On Wed, Jun 07, 2023 at 12:27:33PM -0700,
Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> On 6/7/23 11:53, Isaku Yamahata wrote:
> >>> VMX enabling, and KVM is the only user of TDX. This implementation
> >>> chooses to make KVM itself responsible for enabling VMX before using
> >>> TDX and let the rest of the kernel stay blissfully unaware of VMX.
> >>>
> >>> The current TDX_MODULE_CALL macro handles neither #GP nor #UD. The
> >>> kernel would hit Oops if SEAMCALL were mistakenly made w/o enabling VMX
> >>> first. Architecturally, there is no CPU flag to check whether the CPU
> >>> is in VMX operation. Also, if a BIOS were buggy, it could still report
> >>> valid TDX private KeyIDs when TDX actually couldn't be enabled.
> >> I'm not sure this is a great justification. If the BIOS is lying to the
> >> OS, we _should_ oops.
> >>
> >> How else can this happen other than silly kernel bugs. It's OK to oops
> >> in the face of silly kernel bugs.
> > TDX KVM + reboot can hit #UD. On reboot, VMX is disabled (VMXOFF) via
> > syscore.shutdown callback. However, guest TD can be still running to issue
> > SEAMCALL resulting in #UD.
> >
> > Or we can postpone the change and make the TDX KVM patch series carry a patch
> > for it.
>
> How does the existing KVM use of VMLAUNCH/VMRESUME avoid that problem?
extable. From arch/x86/kvm/vmx/vmenter.S
.Lvmresume:
vmresume
jmp .Lvmfail
.Lvmlaunch:
vmlaunch
jmp .Lvmfail
_ASM_EXTABLE(.Lvmresume, .Lfixup)
_ASM_EXTABLE(.Lvmlaunch, .Lfixup)
--
Isaku Yamahata <isaku.yamahata@xxxxxxxxx>
