On Thu, 2021-09-02 at 17:34 +0000, Sean Christopherson wrote:
On Wed, Aug 11, 2021, Maxim Levitsky wrote:
On Wed, 2021-08-11 at 15:29 +0300, Maxim Levitsky wrote:
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c index e45259177009..19f54b07161a 100644 --- a/arch/x86/kvm/svm/svm.c +++ b/arch/x86/kvm/svm/svm.c @@ -233,6 +233,8 @@ static const u32 msrpm_ranges[] = {0, 0xc0000000, 0xc0010000}; #define MSRS_RANGE_SIZE 2048 #define MSRS_IN_RANGE (MSRS_RANGE_SIZE * 8 / 2) +static int svm_handle_invalid_exit(struct kvm_vcpu *vcpu, u64 exit_code);
u32 svm_msrpm_offset(u32 msr) { u32 offset; @@ -1153,6 +1155,22 @@ static void svm_recalc_instruction_intercepts(struct kvm_vcpu *vcpu, } } +static void svm_init_force_exceptions_intercepts(struct vcpu_svm *svm) +{
- int exc;
- svm->force_intercept_exceptions_mask = force_intercept_exceptions_mask;
Ah, the param is being snapshotted on vCPU creation, hence the writable module param. That works, though it'd be better to snapshot it on a per-VM basic, not per-vCPU, and do so in common x86 code so that the param doesn't need to be exported.
I have nothing against that.
- for (exc = 0 ; exc < 32 ; exc++) {
for_each_set_bit()
I used a helper function instead, IMHO a bit cleaner.
if (!(svm->force_intercept_exceptions_mask & (1 << exc)))continue;/* Those are defined to have undefined behavior in the SVM spec */if (exc != 2 && exc != 9)Maybe add a pr_warn_once() to let the user know they done messed up?
And given that there are already intercepts with undefined behavior, it's probably best to disallow intercepting anything we aren't 100% postive will be handled correctly, e.g. intercepting vector 31 is nonsensical at this time.
Or I think I'll just drop this check altogether - this is a debug feature anyway.
continue;set_exception_intercept(svm, exc);...
+static int gen_exc_interception(struct kvm_vcpu *vcpu) +{
- /*
* Generic exception intercept handler which forwards a guest exception* as-is to the guest.* For exceptions that don't have a special intercept handler.** Used only for 'force_intercept_exceptions_mask' KVM debug feature.*/- struct vcpu_svm *svm = to_svm(vcpu);
- int exc = svm->vmcb->control.exit_code - SVM_EXIT_EXCP_BASE;
- /* SVM doesn't provide us with an error code for the #DF */
- u32 err_code = exc == DF_VECTOR ? 0 : svm->vmcb->control.exit_info_1;
Might be better to handle this in the x86_exception_has_error_code() path to avoid confusing readers with respect to exceptions that don't have an error code, e.g.
else if (x86_exception_has_error_code(exc)) { /* SVM doesn't provide the error code on #DF :-( */ if (exc == DF_VECTOR) kvm_queue_exception_e(vcpu, exc, 0); else kvm_queue_exception_e(vcpu, exc, svm->vmcb->control.exit_info_1); } else { ... }
Alternatively, can we zero svm->vmcb->control.exit_info_1 on #DF to make it more obvious that SVM leaves stale data in exit_info_1 (assuming that's true)? E.g.
...
if (exc == TS_VECTOR) { ... } else if (x86_exception_has_error_code(exc)) { /* SVM doesn't provide the error code on #DF :-( */ if (exc == DF_VECTOR) svm->vmcb->control.exit_info_1 = 0;
kvm_queue_exception_e(vcpu, exc, svm->vmcb->control.exit_info_1);} else { ... }
Makes sense.
- if (!(svm->force_intercept_exceptions_mask & (1 << exc)))
BIT(exc)
I added a helper function in common x86 code for this.
return svm_handle_invalid_exit(vcpu, svm->vmcb->control.exit_code);- if (exc == TS_VECTOR) {
/** SVM doesn't provide us with an error code to be able to* re-inject the #TS exception, so just disable its* intercept, and let the guest re-execute the instruction.*/vmcb_clr_intercept(&svm->vmcb01.ptr->control,INTERCEPT_EXCEPTION_OFFSET + TS_VECTOR);Maybe just disallow intercepting #TS altogether? Or does this fall into your Win98 use case? :-)
Win98 does indeed generate few #TS exceptions but so far I haven't noticed any issues related to task switches. Anyway I would like to intercept as much as possible since this is a debug feature. A single interception is still better that nothing.
recalc_intercepts(svm);- } else if (x86_exception_has_error_code(exc))
kvm_queue_exception_e(vcpu, exc, err_code);- else
kvm_queue_exception(vcpu, exc);- return 1;
+}
static bool is_erratum_383(void) { int err, i; @@ -3065,6 +3131,10 @@ static int (*const svm_exit_handlers[])(struct kvm_vcpu *vcpu) = { [SVM_EXIT_WRITE_DR5] = dr_interception, [SVM_EXIT_WRITE_DR6] = dr_interception, [SVM_EXIT_WRITE_DR7] = dr_interception,
- [SVM_EXIT_EXCP_BASE ...
- SVM_EXIT_EXCP_BASE + 31] = gen_exc_interception,
This generates a Sparse warning due to the duplicate initializer. IMO that's a very good warning as I have zero idea how the compiler actually handles this particular scenario, e.g. do later entries take priority, is it technically "undefined" behavior, etc...
arch/x86/kvm/svm/svm.c:3065:10: warning: Initializer entry defined twice arch/x86/kvm/svm/svm.c:3067:29: also defined here
I don't have a clever solution though :-('
Good catch. I thought that this would make sense but standards never make sense. I'll do this manually.
- [SVM_EXIT_EXCP_BASE + DB_VECTOR] = db_interception, [SVM_EXIT_EXCP_BASE + BP_VECTOR] = bp_interception, [SVM_EXIT_EXCP_BASE + UD_VECTOR] = ud_interception,
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 524d943f3efc..187ada7c5b03 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -196,6 +196,7 @@ struct vcpu_svm { bool ghcb_sa_free; bool guest_state_loaded;
- u32 force_intercept_exceptions_mask;
}; struct svm_cpu_data { @@ -351,8 +352,11 @@ static inline void clr_exception_intercept(struct vcpu_svm *svm, u32 bit) struct vmcb *vmcb = svm->vmcb01.ptr; WARN_ON_ONCE(bit >= 32);
- vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit);
- if ((1 << bit) & svm->force_intercept_exceptions_mask)
BIT(bit)
Fixed with helper function as well.
return;- vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit); recalc_intercepts(svm);
}
Thanks for the review! Best regards, Maxim Levitsky