KVM_CAP_DISABLE_QUIRKS is irrevocably broken. The capability does not
advertise the set of quirks which may be disabled to userspace, so it is
impossible to predict the behavior of KVM. Worse yet,
KVM_CAP_DISABLE_QUIRKS will tolerate any value for cap->args[0], meaning
it fails to reject attempts to set invalid quirk bits.
The only valid workaround for the quirky quirks API is to add a new CAP.
Actually advertise the set of quirks that can be disabled to userspace
so it can predict KVM's behavior. Reject values for cap->args[0] that
contain invalid bits.
Finally, add documentation for the new capability and describe the
existing quirks.
Signed-off-by: Oliver Upton <oupton@xxxxxxxxxx>
---
This patch applies cleanly to 5.17-rc5. I am working on
another series that introduces yet another KVM quirk [1], but wanted to
send this patch out ahead of reworking that series.
Should we introduce another quirk, KVM_X86_QUIRK_QUIRKY_DISABLE_QUIRKS,
that provides the new ABI to the old quirks capability? :-P
Documentation/virt/kvm/api.rst | 51 +++++++++++++++++++++++++++++++++
arch/x86/include/asm/kvm_host.h | 7 +++++
arch/x86/kvm/x86.c | 8 ++++++
include/uapi/linux/kvm.h | 1 +
4 files changed, 67 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index a4267104db50..bad9e54cbb68 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6997,6 +6997,57 @@ indicated by the fd to the VM this is called on.
This is intended to support intra-host migration of VMs between userspace VMMs,
upgrading the VMM process without interrupting the guest.
+7.30 KVM_CAP_DISABLE_QUIRKS2
+----------------------------
+
+:Capability: KVM_CAP_DISABLE_QUIRKS2
+:Parameters: args[0] - set of KVM quirks to disable
+:Architectures: x86
+:Type: vm
+
+This capability, if enabled, will cause KVM to disable some behavior
+quirks.
+
+Calling KVM_CHECK_EXTENSION for this capability returns a bitmask of
+quirks that can be disabled in KVM.
+
+The argument to KVM_ENABLE_CAP for this capability is a bitmask of
+quirks to disable, and must be a subset of the bitmask returned by
+KVM_CHECK_EXTENSION.
+
+The valid bits in cap.args[0] are:
+
+=================================== ============================================
+ KVM_X86_QUIRK_LINT0_ENABLED By default, the reset value for the LVT
+ LINT0 register is 0x700 (APIC_MODE_EXTINT).
+ When this quirk is disabled, the reset value
+ is 0x10000 (APIC_LVT_MASKED).
+
+ KVM_X86_QUIRK_CD_NW_CLEARED By default, KVM clears CR0.CD and CR0.NW.
+ When this quirk is disabled, KVM does not
+ change the value of CR0.CD and CR0.NW.
+
+ KVM_X86_QUIRK_LAPIC_MMIO_HOLE By default, the MMIO LAPIC interface is
+ available even when configured for x2APIC
+ mode. When this quirk is disabled, KVM
+ disables the MMIO LAPIC interface if the
+ LAPIC is in x2APIC mode.
+
+ KVM_X86_QUIRK_OUT_7E_INC_RIP By default, KVM pre-increments %rip before
+ exiting to userspace for an OUT instruction
+ to port 0x7e. When this quirk is disabled,
+ KVM does not pre-increment %rip before
+ exiting to userspace.
+
+ KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT When this quirk is disabled, KVM sets
+ CPUID.01H:ECX[bit 3] (MONITOR/MWAIT) if
+ IA32_MISC_ENABLE[bit 18] (MWAIT) is set.
+ Additionally, when this quirk is disabled,
+ KVM clears CPUID.01H:ECX[bit 3] if
+ IA32_MISC_ENABLE[bit 18] is cleared.
+=================================== ============================================
+
+
8. Other capabilities.
======================
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 6dcccb304775..4f01eb977338 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1955,4 +1955,11 @@ int memslot_rmap_alloc(struct kvm_memory_slot *slot, unsigned long npages);
#define KVM_CLOCK_VALID_FLAGS \
(KVM_CLOCK_TSC_STABLE | KVM_CLOCK_REALTIME | KVM_CLOCK_HOST_TSC)
+#define KVM_X86_VALID_QUIRKS \
+ (KVM_X86_QUIRK_LINT0_REENABLED | \
+ KVM_X86_QUIRK_CD_NW_CLEARED | \
+ KVM_X86_QUIRK_LAPIC_MMIO_HOLE | \
+ KVM_X86_QUIRK_OUT_7E_INC_RIP | \
+ KVM_X86_QUIRK_MISC_ENABLE_NO_MWAIT)
+
#endif /* _ASM_X86_KVM_HOST_H */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 641044db415d..e5227aca9e7e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4331,6 +4331,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
r = sizeof(struct kvm_xsave);
break;
}
+ case KVM_CAP_DISABLE_QUIRKS2:
+ r = KVM_X86_VALID_QUIRKS;
+ break;
default:
break;
}
@@ -5877,6 +5880,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
return -EINVAL;
switch (cap->cap) {
+ case KVM_CAP_DISABLE_QUIRKS2:
+ r = -EINVAL;
+ if (cap->args[0] & ~KVM_X86_VALID_QUIRKS)
+ break;
+ fallthrough;
case KVM_CAP_DISABLE_QUIRKS:
kvm->arch.disabled_quirks = cap->args[0];
r = 0;
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5191b57e1562..9f7410496b36 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -1134,6 +1134,7 @@ struct kvm_ppc_resize_hpt {
#define KVM_CAP_VM_GPA_BITS 207
#define KVM_CAP_XSAVE2 208
#define KVM_CAP_SYS_ATTRIBUTES 209
+#define KVM_CAP_DISABLE_QUIRKS2 210
#ifdef KVM_CAP_IRQ_ROUTING
--
2.35.1.574.g5d30c73bfb-goog
