linux-kernel - Re: [PATCH v2] KVM: X86: Explicitly set the 'fault.async_page_fault' value in kvm_fixup_and_inject_pf

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Message-ID: <Ytb/le8ymDSyx8oJ@google.com>
Date:   Tue, 19 Jul 2022 19:01:41 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yu Zhang <yu.c.zhang@...ux.intel.com>
Cc:     pbonzini@...hat.com, vkuznets@...hat.com, jmattson@...gle.com,
        joro@...tes.org, wanpengli@...cent.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: X86: Explicitly set the 'fault.async_page_fault'
 value in kvm_fixup_and_inject_pf_error().

On Mon, Jul 18, 2022, Yu Zhang wrote:
> kvm_fixup_and_inject_pf_error() was introduced to fixup the error code(
> e.g., to add RSVD flag) and inject the #PF to the guest, when guest
> MAXPHYADDR is smaller than the host one.
> 
> When it comes to nested, L0 is expected to intercept and fix up the #PF
> and then inject to L2 directly if
> - L2.MAXPHYADDR < L0.MAXPHYADDR and
> - L1 has no intention to intercept L2's #PF (e.g., L2 and L1 have the
>   same MAXPHYADDR value && L1 is using EPT for L2),
> instead of constructing a #PF VM Exit to L1. Currently, with PFEC_MASK
> and PFEC_MATCH both set to 0 in vmcs02, the interception and injection
> may happen on all L2 #PFs.
> 
> However, failing to initialize 'fault' in kvm_fixup_and_inject_pf_error()
> may cause the fault.async_page_fault being NOT zeroed, and later the #PF
> being treated as a nested async page fault, and then being injected to L1.
> Instead of zeroing 'fault' at the beginning of this function, we mannually
> set the value of 'fault.async_page_fault', because false is the value we
> really expect.
> 
> Fixes: 897861479c064 ("KVM: x86: Add helper functions for illegal GPA checking and page fault injection")
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=216178
> Reported-by: Yang Lixiao <lixiao.yang@...el.com>
> Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

No need for my SoB, I was just providing feedback.  Other than that, 

Reviewed-by: Sean Christopherson <seanjc@...gle.com>