Re: [PATCH v4 2/9] KVM: TDX: Check if there is valid exit infos based on vp_enter_ret

[Xiaoyao Li]

On 8/20/2026 12:39 AM, Edgecombe, Rick P wrote:
> On Wed, 2026-08-19 at 17:48 +0800, Xiaoyao Li wrote:
> > Check if there is valid exit info based on vp_enter_ret instead of relying
> > on the clobbered Exit Reason, in tdx_get_exit_info().
> >
> > Current KVM uses "Exit Reason is not equal to the synthesized invalid
> > Exit Reason, -1u," as the condition to identify there is a real TD Exit
> > and valid exit infos.  However, there is one issue with this approach:
> > KVM updates the Exit Reason to the synthesized invalid Exit Reason for
> > real EPT MISCONFIG as well.  This is a false positive for real EPT
> > MISCONFIG, which has valid exit infos.
> >
> > Though the issue can be addressed by changing the handling for real EPT
> > MISCONFIG to not update the Exit Reason to the synthesized one, relying
> > on the clobbered Exit Reason itself is brittle.  Instead, check
> > vp_enter_ret directly to identify if it is a valid Exit Reason.
> >
> > Fixes: da407fe45908 ("KVM: TDX: Handle EPT violation/misconfig exit")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
>
> This series has grown unfortunately, and I wasn't able to catch up on the
> threads from yesterday. Can we really not put this one in the non-stable patches
> at the end? Or maybe you can explain why it's needed?

It was suggested[1] (or requested) by Sean.

I agree that it's not mandatory for enabling Bus Lock VM exit for TDX. 
But considering that without this patch, both patch 3 and patch 4 need 
to change the line

	if (*reason != -1u)

in tdx_get_exit_info(), which brings unnecessary code churn. And given 
the patch number needs to increase anyway in this v4. So I just put this 
patch in to make patch 3 and patch 4 simpler.

[1] https://lore.kernel.org/all/an0N0vHwsYEqjpRe@xxxxxxxxxx/

> Also "KVM: VMX: Preserve negative return value in vmx_handle_exit() with bus
> lock detected"?

It was suggested[2] by Sean.

(Since there are discussions happening in the cover letter thread about 
it. Let's continue the discussion there.)

[2] https://lore.kernel.org/all/an0KokdtSXE2GmM1@xxxxxxxxxx/