[PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

[PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

[Paul Durrant]

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.

Cache pointers to the sub-leaves when CPUID is updated by the VMM and
populate the relevant information prior to entering the guest.

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

v2:
 - Make sure sub-leaf pointers are NULLed if the time leaf is removed

v3:
 - Add leaf limit check in kvm_xen_set_cpuid()

v4:
 - Update commit comment
---
 arch/x86/include/asm/kvm_host.h |  2 ++
 arch/x86/kvm/cpuid.c            |  2 ++
 arch/x86/kvm/x86.c              |  1 +
 arch/x86/kvm/xen.c              | 49 +++++++++++++++++++++++++++++++++
 arch/x86/kvm/xen.h              | 10 +++++++
 5 files changed, 64 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1038ccb7056a..f77a4940542f 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -638,6 +638,8 @@ struct kvm_vcpu_xen {
 	struct hrtimer timer;
 	int poll_evtchn;
 	struct timer_list poll_timer;
+	struct kvm_cpuid_entry2 *tsc_info_1;
+	struct kvm_cpuid_entry2 *tsc_info_2;
 };
 
 struct kvm_vcpu_arch {
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index d47222ab8e6e..eb6cd88c974a 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_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 00e23dc518e0..8b45f9975e45 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3123,6 +3123,7 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
 	if (vcpu->xen.vcpu_time_info_cache.active)
 		kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0);
 	kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
+	kvm_xen_setup_tsc_info(v);
 	return 0;
 }
 
diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 610beba35907..08e65ec6c793 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 +1858,49 @@ 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_set_cpuid(struct kvm_vcpu *vcpu)
+{
+	u32 base = 0;
+	u32 limit;
+	u32 function;
+
+	vcpu->arch.xen.tsc_info_1 = NULL;
+	vcpu->arch.xen.tsc_info_2 = NULL;
+
+	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.tsc_info_1 = kvm_find_cpuid_entry(vcpu, function, 1);
+	vcpu->arch.xen.tsc_info_2 = kvm_find_cpuid_entry(vcpu, function, 2);
+}
+
+void kvm_xen_setup_tsc_info(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *entry = vcpu->arch.xen.tsc_info_1;
+
+	if (entry) {
+		entry->ecx = vcpu->arch.hv_clock.tsc_to_system_mul;
+		entry->edx = vcpu->arch.hv_clock.tsc_shift;
+	}
+
+	entry = vcpu->arch.xen.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..1afb663318a9 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_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_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

Re: [PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

[Sean Christopherson]

On Wed, Jun 22, 2022, Paul Durrant wrote:
> 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.
> 
> Cache pointers to the sub-leaves when CPUID is updated by the VMM and
> populate the relevant information prior to entering the guest.

All of my comments about the code still apply.

https://lore.kernel.org/all/YrMqtHzNSean+qkh@google.com

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

Cc: can go in the changelog, it's helpful info to carry with the commit as it
documents who was made aware of the patch, e.g. show who may have had a cance to
object/review.

> 
> v2:
>  - Make sure sub-leaf pointers are NULLed if the time leaf is removed
> 
> v3:
>  - Add leaf limit check in kvm_xen_set_cpuid()
> 
> v4:
>  - Update commit comment

Please start with the most recent verison and work backardwards, that way reviewers
can quickly see the delta for _this_ version.  I.e.


v4:

v3:

v2:

v1:

RE: [PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if present

[Durrant, Paul]

> -----Original Message-----
> From: Sean Christopherson <seanjc@google.com>
> Sent: 27 June 2022 16:19
> To: Durrant, Paul <pdurrant@amazon.co.uk>
> Cc: x86@kernel.org; kvm@vger.kernel.org; linux-kernel@vger.kernel.org; David Woodhouse
> <dwmw2@infradead.org>; Paolo Bonzini <pbonzini@redhat.com>; Vitaly Kuznetsov <vkuznets@redhat.com>;
> Wanpeng Li <wanpengli@tencent.com>; Jim Mattson <jmattson@google.com>; Joerg Roedel <joro@8bytes.org>;
> Thomas Gleixner <tglx@linutronix.de>; Ingo Molnar <mingo@redhat.com>; Borislav Petkov <bp@alien8.de>;
> Dave Hansen <dave.hansen@linux.intel.com>; H. Peter Anvin <hpa@zytor.com>
> Subject: RE: [EXTERNAL][PATCH v4] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info) sub-leaves, if
> present
> 
> CAUTION: This email originated from outside of the organization. Do not click links or open
> attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> On Wed, Jun 22, 2022, Paul Durrant wrote:
> > 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.
> >
> > Cache pointers to the sub-leaves when CPUID is updated by the VMM and
> > populate the relevant information prior to entering the guest.
> 
> All of my comments about the code still apply.
> 
> https://lore.kernel.org/all/YrMqtHzNSean+qkh@google.com
> 

Apologies. Not sure how I missed them; I'll send a response shortly.

> > Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> > ---
> > Cc: David Woodhouse <dwmw2@infradead.org>
> 
> Cc: can go in the changelog, it's helpful info to carry with the commit as it
> documents who was made aware of the patch, e.g. show who may have had a cance to
> object/review.
> 
> >
> > v2:
> >  - Make sure sub-leaf pointers are NULLed if the time leaf is removed
> >
> > v3:
> >  - Add leaf limit check in kvm_xen_set_cpuid()
> >
> > v4:
> >  - Update commit comment
> 
> Please start with the most recent verison and work backardwards, that way reviewers
> can quickly see the delta for _this_ version.  I.e.
> 
> 
> v4:
> 
> v3:
> 
> v2:
> 
> v1:

Ok.

  Paul