linux-kernel - Re: [PATCH 19/21] KVM: TDX: Add an ioctl to create initial guest memory

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Message-ID: <0feae675-3ccb-4d0e-b2cd-4477f9288058@redhat.com>
Date: Tue, 10 Sep 2024 12:13:49 +0200
From: Paolo Bonzini <pbonzini@...hat.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
 "Zhao, Yan Y" <yan.y.zhao@...el.com>
Cc: "seanjc@...gle.com" <seanjc@...gle.com>, "Huang, Kai"
 <kai.huang@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
 "dmatlack@...gle.com" <dmatlack@...gle.com>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "nik.borisov@...e.com" <nik.borisov@...e.com>
Subject: Re: [PATCH 19/21] KVM: TDX: Add an ioctl to create initial guest
 memory

On 9/6/24 18:30, Edgecombe, Rick P wrote:
> /*
>   * The case to care about here is a PTE getting zapped concurrently and
>   * this function erroneously thinking a page is mapped in the mirror EPT.
>   * The private mem zapping paths are already covered by other locks held
>   * here, but grab an mmu read_lock to not trigger the assert in
>   * kvm_tdp_mmu_gpa_is_mapped().
>   */
> 
> Yan, do you think it is sufficient?

If you're actually requiring that the other locks are sufficient, then 
there can be no ENOENT.

Maybe:

	/*
	 * The private mem cannot be zapped after kvm_tdp_map_page()
	 * because all paths are covered by slots_lock and the
	 * filemap invalidate lock.  Check that they are indeed enough.
	 */
	if (IS_ENABLED(CONFIG_KVM_PROVE_MMU)) {
		scoped_guard(read_lock, &kvm->mmu_lock) {
			if (KVM_BUG_ON(kvm,
				!kvm_tdp_mmu_gpa_is_mapped(vcpu, gpa)) {
				ret = -EIO;
				goto out;
			}
		}
	}

Paolo