linux-kernel - Re: [PATCH 1/2] KVM: VMX: avoid running vmx_handle_exit

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Date:   Mon, 6 Sep 2021 12:09:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Jim Mattson <jmattson@...gle.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        "open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" 
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] KVM: VMX: avoid running vmx_handle_exit_irqoff in
 case of emulation

On 26/08/21 18:01, Sean Christopherson wrote:
>> +	if (vmx->emulation_required)
>> +		return;
> Rather than play whack-a-mole with flows consuming stale state, I'd much prefer
> to synthesize a VM-Exit(INVALID_GUEST_STATE).  Alternatively, just skip ->run()
> entirely by adding hooks in vcpu_enter_guest(), but that's a much larger change
> and probably not worth the risk at this juncture.

I'm going with Maxim's patch for now (and for stable kernels especially)
but I like the


+       if (unlikely(static_call(kvm_x86_emulation_required)(vcpu)))
+               return static_call(kvm_x86_emulate_invalid_guest_state)(vcpu);
+

idea.  I'll put a Fixes for 95b5a48c4f2b ("KVM: VMX: Handle NMIs, #MCs and
async #PFs in common irqs-disabled fn", Linux 5.3).

Paolo