linux-kernel - Re: [PATCH v2 0/5] KVM: x86/mmu: Don't synthesize triple fault on bad root

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Date:   Thu, 17 Aug 2023 17:12:00 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        Reima Ishii <ishiir@...cc.u-tokyo.ac.jp>
Subject: Re: [PATCH v2 0/5] KVM: x86/mmu: Don't synthesize triple fault on bad root

On Fri, 28 Jul 2023 17:51:55 -0700, Sean Christopherson wrote:
> Rework the handling of !visible guest root gfns to wait until the guest
> actually tries to access memory before synthesizing a fault.  KVM currently
> just immediately synthesizes triple fault, which causes problems for nVMX
> and nSVM as immediately injecting a fault causes KVM to try and forward the
> fault to L1 (as a VM-Exit) before completing nested VM-Enter, e.g. if L1
> runs L2 with a "bad" nested TDP root.
> 
> [...]

With some trepidation that I'm overlooking something, applied to kvm-x86 mmu.
Patches 1-4 are worthwhile on their own, so even if the actual fix is wildly
broken somehow and needs to be reverted, it'll just be that one commit that
gets nuked.

[1/5] KVM: x86/mmu: Add helper to convert root hpa to shadow page
      https://github.com/kvm-x86/linux/commit/732f57612d5c
[2/5] KVM: x86/mmu: Harden new PGD against roots without shadow pages
      https://github.com/kvm-x86/linux/commit/9e3f832edfca
[3/5] KVM: x86/mmu: Harden TDP MMU iteration against root w/o shadow page
      https://github.com/kvm-x86/linux/commit/004c297c327f
[4/5] KVM: x86/mmu: Disallow guest from using !visible slots for page tables
      https://github.com/kvm-x86/linux/commit/81d4621b7d9f
[5/5] KVM: x86/mmu: Use dummy root, backed by zero page, for !visible guest roots
      https://github.com/kvm-x86/linux/commit/a328a359d99b

--
https://github.com/kvm-x86/linux/tree/next
https://github.com/kvm-x86/linux/tree/fixes