On Core-not-2 processors (or on laptops - not sure what the cause is), the
cache disable bit sometimes leaks from the guest cr0 to the host cr0. This
leaves the host limping along at a snail's pace long after the guest has
left. This might be a bug in the processor or in the smm (system management
mode) bios.
Workaround by giving the guest a virtual cr0.cd (and also cr0.nw for good
measure) and keeping the real bits always clear.
This makes sense even without the bug: the processor cache is a host
resource, not a guest resource, and the guest has no business disabling it.
Signed-off-by: Avi Kivity <[email protected]>
Index: linux-2.6/drivers/kvm/kvm.h
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm.h
+++ linux-2.6/drivers/kvm/kvm.h
@@ -31,8 +31,10 @@
#define CR4_VMXE_MASK (1ULL << 13)
#define KVM_GUEST_CR0_MASK \
+ (CR0_PG_MASK | CR0_PE_MASK | CR0_WP_MASK | CR0_NE_MASK \
+ | CR0_NW_MASK | CR0_CD_MASK)
+#define KVM_VM_CR0_ALWAYS_ON \
(CR0_PG_MASK | CR0_PE_MASK | CR0_WP_MASK | CR0_NE_MASK)
-#define KVM_VM_CR0_ALWAYS_ON KVM_GUEST_CR0_MASK
#define KVM_GUEST_CR4_MASK \
(CR4_PSE_MASK | CR4_PAE_MASK | CR4_PGE_MASK | CR4_VMXE_MASK | CR4_VME_MASK)
Index: linux-2.6/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm_main.c
+++ linux-2.6/drivers/kvm/kvm_main.c
@@ -870,7 +870,8 @@ static void __set_cr0(struct kvm_vcpu *v
#endif
vmcs_writel(CR0_READ_SHADOW, cr0);
- vmcs_writel(GUEST_CR0, cr0 | KVM_VM_CR0_ALWAYS_ON);
+ vmcs_writel(GUEST_CR0,
+ (cr0 & ~KVM_GUEST_CR0_MASK) | KVM_VM_CR0_ALWAYS_ON);
}
static int pdptrs_have_reserved_bits_set(struct kvm_vcpu *vcpu,
@@ -3008,7 +3009,8 @@ static int kvm_dev_ioctl_set_sregs(struc
vcpu->rmode.active = ((sregs->cr0 & CR0_PE_MASK) == 0);
update_exception_bitmap(vcpu);
vmcs_writel(CR0_READ_SHADOW, sregs->cr0);
- vmcs_writel(GUEST_CR0, sregs->cr0 | KVM_VM_CR0_ALWAYS_ON);
+ vmcs_writel(GUEST_CR0,
+ (sregs->cr0 & ~KVM_GUEST_CR0_MASK) | KVM_VM_CR0_ALWAYS_ON);
mmu_reset_needed |= guest_cr4() != sregs->cr4;
__set_cr4(vcpu, sregs->cr4);
-
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