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Date: Tue, 12 Jul 2022 08:37:09 +0000
From: "Durrant, Paul" <pdurrant@...zon.co.uk>
To: Sean Christopherson <seanjc@...gle.com>
CC: "x86@...nel.org" <x86@...nel.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...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
> -----Original Message-----
> From: Sean Christopherson <seanjc@...gle.com>
> Sent: 12 July 2022 00:44
> To: Durrant, Paul <pdurrant@...zon.co.uk>
> 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: [EXTERNAL][PATCH v5] 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 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.
Sure. It is rather shrink-to-fit at the moment... no problem with capturing the base.
>
> 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.
>
We could capture the limit leaf in the general case. It's not Xen-specific after all.
> > 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.
>
Sure.
> > }
> >
> > 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.
>
Sure, but as said above, we could make capturing the limit part of the general function too. It could even be extended to capture the Hyper-V base/limit too.
As for defining the sig as a string... I guess it would be neater to use the values from the Xen header, but it'll probably make the code more ugly so a secondary definition is reasonable.
> If the below looks ok (won't compile, needs prep patches), I'll test and post a
> proper mini-series.
Ok. Thanks,
Paul
>
> ---
> 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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