2017-09-22 13:53 GMT+08:00 Ladi Prosek <lprosek@xxxxxxxxxx>:
> For nested virt we maintain multiple VMCS that can run on a vCPU. So it is
> incorrect to keep vmcs_host_cr3 and vmcs_host_cr4, whose purpose is caching
> the value of the rarely changing HOST_CR3 and HOST_CR4 VMCS fields, in
> vCPU-wide data structures.
>
> Hyper-V nested on KVM runs into this consistently for me with PCID enabled.
> CR3 is updated with a new value, unlikely(cr3 != vmx->host_state.vmcs_host_cr3)
> fires, and the currently loaded VMCS is updated. Then we switch from L2 to
> L1 and the next exit reverts CR3 to its old value.
Could you explain why CR3 is updated when PCID is enabled? In
addition, the host cr3/cr4 of both vmcs01 and vmcs02 should be from
the L0, so why there is a difference?
Regards,
Wanpeng Li
>
> Fixes: d6e41f1151fe ("x86/mm, KVM: Teach KVM's VMX code that CR3 isn't a constant")
> Signed-off-by: Ladi Prosek <lprosek@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 0726ca7a1b02..c83d28b0ab05 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -200,6 +200,8 @@ struct loaded_vmcs {
> int cpu;
> bool launched;
> bool nmi_known_unmasked;
> + unsigned long vmcs_host_cr3; /* May not match real cr3 */
> + unsigned long vmcs_host_cr4; /* May not match real cr4 */
> struct list_head loaded_vmcss_on_cpu_link;
> };
>
> @@ -600,8 +602,6 @@ struct vcpu_vmx {
> int gs_ldt_reload_needed;
> int fs_reload_needed;
> u64 msr_host_bndcfgs;
> - unsigned long vmcs_host_cr3; /* May not match real cr3 */
> - unsigned long vmcs_host_cr4; /* May not match real cr4 */
> } host_state;
> struct {
> int vm86_active;
> @@ -5178,12 +5178,12 @@ static void vmx_set_constant_host_state(struct vcpu_vmx *vmx)
> */
> cr3 = __read_cr3();
> vmcs_writel(HOST_CR3, cr3); /* 22.2.3 FIXME: shadow tables */
> - vmx->host_state.vmcs_host_cr3 = cr3;
> + vmx->loaded_vmcs->vmcs_host_cr3 = cr3;
>
> /* Save the most likely value for this task's CR4 in the VMCS. */
> cr4 = cr4_read_shadow();
> vmcs_writel(HOST_CR4, cr4); /* 22.2.3, 22.2.5 */
> - vmx->host_state.vmcs_host_cr4 = cr4;
> + vmx->loaded_vmcs->vmcs_host_cr4 = cr4;
>
> vmcs_write16(HOST_CS_SELECTOR, __KERNEL_CS); /* 22.2.4 */
> #ifdef CONFIG_X86_64
> @@ -9274,15 +9274,15 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
> vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
>
> cr3 = __get_current_cr3_fast();
> - if (unlikely(cr3 != vmx->host_state.vmcs_host_cr3)) {
> + if (unlikely(cr3 != vmx->loaded_vmcs->vmcs_host_cr3)) {
> vmcs_writel(HOST_CR3, cr3);
> - vmx->host_state.vmcs_host_cr3 = cr3;
> + vmx->loaded_vmcs->vmcs_host_cr3 = cr3;
> }
>
> cr4 = cr4_read_shadow();
> - if (unlikely(cr4 != vmx->host_state.vmcs_host_cr4)) {
> + if (unlikely(cr4 != vmx->loaded_vmcs->vmcs_host_cr4)) {
> vmcs_writel(HOST_CR4, cr4);
> - vmx->host_state.vmcs_host_cr4 = cr4;
> + vmx->loaded_vmcs->vmcs_host_cr4 = cr4;
> }
>
> /* When single-stepping over STI and MOV SS, we must clear the
> --
> 2.13.5
>
