gregkh@linuxfoundation.org writes:
The patch below does not apply to the 5.16-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
I'll do the backporting.
Side note: there's (at least) one more fix needed in the area for SGX enabled CPUs:
https://lore.kernel.org/kvm/20220121132852.2482355-3-vkuznets@redhat.com/ ("No functional change intended" doesn't apply anymore as the order has changed). Hope it'll make upstream (Cc: stable) in the next rc.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From c6617c61e8fe44b9e9fdfede921f61cac6b5149d Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov vkuznets@redhat.com Date: Mon, 17 Jan 2022 16:05:40 +0100 Subject: [PATCH] KVM: x86: Partially allow KVM_SET_CPUID{,2} after KVM_RUN
Commit feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") forbade changing CPUID altogether but unfortunately this is not fully compatible with existing VMMs. In particular, QEMU reuses vCPU fds for CPU hotplug after unplug and it calls KVM_SET_CPUID2. Instead of full ban, check whether the supplied CPUID data is equal to what was previously set.
Reported-by: Igor Mammedov imammedo@redhat.com Fixes: feb627e8d6f6 ("KVM: x86: Forbid KVM_SET_CPUID{,2} after KVM_RUN") Signed-off-by: Vitaly Kuznetsov vkuznets@redhat.com Message-Id: 20220117150542.2176196-3-vkuznets@redhat.com Cc: stable@vger.kernel.org [Do not call kvm_find_cpuid_entry repeatedly. - Paolo] Signed-off-by: Paolo Bonzini pbonzini@redhat.com
diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c index 812190a707f6..7eb046d907c6 100644 --- a/arch/x86/kvm/cpuid.c +++ b/arch/x86/kvm/cpuid.c @@ -119,6 +119,28 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu, return fpu_enable_guest_xfd_features(&vcpu->arch.guest_fpu, xfeatures); } +/* Check whether the supplied CPUID data is equal to what is already set for the vCPU. */ +static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
int nent)
+{
- struct kvm_cpuid_entry2 *orig;
- int i;
- if (nent != vcpu->arch.cpuid_nent)
return -EINVAL;
- for (i = 0; i < nent; i++) {
orig = &vcpu->arch.cpuid_entries[i];
if (e2[i].function != orig->function ||
e2[i].index != orig->index ||
e2[i].eax != orig->eax || e2[i].ebx != orig->ebx ||
e2[i].ecx != orig->ecx || e2[i].edx != orig->edx)
return -EINVAL;
- }
- return 0;
+}
static void kvm_update_kvm_cpuid_base(struct kvm_vcpu *vcpu) { u32 function; @@ -313,6 +335,20 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2, __kvm_update_cpuid_runtime(vcpu, e2, nent);
- /*
* KVM does not correctly handle changing guest CPUID after KVM_RUN, as
* MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't
* tracked in kvm_mmu_page_role. As a result, KVM may miss guest page
* faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with
* the core vCPU model on the fly. It would've been better to forbid any
* KVM_SET_CPUID{,2} calls after KVM_RUN altogether but unfortunately
* some VMMs (e.g. QEMU) reuse vCPU fds for CPU hotplug/unplug and do
* KVM_SET_CPUID{,2} again. To support this legacy behavior, check
* whether the supplied CPUID data is equal to what's already set.
*/
- if (vcpu->arch.last_vmentry_cpu != -1)
return kvm_cpuid_check_equal(vcpu, e2, nent);
- r = kvm_check_cpuid(vcpu, e2, nent); if (r) return r;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 60da2331ec32..a0bc637348b2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -5230,17 +5230,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, struct kvm_cpuid __user *cpuid_arg = argp; struct kvm_cpuid cpuid;
/*
* KVM does not correctly handle changing guest CPUID after KVM_RUN, as
* MAXPHYADDR, GBPAGES support, AMD reserved bit behavior, etc.. aren't
* tracked in kvm_mmu_page_role. As a result, KVM may miss guest page
* faults due to reusing SPs/SPTEs. In practice no sane VMM mucks with
* the core vCPU model on the fly, so fail.
*/
r = -EINVAL;
if (vcpu->arch.last_vmentry_cpu != -1)
goto out;
- r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out;
@@ -5251,14 +5240,6 @@ long kvm_arch_vcpu_ioctl(struct file *filp, struct kvm_cpuid2 __user *cpuid_arg = argp; struct kvm_cpuid2 cpuid;
/*
* KVM_SET_CPUID{,2} after KVM_RUN is forbidded, see the comment in
* KVM_SET_CPUID case above.
*/
r = -EINVAL;
if (vcpu->arch.last_vmentry_cpu != -1)
goto out;
- r = -EFAULT; if (copy_from_user(&cpuid, cpuid_arg, sizeof(cpuid))) goto out;