diff options
| author | Chao Gao <chao.gao@intel.com> | 2025-10-27 23:01:41 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-11-04 09:14:26 -0800 |
| commit | cab4098be41826a91b55cdc851196d73d7057f9c (patch) | |
| tree | 411adec4b900563b23d5e20a2e0d60b124d356e5 | |
| parent | 9bc610b6a2a71d1a6acac27e82a0bc8ca861c7ac (diff) | |
KVM: x86: Call out MSR_IA32_S_CET is not handled by XSAVES
Update the comment above is_xstate_managed_msr() to note that
MSR_IA32_S_CET isn't saved/restored by XSAVES/XRSTORS.
MSR_IA32_S_CET isn't part of CET_U/S state as the SDM states:
The register state used by Control-Flow Enforcement Technology (CET)
comprises the two 64-bit MSRs (IA32_U_CET and IA32_PL3_SSP) that manage
CET when CPL = 3 (CET_U state); and the three 64-bit MSRs
(IA32_PL0_SSP–IA32_PL2_SSP) that manage CET when CPL < 3 (CET_S state).
Opportunistically shift the snippet about the safety of loading certain
MSRs to the function comment for kvm_access_xstate_msr(), which is where
the MSRs are actually loaded into hardware.
Fixes: e44eb58334bb ("KVM: x86: Load guest FPU state when access XSAVE-managed MSRs")
Signed-off-by: Chao Gao <chao.gao@intel.com>
Link: https://patch.msgid.link/20251028060142.29830-1-chao.gao@intel.com
[sean: shift snippet about safety to kvm_access_xstate_msr()]
Signed-off-by: Sean Christopherson <seanjc@google.com>
| -rw-r--r-- | arch/x86/kvm/x86.c | 17 |
1 files changed, 8 insertions, 9 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 67e5f735adf2..c9c2aa6f4705 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3874,15 +3874,9 @@ static void record_steal_time(struct kvm_vcpu *vcpu) /* * Returns true if the MSR in question is managed via XSTATE, i.e. is context - * switched with the rest of guest FPU state. Note! S_CET is _not_ context - * switched via XSTATE even though it _is_ saved/restored via XSAVES/XRSTORS. - * Because S_CET is loaded on VM-Enter and VM-Exit via dedicated VMCS fields, - * the value saved/restored via XSTATE is always the host's value. That detail - * is _extremely_ important, as the guest's S_CET must _never_ be resident in - * hardware while executing in the host. Loading guest values for U_CET and - * PL[0-3]_SSP while executing in the kernel is safe, as U_CET is specific to - * userspace, and PL[0-3]_SSP are only consumed when transitioning to lower - * privilege levels, i.e. are effectively only consumed by userspace as well. + * switched with the rest of guest FPU state. + * + * Note, S_CET is _not_ saved/restored via XSAVES/XRSTORS. */ static bool is_xstate_managed_msr(struct kvm_vcpu *vcpu, u32 msr) { @@ -3905,6 +3899,11 @@ static bool is_xstate_managed_msr(struct kvm_vcpu *vcpu, u32 msr) * MSR that is managed via XSTATE. Note, the caller is responsible for doing * the initial FPU load, this helper only ensures that guest state is resident * in hardware (the kernel can load its FPU state in IRQ context). + * + * Note, loading guest values for U_CET and PL[0-3]_SSP while executing in the + * kernel is safe, as U_CET is specific to userspace, and PL[0-3]_SSP are only + * consumed when transitioning to lower privilege levels, i.e. are effectively + * only consumed by userspace as well. */ static __always_inline void kvm_access_xstate_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info, |