100644 >> --- a/arch/powerpc/kvm/book3s_hv.c >> +++ b/arch/powerpc/kvm/book3s_hv.c >> @@ -6114,9 +6114,11 @@ static int kvmppc_irq_bypass_add_producer_hv(struct irq_bypass_consumer *cons, >> irqfd->producer = prod; >> >> ret = kvmppc_set_passthru_irq(irqfd->kvm, prod->irq, irqfd->gsi); >> - if (ret) >> + if (ret) { >> pr_info("kvmppc_set_passthru_irq (irq %d, gsi %d) fails: %d\n", >> prod->irq, irqfd->gsi, ret); >> + irqfd->producer = NULL; >> + } > > Unlike x86, AFAICT there's no need to set irqfd->producer before configuring > the passthru/bypass stuff. So I think that fix could be this? > > diff --git arch/powerpc/kvm/book3s_hv.c arch/powerpc/kvm/book3s_hv.c > index 61dbeea317f3..ff7b25629125 100644 > --- arch/powerpc/kvm/book3s_hv.c > +++ arch/powerpc/kvm/book3s_hv.c > @@ -6111,12 +6111,12 @@ static int kvmppc_irq_bypass_add_producer_hv(struct irq_bypass_consumer *cons, > struct kvm_kernel_irqfd *irqfd = > container_of(cons, struct kvm_kernel_irqfd, consumer); > > - irqfd->producer = prod; > - > ret = kvmppc_set_passthru_irq(irqfd->kvm, prod->irq, irqfd->gsi); > if (ret) > pr_info("kvmppc_set_passthru_irq (irq %d, gsi %d) fails: %d\n", > prod->irq, irqfd->gsi, ret); > + else > + irqfd->producer = prod; > > return ret; > } Agreed. Your approach is cleaner.