Re: [PATCH v9 08/25] KVM: arm64: iommu: Add memory pool

[Mostafa Saleh <smostafa@google.com>]

On Thu, Oct 15, 2026 at 08:18:17PM +0000, sashiko-bot@kernel.org wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [High] kvm: fatal EL2 panic on IOMMU pool exhaustion
> --
> 
> commit 4301acf34cc06e2a4b1fab6b934f06ba07d48a9d
> Author: Mostafa Saleh <smostafa@google.com>
> Subject: KVM: arm64: iommu: Add memory pool
> 
> This patch reserves a memory pool for the IOMMU driver's shadow page tables
> early during boot based on the kvm-arm.iommu_pgt_mem command line parameter.
> The driver later allocates from and frees to this pool at runtime in
> protected KVM mode.
> 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/iommu.c b/arch/arm64/kvm/hyp/nvhe/iommu.c
> > --- a/arch/arm64/kvm/hyp/nvhe/iommu.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/iommu.c
> > @@ -115,6 +117,11 @@ int pkvm_iommu_init(void)
> >  	    !pkvm_iommu_ops->host_stage2_idmap)
> >  		return 0;
> >  
> > +	ret = hyp_pool_init(&iommu_pages_pool, hyp_virt_to_pfn(pool_base),
> > +			    nr_pages, 0);
> > +	if (ret)
> > +		return ret;
> > +
> >  	ret = pkvm_iommu_ops->init();
> >  	if (ret)
> >  		return ret;
> 
> [Severity: High]
> Will this trigger a fatal hypervisor panic if the host specifies an undersized
> pool?
> 
> The size of the newly introduced iommu_pages_pool is directly controlled by
> the host via the kvm-arm.iommu_pgt_mem command line parameter. If the
> host-provided pool size is too small, pkvm_iommu_snapshot_host_stage2()
> called immediately after this will exhaust the allocator and return -ENOMEM.
> 
> Because pkvm_iommu_init() wraps that call in a WARN_ON():
> 
> 	return WARN_ON(pkvm_iommu_snapshot_host_stage2());
> 
> and WARN_ON() at EL2 in nVHE/pKVM expands to a fatal BRK instruction, this
> exhaustion will crash the entire machine.
> 
> Could this be updated to propagate the error back to the host, instead of
> treating hyp_alloc_pages() failure as a fatal invariant violation?
> 

That is by design as explaind the same reply in v8:
https://lore.kernel.org/all/arKR23P92jOirpn-@google.com/

Thanks,
Mostafa

> -- 
> Sashiko AI review · https://sashiko.dev/#/patchset/20261015200903.2735565-1-smostafa@google.com?part=8