Commit cc9cfddb authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Paolo Bonzini
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KVM: x86: hyper-v: Track Hyper-V TSC page status 



Create an infrastructure for tracking Hyper-V TSC page status, i.e. if it
was updated from guest/host side or if we've failed to set it up (because
e.g. guest wrote some garbage to HV_X64_MSR_REFERENCE_TSC) and there's no
need to retry.

Also, in a hypothetical situation when we are in 'always catchup' mode for
TSC we can now avoid contending 'hv->hv_lock' on every guest enter by
setting the state to HV_TSC_PAGE_BROKEN after compute_tsc_page_parameters()
returns false.

Check for HV_TSC_PAGE_SET state instead of '!hv->tsc_ref.tsc_sequence' in
get_time_ref_counter() to properly handle the situation when we failed to
write the updated TSC page values to the guest.

Signed-off-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Message-Id: <20210316143736.964151-4-vkuznets@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent e880c6ea

arch/x86/include/asm/kvm_host.h

+17 −0
Original line number Diff line number Diff line
@@ -884,12 +884,29 @@ struct kvm_hv_syndbg { 
	u64 options;

};



/* Current state of Hyper-V TSC page clocksource */

enum hv_tsc_page_status {

	/* TSC page was not set up or disabled */

	HV_TSC_PAGE_UNSET = 0,

	/* TSC page MSR was written by the guest, update pending */

	HV_TSC_PAGE_GUEST_CHANGED,

	/* TSC page MSR was written by KVM userspace, update pending */

	HV_TSC_PAGE_HOST_CHANGED,

	/* TSC page was properly set up and is currently active  */

	HV_TSC_PAGE_SET,

	/* TSC page is currently being updated and therefore is inactive */

	HV_TSC_PAGE_UPDATING,

	/* TSC page was set up with an inaccessible GPA */

	HV_TSC_PAGE_BROKEN,

};



/* Hyper-V emulation context */

struct kvm_hv {

	struct mutex hv_lock;

	u64 hv_guest_os_id;

	u64 hv_hypercall;

	u64 hv_tsc_page;

	enum hv_tsc_page_status hv_tsc_page_status;



	/* Hyper-v based guest crash (NT kernel bugcheck) parameters */

	u64 hv_crash_param[HV_X64_MSR_CRASH_PARAMS];

arch/x86/kvm/hyperv.c

+35 −14
Original line number Diff line number Diff line
@@ -520,10 +520,10 @@ static u64 get_time_ref_counter(struct kvm *kvm) 
	u64 tsc;



	/*

	 * The guest has not set up the TSC page or the clock isn't

	 * stable, fall back to get_kvmclock_ns.

	 * Fall back to get_kvmclock_ns() when TSC page hasn't been set up,

	 * is broken, disabled or being updated.

	 */

	if (!hv->tsc_ref.tsc_sequence)

	if (hv->hv_tsc_page_status != HV_TSC_PAGE_SET)

		return div_u64(get_kvmclock_ns(kvm), 100);



	vcpu = kvm_get_vcpu(kvm, 0);
@@ -1087,7 +1087,8 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, 
	BUILD_BUG_ON(sizeof(tsc_seq) != sizeof(hv->tsc_ref.tsc_sequence));

	BUILD_BUG_ON(offsetof(struct ms_hyperv_tsc_page, tsc_sequence) != 0);



	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))

	if (hv->hv_tsc_page_status == HV_TSC_PAGE_BROKEN ||

	    hv->hv_tsc_page_status == HV_TSC_PAGE_UNSET)

		return;



	mutex_lock(&hv->hv_lock);
@@ -1101,7 +1102,7 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, 
	 */

	if (unlikely(kvm_read_guest(kvm, gfn_to_gpa(gfn),

				    &tsc_seq, sizeof(tsc_seq))))

		goto out_unlock;

		goto out_err;



	/*

	 * While we're computing and writing the parameters, force the
@@ -1110,15 +1111,15 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, 
	hv->tsc_ref.tsc_sequence = 0;

	if (kvm_write_guest(kvm, gfn_to_gpa(gfn),

			    &hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence)))

		goto out_unlock;

		goto out_err;



	if (!compute_tsc_page_parameters(hv_clock, &hv->tsc_ref))

		goto out_unlock;

		goto out_err;



	/* Ensure sequence is zero before writing the rest of the struct.  */

	smp_wmb();

	if (kvm_write_guest(kvm, gfn_to_gpa(gfn), &hv->tsc_ref, sizeof(hv->tsc_ref)))

		goto out_unlock;

		goto out_err;



	/*

	 * Now switch to the TSC page mechanism by writing the sequence.
@@ -1131,8 +1132,15 @@ void kvm_hv_setup_tsc_page(struct kvm *kvm, 
	smp_wmb();



	hv->tsc_ref.tsc_sequence = tsc_seq;

	kvm_write_guest(kvm, gfn_to_gpa(gfn),

			&hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence));

	if (kvm_write_guest(kvm, gfn_to_gpa(gfn),

			    &hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence)))

		goto out_err;



	hv->hv_tsc_page_status = HV_TSC_PAGE_SET;

	goto out_unlock;



out_err:

	hv->hv_tsc_page_status = HV_TSC_PAGE_BROKEN;

out_unlock:

	mutex_unlock(&hv->hv_lock);

}
@@ -1142,7 +1150,8 @@ void kvm_hv_invalidate_tsc_page(struct kvm *kvm) 
	struct kvm_hv *hv = to_kvm_hv(kvm);

	u64 gfn;



	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))

	if (hv->hv_tsc_page_status == HV_TSC_PAGE_BROKEN ||

	    hv->hv_tsc_page_status == HV_TSC_PAGE_UNSET)

		return;



	mutex_lock(&hv->hv_lock);
@@ -1150,11 +1159,16 @@ void kvm_hv_invalidate_tsc_page(struct kvm *kvm) 
	if (!(hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE))

		goto out_unlock;



	/* Preserve HV_TSC_PAGE_GUEST_CHANGED/HV_TSC_PAGE_HOST_CHANGED states */

	if (hv->hv_tsc_page_status == HV_TSC_PAGE_SET)

		hv->hv_tsc_page_status = HV_TSC_PAGE_UPDATING;



	gfn = hv->hv_tsc_page >> HV_X64_MSR_TSC_REFERENCE_ADDRESS_SHIFT;



	hv->tsc_ref.tsc_sequence = 0;

	kvm_write_guest(kvm, gfn_to_gpa(gfn),

			&hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence));

	if (kvm_write_guest(kvm, gfn_to_gpa(gfn),

			    &hv->tsc_ref, sizeof(hv->tsc_ref.tsc_sequence)))

		hv->hv_tsc_page_status = HV_TSC_PAGE_BROKEN;



out_unlock:

	mutex_unlock(&hv->hv_lock);
@@ -1216,8 +1230,15 @@ static int kvm_hv_set_msr_pw(struct kvm_vcpu *vcpu, u32 msr, u64 data, 
	}

	case HV_X64_MSR_REFERENCE_TSC:

		hv->hv_tsc_page = data;

		if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE)

		if (hv->hv_tsc_page & HV_X64_MSR_TSC_REFERENCE_ENABLE) {

			if (!host)

				hv->hv_tsc_page_status = HV_TSC_PAGE_GUEST_CHANGED;

			else

				hv->hv_tsc_page_status = HV_TSC_PAGE_HOST_CHANGED;

			kvm_make_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu);

		} else {

			hv->hv_tsc_page_status = HV_TSC_PAGE_UNSET;

		}

		break;

	case HV_X64_MSR_CRASH_P0 ... HV_X64_MSR_CRASH_P4:

		return kvm_hv_msr_set_crash_data(kvm,