From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Cc: pbonzini@redhat.com, joro@8bytes.org, bp@alien8.de,
gleb@kernel.org, alex.williamson@redhat.com, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, wei@redhat.com,
sherry.hurwitz@amd.com
Subject: Re: [PART1 RFC v4 09/11] svm: Do not expose x2APIC when enable AVIC
Date: Mon, 11 Apr 2016 22:54:24 +0200 [thread overview]
Message-ID: <20160411205423.GA29328@potion.brq.redhat.com> (raw)
In-Reply-To: <1460017232-17429-10-git-send-email-Suravee.Suthikulpanit@amd.com>
2016-04-07 03:20-0500, Suravee Suthikulpanit:
> From: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
>
> Since AVIC only virtualizes xAPIC hardware for the guest, this patch
> disable x2APIC support in guest CPUID.
>
> Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
> ---
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> @@ -4560,14 +4560,26 @@ static u64 svm_get_mt_mask(struct kvm_vcpu *vcpu, gfn_t gfn, bool is_mmio)
> static void svm_cpuid_update(struct kvm_vcpu *vcpu)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> + struct kvm_cpuid_entry2 *entry;
>
> /* Update nrips enabled cache */
> svm->nrips_enabled = !!guest_cpuid_has_nrips(&svm->vcpu);
> +
> + if (!svm_vcpu_avic_enabled(svm))
> + return;
> +
> + entry = kvm_find_cpuid_entry(vcpu, 0x1, 0);
> + if (entry->function == 1)
entry->function == 1 will always be true, because entry can be NULL
otherwise, so we would bug before. Check for entry.
> + entry->ecx &= ~bit(X86_FEATURE_X2APIC);
> }
>
> static void svm_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
> {
> switch (func) {
> + case 0x00000001:
("case 1:" or "case 0x1:" would be easier to read.)
> + if (avic)
> + entry->ecx &= ~bit(X86_FEATURE_X2APIC);
> + break;
---
A rant for the unlikely case I get back to fix the broader situation:
Only one of these two additions is needed. If we do the second one,
then userspace should not set X2APIC, therefore the first one is
useless.
Omitting the second one allows userspace to clear apicv_active and set
X86_FEATURE_X2APIC, but it needs a non-intuitive order of ioctls, so I
think we should have the second one.
The problem is that KVM doesn't seems to check whether userspace sets
cpuid that is a subset of supported ones, so omitting the first one
needlessly expands the space for potential failures.
next prev parent reply other threads:[~2016-04-11 20:54 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-07 8:20 [PART1 RFC v4 00/11] KVM: x86: Introduce SVM AVIC support Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 01/11] KVM: x86: Misc LAPIC changes to expose helper functions Suravee Suthikulpanit
2016-04-11 20:34 ` Radim Krčmář
2016-04-18 19:57 ` Suravee Suthikulpanit
2016-04-18 20:29 ` Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 02/11] KVM: x86: Introducing kvm_x86_ops VM init/uninit hooks Suravee Suthikulpanit
2016-04-11 20:49 ` Radim Krčmář
2016-04-12 21:55 ` Paolo Bonzini
2016-04-18 22:01 ` Suravee Suthikulpanit
2016-04-18 20:40 ` Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 03/11] KVM: x86: Introducing kvm_x86_ops VCPU blocking/unblocking hooks Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 04/11] KVM: split kvm_vcpu_wake_up from kvm_vcpu_kick Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 05/11] svm: Introduce new AVIC VMCB registers Suravee Suthikulpanit
2016-04-07 8:20 ` [PART1 RFC v4 06/11] KVM: x86: Detect and Initialize AVIC support Suravee Suthikulpanit
2016-04-11 20:48 ` Radim Krčmář
2016-04-12 21:54 ` Paolo Bonzini
2016-04-07 8:20 ` [PART1 RFC v4 07/11] svm: Add interrupt injection via AVIC Suravee Suthikulpanit
2016-04-11 20:52 ` Radim Krčmář
2016-04-07 8:20 ` [PART1 RFC v4 08/11] svm: Add VMEXIT handlers for AVIC Suravee Suthikulpanit
2016-04-12 16:22 ` Radim Krčmář
2016-04-12 22:29 ` Paolo Bonzini
2016-04-13 12:37 ` Radim Krčmář
2016-04-28 22:08 ` Suravee Suthikulanit
2016-04-29 14:56 ` Radim Krčmář
2016-04-07 8:20 ` [PART1 RFC v4 09/11] svm: Do not expose x2APIC when enable AVIC Suravee Suthikulpanit
2016-04-11 20:54 ` Radim Krčmář [this message]
2016-04-12 22:09 ` Paolo Bonzini
2016-04-07 8:20 ` [PART1 RFC v4 10/11] svm: Do not intercept CR8 " Suravee Suthikulpanit
2016-04-12 14:18 ` Radim Krčmář
2016-04-12 22:26 ` Paolo Bonzini
2016-04-07 8:20 ` [PART1 RFC v4 11/11] svm: Manage vcpu load/unload " Suravee Suthikulpanit
2016-04-12 14:34 ` Radim Krčmář
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