[PATCH v5] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

* [PATCH v5] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present
@ 2022-06-29 13:05 Paul Durrant
  2022-07-11 22:43 ` Sean Christopherson
  0 siblings, 1 reply; 5+ messages in thread
From: Paul Durrant @ 2022-06-29 13:05 UTC (permalink / raw)
  To: x86, kvm, linux-kernel
  Cc: Paul Durrant, David Woodhouse, Paolo Bonzini,
	Sean Christopherson, Vitaly Kuznetsov, Wanpeng Li, Jim Mattson,
	Joerg Roedel, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
	Dave Hansen, H. Peter Anvin

The scaling information in subleaf 1 should match the values set by KVM in
the 'vcpu_info' sub-structure 'time_info' (a.k.a. pvclock_vcpu_time_info)
which is shared with the guest, but is not directly available to the VMM.
The offset values are not set since a TSC offset is already applied.
The TSC frequency should also be set in sub-leaf 2.

Signed-off-by: Paul Durrant <pdurrant@amazon.com>
---
Cc: David Woodhouse <dwmw2@infradead.org>

v5:
 - Drop the caching of the CPUID entry pointers and only update the
   sub-leaves if the CPU frequency has actually changed

v4:
 - Update commit comment

v3:
 - Add leaf limit check in kvm_xen_set_cpuid()

v2:
 - Make sure sub-leaf pointers are NULLed if the time leaf is removed
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/cpuid.c            |  2 ++
 arch/x86/kvm/x86.c              |  1 +
 arch/x86/kvm/xen.c              | 51 +++++++++++++++++++++++++++++++++
 arch/x86/kvm/xen.h              | 10 +++++++
 5 files changed, 65 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 88a3026ee163..abb0a39f60eb 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -638,6 +638,7 @@ struct kvm_vcpu_xen {
 	struct hrtimer timer;
 	int poll_evtchn;
 	struct timer_list poll_timer;
+	u32 cpuid_tsc_info;
 };
 
 struct kvm_vcpu_arch {
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d47222ab8e6e..544d0f823ee5 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -25,6 +25,7 @@
 #include "mmu.h"
 #include "trace.h"
 #include "pmu.h"
+#include "xen.h"
 
 /*
  * Unlike "struct cpuinfo_x86.x86_capability", kvm_cpu_caps doesn't need to be
@@ -310,6 +311,7 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
 	    __cr4_reserved_bits(guest_cpuid_has, vcpu);
 
 	kvm_hv_set_cpuid(vcpu);
+	kvm_xen_after_set_cpuid(vcpu);
 
 	/* Invoke the vendor callback only after the above state is updated. */
 	static_call(kvm_x86_vcpu_after_set_cpuid)(vcpu);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 031678eff28e..29ed665c51db 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3110,6 +3110,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 				   &vcpu->hv_clock.tsc_shift,
 				   &vcpu->hv_clock.tsc_to_system_mul);
 		vcpu->hw_tsc_khz = tgt_tsc_khz;
+		kvm_xen_setup_tsc_info(v);
 	}
 
 	vcpu->hv_clock.tsc_timestamp = tsc_timestamp;
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 610beba35907..c84424d5c8b6 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -10,6 +10,9 @@
 #include "xen.h"
 #include "hyperv.h"
 #include "lapic.h"
+#include "cpuid.h"
+
+#include <asm/xen/cpuid.h>
 
 #include <linux/eventfd.h>
 #include <linux/kvm_host.h>
@@ -1855,3 +1858,51 @@ void kvm_xen_destroy_vm(struct kvm *kvm)
 	if (kvm->arch.xen_hvm_config.msr)
 		static_branch_slow_dec_deferred(&kvm_xen_enabled);
 }
+
+void kvm_xen_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+	u32 base = 0;
+	u32 limit;
+	u32 function;
+
+	vcpu->arch.xen.cpuid_tsc_info = 0;
+
+	for_each_possible_hypervisor_cpuid_base(function) {
+		struct kvm_cpuid_entry2 *entry = kvm_find_cpuid_entry(vcpu, function, 0);
+
+		if (entry &&
+		    entry->ebx == XEN_CPUID_SIGNATURE_EBX &&
+		    entry->ecx == XEN_CPUID_SIGNATURE_ECX &&
+		    entry->edx == XEN_CPUID_SIGNATURE_EDX) {
+			base = function;
+			limit = entry->eax;
+			break;
+		}
+	}
+	if (!base)
+		return;
+
+	function = base | XEN_CPUID_LEAF(3);
+	if (function > limit)
+		return;
+
+	vcpu->arch.xen.cpuid_tsc_info = function;
+}
+
+void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *entry;
+
+	if (!vcpu->arch.xen.cpuid_tsc_info)
+		return;
+
+	entry = kvm_find_cpuid_entry(vcpu, vcpu->arch.xen.cpuid_tsc_info, 1);
+	if (entry) {
+		entry->ecx = vcpu->arch.hv_clock.tsc_to_system_mul;
+		entry->edx = vcpu->arch.hv_clock.tsc_shift;
+	}
+
+	entry = kvm_find_cpuid_entry(vcpu, vcpu->arch.xen.cpuid_tsc_info, 2);
+	if (entry)
+		entry->eax = vcpu->arch.hw_tsc_khz;
+}
diff --git a/arch/x86/kvm/xen.h b/arch/x86/kvm/xen.h
index 532a535a9e99..b2ca434431d6 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -32,6 +32,8 @@ int kvm_xen_set_evtchn_fast(struct kvm_xen_evtchn *xe,
 int kvm_xen_setup_evtchn(struct kvm *kvm,
 			 struct kvm_kernel_irq_routing_entry *e,
 			 const struct kvm_irq_routing_entry *ue);
+void kvm_xen_after_set_cpuid(struct kvm_vcpu *vcpu);
+void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu);
 
 static inline bool kvm_xen_msr_enabled(struct kvm *kvm)
 {
@@ -135,6 +137,14 @@ static inline bool kvm_xen_timer_enabled(struct kvm_vcpu *vcpu)
 {
 	return false;
 }
+
+static inline void kvm_xen_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+}
+
+static inline void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu)
+{
+}
 #endif
 
 int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
-- 
2.20.1


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