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Message-ID: <YsynoyUb4zrMBhRU@google.com>
Date: Mon, 11 Jul 2022 22:43:47 +0000
From: Sean Christopherson <seanjc@...gle.com>
To: Paul Durrant <pdurrant@...zon.com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
David Woodhouse <dwmw2@...radead.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH v5] KVM: x86/xen: Update Xen CPUID Leaf 4 (tsc info)
sub-leaves, if present
On Wed, Jun 29, 2022, Paul Durrant wrote:
> 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;
I would prefer to follow vcpu->arch.kvm_cpuid_base and capture the base CPUID
function. I have a hard time believing this will be the only case where KVM needs
to query XEN CPUID leafs. And cpuid_tsc_info is a confusing name given the helper
kvm_xen_setup_tsc_info(); it's odd to see a "setup" helper immediately consume a
variable with the same name.
It'll incur another CPUID lookup in the update path to check the limit, but again
that should be a rare operation so it doesn't seem too onerous.
> 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);
Any objection to s/setup/update? KVM Xen uses "setup" for things like configuring
the event channel using userspace input, whereas this is purely updating existing
data structures.
> }
>
> 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;
Rather than open code a variant of kvm_update_kvm_cpuid_base(), that helper can
be tweaked to take a signature. Along with a patch to provide a #define for Xen's
signature as a string, this entire function becomes a one-liner.
If the below looks ok (won't compile, needs prep patches), I'll test and post a
proper mini-series.
---
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 | 30 ++++++++++++++++++++++++++++++
arch/x86/kvm/xen.h | 22 +++++++++++++++++++++-
5 files changed, 55 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index de5a149d0971..b2565d05fc86 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_base;
};
struct kvm_vcpu_arch {
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 0abe3adc9ae3..54ed51799b8d 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
@@ -309,6 +310,7 @@ 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 567d13405445..a624293c66c8 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_update_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..3fc0c194b813 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 +1858,30 @@ 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_update_tsc_info(struct kvm_vcpu *vcpu)
+{
+ struct kvm_cpuid_entry2 *entry;
+ u32 function;
+
+ if (!vcpu->arch.xen.cpuid_base)
+ return;
+
+ entry = kvm_find_cpuid_entry(vcpu, vcpu->arch.xen.cpuid_base, 0);
+ if (WARN_ON_ONCE(!entry))
+ return;
+
+ function = vcpu->arch.xen.cpuid_base | XEN_CPUID_LEAF(3);
+ if (function > entry->eax)
+ return;
+
+ entry = kvm_find_cpuid_entry(vcpu, function, 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, function, 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..b8161b99b82a 100644
--- a/arch/x86/kvm/xen.h
+++ b/arch/x86/kvm/xen.h
@@ -9,9 +9,14 @@
#ifndef __ARCH_X86_KVM_XEN_H__
#define __ARCH_X86_KVM_XEN_H__
-#ifdef CONFIG_KVM_XEN
#include <linux/jump_label_ratelimit.h>
+#include <asm/xen/cpuid.h>
+
+#include "cpuid.h"
+
+#ifdef CONFIG_KVM_XEN
+
extern struct static_key_false_deferred kvm_xen_enabled;
int __kvm_xen_has_interrupt(struct kvm_vcpu *vcpu);
@@ -32,6 +37,13 @@ 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_update_tsc_info(struct kvm_vcpu *vcpu);
+
+static inline void kvm_xen_after_set_cpuid(struct kvm_vcpu *vcpu)
+{
+ vcpu->arch.xen.cpuid_base =
+ kvm_get_hypervisor_cpuid_base(vcpu, XEN_CPUID_SIGNATURE);
+}
static inline bool kvm_xen_msr_enabled(struct kvm *kvm)
{
@@ -135,6 +147,14 @@ 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_update_tsc_info(struct kvm_vcpu *vcpu)
+{
+}
#endif
int kvm_xen_hypercall(struct kvm_vcpu *vcpu);
base-commit: b08b2f54c49d8f96a22107c444d500dff73ec2a6
--
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