Re: [PATCH v19 101/130] KVM: TDX: handle ept violation/misconfig exit

Isaku Yamahata
2024-05-01T15:56:22Z

On Tue, Apr 30, 2024 at 01:47:07PM -0700,
Reinette Chatre <reinette.chatre@intel.com> wrote:

> Hi Isaku,
>
> On 4/3/2024 11:42 AM, Isaku Yamahata wrote:
> > On Mon, Apr 01, 2024 at 12:10:58PM +0800,
> > Chao Gao <chao.gao@intel.com> wrote:
> >
> >>> +static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
> >>> +{
> >>> + unsigned long exit_qual;
> >>> +
> >>> + if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu))) {
> >>> + /*
> >>> + * Always treat SEPT violations as write faults. Ignore the
> >>> + * EXIT_QUALIFICATION reported by TDX-SEAM for SEPT violations.
> >>> + * TD private pages are always RWX in the SEPT tables,
> >>> + * i.e. they're always mapped writable. Just as importantly,
> >>> + * treating SEPT violations as write faults is necessary to
> >>> + * avoid COW allocations, which will cause TDAUGPAGE failures
> >>> + * due to aliasing a single HPA to multiple GPAs.
> >>> + */
> >>> +#define TDX_SEPT_VIOLATION_EXIT_QUAL EPT_VIOLATION_ACC_WRITE
> >>> + exit_qual = TDX_SEPT_VIOLATION_EXIT_QUAL;
> >>> + } else {
> >>> + exit_qual = tdexit_exit_qual(vcpu);
> >>> + if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
> >>
> >> Unless the CPU has a bug, instruction fetch in TD from shared memory causes a
> >> #PF. I think you can add a comment for this.
> >
> > Yes.
> >
> >
> >> Maybe KVM_BUG_ON() is more appropriate as it signifies a potential bug.
> >
> > Bug of what component? CPU. If so, I think KVM_EXIT_INTERNAL_ERROR +
> > KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON is more appropriate.
> >
>
> Is below what you have in mind?

Yes. data[0] should be the raw value of exit reason if possible.
data[2] should be exit_qual. Hmm, I don't find document on data[] for
KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON.
Qemu doesn't assumt ndata = 2. Just report all data within ndata.

> diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> index 499c6cd9633f..bd30b4c4d710 100644
> --- a/arch/x86/kvm/vmx/tdx.c
> +++ b/arch/x86/kvm/vmx/tdx.c
> @@ -1305,11 +1305,18 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
> } else {
> exit_qual = tdexit_exit_qual(vcpu);
> if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
> + /*
> + * Instruction fetch in TD from shared memory
> + * causes a #PF.
> + */
> pr_warn("kvm: TDX instr fetch to shared GPA = 0x%lx @ RIP = 0x%lx\n",
> tdexit_gpa(vcpu), kvm_rip_read(vcpu));
> - vcpu->run->exit_reason = KVM_EXIT_EXCEPTION;
> - vcpu->run->ex.exception = PF_VECTOR;
> - vcpu->run->ex.error_code = exit_qual;
> + vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
> + vcpu->run->internal.suberror =
> + KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
> + vcpu->run->internal.ndata = 2;
> + vcpu->run->internal.data[0] = EXIT_REASON_EPT_VIOLATION;
> + vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
> return 0;
> }
> }
>
> Thank you
>
> Reinette
>
>
>

--
Isaku Yamahata <isaku.yamahata@intel.com>