From: Maxim Levitsky <mlevitsk@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>, kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
Thomas Gleixner <tglx@linutronix.de>,
Joerg Roedel <joro@8bytes.org>, Borislav Petkov <bp@alien8.de>,
Sean Christopherson <seanjc@google.com>,
Jim Mattson <jmattson@google.com>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>,
"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<linux-kernel@vger.kernel.org>,
Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH v3 06/12] KVM: x86: don't disable APICv memslot when inhibited
Date: Mon, 09 Aug 2021 21:51:34 +0300 [thread overview]
Message-ID: <d3e0ba8085a8b6054e757dac696823f1181a712b.camel@redhat.com> (raw)
In-Reply-To: <f221e94c-fb64-a859-de3c-30f883eac657@redhat.com>
On Tue, 2021-08-03 at 10:44 +0200, Paolo Bonzini wrote:
> Reviewing this patch and the next one together.
>
> On 02/08/21 20:33, Maxim Levitsky wrote:
> > +static int avic_alloc_access_page(struct kvm *kvm)
> > {
> > void __user *ret;
> > int r = 0;
> >
> > mutex_lock(&kvm->slots_lock);
> > +
> > + if (kvm->arch.apic_access_memslot_enabled)
> > goto out;
>
> This variable is overloaded between "is access enabled" and "is the
> memslot allocated". I think you should check
> kvm->arch.apicv_inhibit_reasons instead in kvm_faultin_pfn.
>
>
> > + if (!activate)
> > + kvm_zap_gfn_range(kvm, gpa_to_gfn(APIC_DEFAULT_PHYS_BASE),
> > + gpa_to_gfn(APIC_DEFAULT_PHYS_BASE + PAGE_SIZE));
> > +
>
> Off by one, the last argument of kvm_zap_gfn_range is inclusive:
Actually is it?
There are 3 uses of this function.
Two of them (kvm_post_set_cr0 and one case in update_mtrr) use 0,~0ULL which is indeed inclusive,
but for variable mtrrs I see that in var_mtrr_range this code:
*end = (*start | ~mask) + 1;
and the *end is passed to kvm_zap_gfn_range.
Another thing I noticed that I added calls to kvm_inc_notifier_count/kvm_dec_notifier_count
in the kvm_zap_gfn_range but these do seem to have non inclusive ends, thus
I need to fix them sadly if this is the case.
This depends on mmu_notifier_ops and it is not documented well.
However at least mmu_notifier_retry_hva, does assume a non inclusive range since it checks
hva >= kvm->mmu_notifier_range_start &&
hva < kvm->mmu_notifier_range_end
Also looking at the algorithm of the kvm_zap_gfn_range.
Suppose that gfn_start == gfn_end and we have a memslot with one page at gfn_start
Then:
start = max(gfn_start, memslot->base_gfn); // start = memslot->base_gfn
end = min(gfn_end, memslot->base_gfn + memslot->npages); // end = memslot->base_gfn
if (start >= end)
continue;
In this case it seems that it will do nothing. So I suspect that kvm_zap_gfn_range
actually needs non inclusive range but due to the facts that it was used much
it didn't cause trouble.
Another thing I found in kvm_zap_gfn_range:
kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
But kvm_flush_remote_tlbs_with_address expects (struct kvm *kvm, u64 start_gfn, u64 pages)
kvm_flush_remote_tlbs_with_address is also for some reason called twice with the same parameters.
Could you help with that? Am I missing something?
Thanks in advance,
Best regards,
Maxim Levitsky
> Also, checking "activate" is a bit ugly when we have "new" available as
> well. Yes, they are the same if !!old != !!new, but we care about the
> global state, not the single bit.
>
> Putting everything together, this could become something like
>
> trace_kvm_apicv_update_request(activate, bit);
> if (!!old != !!new) {
> /*
> * Kick all CPUs out of guest mode. When
> * kvm_vcpu_update_apicv succeeds in taking
> * apicv_update_lock, it will see the
> * new apicv_inhibit_reasons that we set below.
> */
> kvm_make_all_cpus_request(kvm, KVM_REQ_APICV_UPDATE);
>
> if (new) {
> unsigned long gfn = gpa_to_gfn(APIC_DEFAULT_PHYS_BASE);
> kvm_zap_gfn_range(kvm, gfn, gfn);
> }
> }
> kvm->arch.apicv_inhibit_reasons = new;
> mutex_unlock(&kvm->arch.apicv_update_lock);
>
> Paolo
>
next prev parent reply other threads:[~2021-08-09 18:51 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-02 18:33 [PATCH v3 00/12] My AVIC patch queue Maxim Levitsky
2021-08-02 18:33 ` [PATCH v3 01/12] Revert "KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock" Maxim Levitsky
2021-08-03 8:05 ` Paolo Bonzini
2021-08-03 15:11 ` Sean Christopherson
2021-08-03 17:29 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 02/12] KVM: x86/mmu: bump mmu notifier count in kvm_zap_gfn_range Maxim Levitsky
2021-08-03 9:00 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 03/12] KVM: x86/mmu: rename try_async_pf to kvm_faultin_pfn Maxim Levitsky
2021-08-03 9:00 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 04/12] KVM: x86/mmu: allow kvm_faultin_pfn to return page fault handling code Maxim Levitsky
2021-08-03 9:00 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 05/12] KVM: x86/mmu: allow APICv memslot to be partially enabled Maxim Levitsky
2021-08-03 9:12 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 06/12] KVM: x86: don't disable APICv memslot when inhibited Maxim Levitsky
2021-08-03 8:44 ` Paolo Bonzini
2021-08-09 18:51 ` Maxim Levitsky [this message]
2021-08-09 19:14 ` Sean Christopherson
2021-08-02 18:33 ` [PATCH v3 07/12] KVM: x86: APICv: fix race in kvm_request_apicv_update on SVM Maxim Levitsky
2021-08-02 18:33 ` [PATCH v3 08/12] KVM: SVM: add warning for mistmatch between AVIC state and AVIC access page state Maxim Levitsky
2021-08-03 8:45 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 09/12] KVM: x86: hyper-v: Deactivate APICv only when AutoEOI feature is in use Maxim Levitsky
2021-08-03 8:47 ` Paolo Bonzini
2021-08-03 9:01 ` Paolo Bonzini
2021-08-03 9:11 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 10/12] KVM: SVM: remove svm_toggle_avic_for_irq_window Maxim Levitsky
2021-08-03 9:11 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 11/12] KVM: SVM: call avic_vcpu_load/avic_vcpu_put when enabling/disabling AVIC Maxim Levitsky
2021-08-03 9:00 ` Paolo Bonzini
2021-08-02 18:33 ` [PATCH v3 12/12] KVM: SVM: AVIC: drop unsupported AVIC base relocation code Maxim Levitsky
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