From: Avi Kivity 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 Signed-off-by: Andrew Morton --- drivers/kvm/kvm.h | 4 +++- drivers/kvm/kvm_main.c | 6 ++++-- 2 files changed, 7 insertions(+), 3 deletions(-) diff -puN drivers/kvm/kvm.h~kvm-workaround-cr0cd-cache-disable-bit-leak-from-guest-to drivers/kvm/kvm.h --- a/drivers/kvm/kvm.h~kvm-workaround-cr0cd-cache-disable-bit-leak-from-guest-to +++ a/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) diff -puN drivers/kvm/kvm_main.c~kvm-workaround-cr0cd-cache-disable-bit-leak-from-guest-to drivers/kvm/kvm_main.c --- a/drivers/kvm/kvm_main.c~kvm-workaround-cr0cd-cache-disable-bit-leak-from-guest-to +++ a/drivers/kvm/kvm_main.c @@ -871,7 +871,8 @@ 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, @@ -1955,7 +1956,8 @@ 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); _