Re: [PATCH 2/4] KVM: x86/mmu: Harden "map private PFN" against unexpected root invalidation

"Edgecombe, Rick P" <[email protected]> Fri, 7 Aug 2026 20:26:35 +0000

Newsgroups	org.kernel.vger.kvm,org.kernel.vger.linux-kernel
Message-ID	<[email protected]>

On Thu, 2026-08-06 at 14:40 -0700, Sean Christopherson wrote:
> @@ -5199,10 +5195,21 @@ int kvm_tdp_mmu_map_private_pfn(struct kvm_vcpu *vcpu, gfn_t gfn, kvm_pfn_t pfn)
>  		if (kvm_test_request(KVM_REQ_VM_DEAD, vcpu))
>  			return -EIO;
>  
> +		r = kvm_mmu_reload(vcpu);
> +		if (r)
> +			return r;
> +
>  		cond_resched();
>  
>  		guard(read_lock)(&kvm->mmu_lock);
>  
> +		/*
> +		 * Because slots_lock is held, it should be impossible for roots
> +		 * to be invalidated after the initial MMU reload.  WARN, but
> +		 * continue and re-reload the MMU to try and keep the VM alive.
> +		 */

It might be a little confusing when no MMU reload follows the comment. Maybe
mention that the MMU reload is above? Either way ok to me.

> +		WARN_ON_ONCE(kvm_test_request(KVM_REQ_MMU_FREE_OBSOLETE_ROOTS, vcpu));
> +
>  		r = kvm_tdp_mmu_map(vcpu, &fault);