On Thu, Mar 07, 2013 at 02:08:07PM +0100, Jan Kiszka wrote:
> The logic for calculating the value with which we call kvm_set_cr0/4 was
> broken (will definitely be visible with nested unrestricted guest mode
> support). Also, we performed the check regarding CR0_ALWAYSON too early
> when in guest mode.
>
> What really needs to be done on both CR0 and CR4 is to mask out L1-owned
> bits and merge them in from L1's guest_cr0/4. In contrast, arch.cr0/4
> and arch.cr0/4_guest_owned_bits contain the mangled L0+L1 state and,
> thus, are not suited as input.
>
> For both CRs, we can then apply the check against VMXON_CRx_ALWAYSON and
> refuse the update if it fails. To be fully consistent, we implement this
> check now also for CR4. For CR4, we move the check into vmx_set_cr4
> while we keep it in handle_set_cr0. This is because the CR0 checks for
> vmxon vs. guest mode will diverge soon when adding unrestricted guest
> mode support.
>
> Finally, we have to set the shadow to the value L2 wanted to write
> originally.
>
> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Reviewed-by: Gleb Natapov <gleb@xxxxxxxxxx>
> ---
>
> Changes in v3:
> - build input for kvm_set_cr0/4 from vmcs12->guest_cr0/4
> - extended comment
> - move CR4 checks to vmx_set_cr4
>
> arch/x86/kvm/vmx.c | 48 +++++++++++++++++++++++++++++++++---------------
> 1 files changed, 33 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index a9d8853..260da9a 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3223,7 +3223,9 @@ static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> */
> if (!nested_vmx_allowed(vcpu))
> return 1;
> - } else if (to_vmx(vcpu)->nested.vmxon)
> + }
> + if (to_vmx(vcpu)->nested.vmxon &&
> + ((cr4 & VMXON_CR4_ALWAYSON) != VMXON_CR4_ALWAYSON))
> return 1;
>
> vcpu->arch.cr4 = cr4;
> @@ -4612,34 +4614,50 @@ vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
> /* called to set cr0 as appropriate for a mov-to-cr0 exit. */
> static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
> {
> - if (to_vmx(vcpu)->nested.vmxon &&
> - ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
> - return 1;
> -
> if (is_guest_mode(vcpu)) {
> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + unsigned long orig_val = val;
> +
> /*
> * We get here when L2 changed cr0 in a way that did not change
> * any of L1's shadowed bits (see nested_vmx_exit_handled_cr),
> - * but did change L0 shadowed bits. This can currently happen
> - * with the TS bit: L0 may want to leave TS on (for lazy fpu
> - * loading) while pretending to allow the guest to change it.
> + * but did change L0 shadowed bits. So we first calculate the
> + * effective cr0 value that L1 would like to write into the
> + * hardware. It consists of the L2-owned bits from the new
> + * value combined with the L1-owned bits from L1's guest_cr0.
> */
> - if (kvm_set_cr0(vcpu, (val & vcpu->arch.cr0_guest_owned_bits) |
> - (vcpu->arch.cr0 & ~vcpu->arch.cr0_guest_owned_bits)))
> + val = (val & ~vmcs12->cr0_guest_host_mask) |
> + (vmcs12->guest_cr0 & vmcs12->cr0_guest_host_mask);
> +
> + /* TODO: will have to take unrestricted guest mode into
> + * account */
> + if ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON)
> return 1;
> - vmcs_writel(CR0_READ_SHADOW, val);
> +
> + if (kvm_set_cr0(vcpu, val))
> + return 1;
> + vmcs_writel(CR0_READ_SHADOW, orig_val);
> return 0;
> - } else
> + } else {
> + if (to_vmx(vcpu)->nested.vmxon &&
> + ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
> + return 1;
> return kvm_set_cr0(vcpu, val);
> + }
> }
>
> static int handle_set_cr4(struct kvm_vcpu *vcpu, unsigned long val)
> {
> if (is_guest_mode(vcpu)) {
> - if (kvm_set_cr4(vcpu, (val & vcpu->arch.cr4_guest_owned_bits) |
> - (vcpu->arch.cr4 & ~vcpu->arch.cr4_guest_owned_bits)))
> + struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> + unsigned long orig_val = val;
> +
> + /* analogously to handle_set_cr0 */
> + val = (val & ~vmcs12->cr4_guest_host_mask) |
> + (vmcs12->guest_cr4 & vmcs12->cr4_guest_host_mask);
> + if (kvm_set_cr4(vcpu, val))
> return 1;
> - vmcs_writel(CR4_READ_SHADOW, val);
> + vmcs_writel(CR4_READ_SHADOW, orig_val);
> return 0;
> } else
> return kvm_set_cr4(vcpu, val);
> --
> 1.7.3.4
--
Gleb.
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