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Message-ID: <8b4fda17-07c3-4633-bf61-8b3829384c29@xen.org>
Date: Wed, 1 Nov 2023 17:02:23 +0000
From: Paul Durrant <xadimgnik@...il.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Jonathan Corbet <corbet@....net>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
David Woodhouse <dwmw2@...radead.org>, kvm@...r.kernel.org,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] KVM x86/xen: add an override for
PVCLOCK_TSC_STABLE_BIT
On 01/11/2023 16:46, Sean Christopherson wrote:
> On Wed, Nov 01, 2023, Paul Durrant wrote:
>> @@ -3231,12 +3245,15 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
>> vcpu->hv_clock.flags = pvclock_flags;
>>
>> if (vcpu->pv_time.active)
>> - kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0);
>> + kvm_setup_guest_pvclock(v, &vcpu->pv_time, 0, false);
>> +
>> if (vcpu->xen.vcpu_info_cache.active)
>> kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_info_cache,
>> - offsetof(struct compat_vcpu_info, time));
>> + offsetof(struct compat_vcpu_info, time),
>> + xen_pvclock_tsc_unstable);
>> if (vcpu->xen.vcpu_time_info_cache.active)
>> - kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0);
>> + kvm_setup_guest_pvclock(v, &vcpu->xen.vcpu_time_info_cache, 0,
>> + xen_pvclock_tsc_unstable);
>> kvm_hv_setup_tsc_page(v->kvm, &vcpu->hv_clock);
>> return 0;
>
> Please rebase, this conflicts with commit ee11ab6bb04e ("KVM: X86: Reduce size of
> kvm_vcpu_arch structure when CONFIG_KVM_XEN=n"). I can solve the conflict, but
> I really shouldn't have to.
>
> Also, your version of git should support --base, which makes life much easier for
> others when non-trivial conflicts are encountered. From maintainer-kvm-x86.rst:
>
> : Git Base
> : ~~~~~~~~
> : If you are using git version 2.9.0 or later (Googlers, this is all of you!),
> : use ``git format-patch`` with the ``--base`` flag to automatically include the
> : base tree information in the generated patches.
> :
> : Note, ``--base=auto`` works as expected if and only if a branch's upstream is
> : set to the base topic branch, e.g. it will do the wrong thing if your upstream
> : is set to your personal repository for backup purposes. An alternative "auto"
> : solution is to derive the names of your development branches based on their
> : KVM x86 topic, and feed that into ``--base``. E.g. ``x86/pmu/my_branch_name``,
> : and then write a small wrapper to extract ``pmu`` from the current branch name
> : to yield ``--base=x/pmu``, where ``x`` is whatever name your repository uses to
> : track the KVM x86 remote.
>
Ok, I'll sort that out. Thanks for the tip.
>> @@ -4531,7 +4548,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
>> KVM_XEN_HVM_CONFIG_SHARED_INFO |
>> KVM_XEN_HVM_CONFIG_EVTCHN_2LEVEL |
>> - KVM_XEN_HVM_CONFIG_EVTCHN_SEND;
>> + KVM_XEN_HVM_CONFIG_EVTCHN_SEND |
>> + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE;
>> if (sched_info_on())
>> r |= KVM_XEN_HVM_CONFIG_RUNSTATE |
>> KVM_XEN_HVM_CONFIG_RUNSTATE_UPDATE_FLAG;
>> diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
>> index 40edf4d1974c..7699d94f190b 100644
>> --- a/arch/x86/kvm/xen.c
>> +++ b/arch/x86/kvm/xen.c
>> @@ -1111,9 +1111,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
>>
>> int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc)
>> {
>> + bool update_pvclock = false;
>> +
>> /* Only some feature flags need to be *enabled* by userspace */
>> u32 permitted_flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
>> - KVM_XEN_HVM_CONFIG_EVTCHN_SEND;
>> + KVM_XEN_HVM_CONFIG_EVTCHN_SEND |
>> + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE;
>>
>> if (xhc->flags & ~permitted_flags)
>> return -EINVAL;
>> @@ -1134,9 +1137,19 @@ int kvm_xen_hvm_config(struct kvm *kvm, struct kvm_xen_hvm_config *xhc)
>> else if (!xhc->msr && kvm->arch.xen_hvm_config.msr)
>> static_branch_slow_dec_deferred(&kvm_xen_enabled);
>>
>> + if ((kvm->arch.xen_hvm_config.flags &
>> + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE) !=
>> + (xhc->flags &
>> + KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE))
>> + update_pvclock = true;
>
> Rather than a boolean and the above, which is a bit hard to parse, what about
> taking a snapshot of the old flags and then doing an XOR?
>
> /* Only some feature flags need to be *enabled* by userspace */
> u32 permitted_flags = KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL |
> KVM_XEN_HVM_CONFIG_EVTCHN_SEND |
> KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE;
> u32 old_flags;
>
> if (xhc->flags & ~permitted_flags)
> return -EINVAL;
>
> /*
> * With hypercall interception the kernel generates its own
> * hypercall page so it must not be provided.
> */
> if ((xhc->flags & KVM_XEN_HVM_CONFIG_INTERCEPT_HCALL) &&
> (xhc->blob_addr_32 || xhc->blob_addr_64 ||
> xhc->blob_size_32 || xhc->blob_size_64))
> return -EINVAL;
>
> mutex_lock(&kvm->arch.xen.xen_lock);
>
> if (xhc->msr && !kvm->arch.xen_hvm_config.msr)
> static_branch_inc(&kvm_xen_enabled.key);
> else if (!xhc->msr && kvm->arch.xen_hvm_config.msr)
> static_branch_slow_dec_deferred(&kvm_xen_enabled);
>
> old_flags = kvm->arch.xen_hvm_config.flags;
> memcpy(&kvm->arch.xen_hvm_config, xhc, sizeof(*xhc));
>
> mutex_unlock(&kvm->arch.xen.xen_lock);
>
> if ((old_flags ^ xhc->flags) & KVM_XEN_HVM_CONFIG_PVCLOCK_TSC_UNSTABLE)
> kvm_make_all_cpus_request(kvm, KVM_REQ_CLOCK_UPDATE);
>
> return 0;
Sure, I can do it that way if you prefer.
Paul
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