Re: [PATCH v3 3/6] KVM: SVM: implement force_intercept_exceptions_mask

On Wed, 2021-08-11 at 15:29 +0300, Maxim Levitsky wrote:

Currently #TS interception is only done once. Also exception interception is not enabled for SEV guests.

Signed-off-by: Maxim Levitsky mlevitsk@redhat.com

arch/x86/include/asm/kvm_host.h | 2 + arch/x86/kvm/svm/svm.c | 70 +++++++++++++++++++++++++++++++++ arch/x86/kvm/svm/svm.h | 6 ++- arch/x86/kvm/x86.c | 5 ++- 4 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index 20daaf67a5bf..72fe03506018 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -1690,6 +1690,8 @@ int kvm_emulate_rdpmc(struct kvm_vcpu *vcpu); void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr); void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code); void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, unsigned long payload); +void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,

• 	     u32 error_code, unsigned long payload);
  

void kvm_requeue_exception(struct kvm_vcpu *vcpu, unsigned nr); void kvm_requeue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code); void kvm_inject_page_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault); 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;
• for (exc = 0 ; exc < 32 ; exc++) {

• 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)
  

• 	continue;
  

• set_exception_intercept(svm, exc);
  

I made a mistake here, during one of the refactoring I think, after I finished testing this througfully, and I noticed it now while looking again at the code.

I attached a fix for this, and I also tested more carefully that the feature works with selftests, kvm unit tests and by booting few VMs.

Best regards, Maxim Levitsky

• }

+}

static void init_vmcb(struct kvm_vcpu *vcpu) { struct vcpu_svm *svm = to_svm(vcpu); @@ -1304,6 +1322,9 @@ static void init_vmcb(struct kvm_vcpu *vcpu) enable_gif(svm);

• if (!sev_es_guest(vcpu->kvm))

• svm_init_force_exceptions_intercepts(svm);
  

} static void svm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event) @@ -1892,6 +1913,17 @@ static int pf_interception(struct kvm_vcpu *vcpu) u64 fault_address = svm->vmcb->control.exit_info_2; u64 error_code = svm->vmcb->control.exit_info_1;

• if ((svm->force_intercept_exceptions_mask & (1 << PF_VECTOR)))

• if (npt_enabled && !vcpu->arch.apf.host_apf_flags) {
  

• 	/* If the #PF was only intercepted for debug, inject
  

• 	 * it directly to the guest, since the kvm's mmu code
  

• 	 * is not ready to deal with such page faults.
  

• 	 */
  

• 	kvm_queue_exception_e_p(vcpu, PF_VECTOR,
  

• 				error_code, fault_address);
  

• 	return 1;
  

• }
  

• return kvm_handle_page_fault(vcpu, error_code, fault_address, static_cpu_has(X86_FEATURE_DECODEASSISTS) ? svm->vmcb->control.insn_bytes : NULL,

@@ -1967,6 +1999,40 @@ static int ac_interception(struct kvm_vcpu *vcpu) return 1; } +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;
• if (!(svm->force_intercept_exceptions_mask & (1 << exc)))

• 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);
  

• 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,
• [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)

• return;
  

• vmcb_clr_intercept(&vmcb->control, INTERCEPT_EXCEPTION_OFFSET + bit); recalc_intercepts(svm);

} diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 092e2fad3c0d..e5c7b8fa1f7f 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -695,12 +695,13 @@ void kvm_queue_exception_p(struct kvm_vcpu *vcpu, unsigned nr, } EXPORT_SYMBOL_GPL(kvm_queue_exception_p); -static void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,

• 		    u32 error_code, unsigned long payload)
  

+void kvm_queue_exception_e_p(struct kvm_vcpu *vcpu, unsigned nr,

• 	     u32 error_code, unsigned long payload)
  

{ kvm_multiple_exception(vcpu, nr, true, error_code, true, payload, false); } +EXPORT_SYMBOL_GPL(kvm_queue_exception_e_p); int kvm_complete_insn_gp(struct kvm_vcpu *vcpu, int err) {