On Thu, 2021-05-06 at 10:32 +0000, ilstam@xxxxxxxxxxx wrote:
> From: Ilias Stamatis <ilstam@xxxxxxxxxx>
>
> Calculating the current TSC offset is done differently when nested TSC
> scaling is used.
>
> Signed-off-by: Ilias Stamatis <ilstam@xxxxxxxxxx>
> ---
> arch/x86/kvm/vmx/vmx.c | 26 ++++++++++++++++++++------
> 1 file changed, 20 insertions(+), 6 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 49241423b854..df7dc0e4c903 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1797,10 +1797,16 @@ static void setup_msrs(struct vcpu_vmx *vmx)
> vmx_update_msr_bitmap(&vmx->vcpu);
> }
>
> -static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> +/*
> + * This function receives the requested offset for L1 as an argument but it
> + * actually writes the "current" tsc offset to the VMCS and returns it. The
> + * current offset might be different in case an L2 guest is currently running
> + * and its VMCS02 is loaded.
> + */
(Not related to this patch) It might be a good idea to rename this callback
instead of this comment, but I am not sure about it.
> +static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 l1_offset)
> {
> struct vmcs12 *vmcs12 = get_vmcs12(vcpu);
> - u64 g_tsc_offset = 0;
> + u64 cur_offset = l1_offset;
>
> /*
> * We're here if L1 chose not to trap WRMSR to TSC. According
> @@ -1809,11 +1815,19 @@ static u64 vmx_write_l1_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> * to the newly set TSC to get L2's TSC.
> */
> if (is_guest_mode(vcpu) &&
> - (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETTING))
> - g_tsc_offset = vmcs12->tsc_offset;
> + (vmcs12->cpu_based_vm_exec_control & CPU_BASED_USE_TSC_OFFSETTING)) {
> + if (vmcs12->secondary_vm_exec_control & SECONDARY_EXEC_TSC_SCALING) {
> + cur_offset = kvm_compute_02_tsc_offset(
> + l1_offset,
> + vmcs12->tsc_multiplier,
> + vmcs12->tsc_offset);
> + } else {
> + cur_offset = l1_offset + vmcs12->tsc_offset;
> + }
> + }
>
> - vmcs_write64(TSC_OFFSET, offset + g_tsc_offset);
> - return offset + g_tsc_offset;
> + vmcs_write64(TSC_OFFSET, cur_offset);
> + return cur_offset;
> }
>
> /*
This code would be ideal to move to common code as SVM will do basically
the same thing.
Doesn't have to be done now though.
Best regards,
Maxim Levitsky
