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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Date:   Thu, 21 Jul 2022 17:22:14 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     Sean Christopherson <seanjc@...gle.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 Tue, Jul 19, 2022 at 07:01:41PM +0000, Sean Christopherson wrote:
> 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, 
> 
Thanks! It's a very detailed suggestion. :)

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

@Paolo Any comment on this fix, and on the test case change(https://www.spinics.net/lists/kvm/msg283600.html)? Thanks!

B.R.
Yu