Re: [RFC PATCH 8/9] x86/kvm/vmx: Initialize SPEC_CTRL MASK for RRSBA

Chao Gao
2023-01-15T14:20:23Z

On Sun, Dec 11, 2022 at 12:00:45AM +0800, Zhang Chen wrote:
>VMMs can address mitigations issues in migration pool by applying
>the needed controls whenever the guest is operating on a newer
>processor. If a guest is using retpoline to mitigate intra-mode BTI
>in CPL0, the VMM can set RRSBA_DIS_S when the guest runs on hardware
>which enumerates RRSBA.
>
>Signed-off-by: Zhang Chen <chen.zhang@intel.com>
>---
> arch/x86/kvm/vmx/vmx.c | 57 +++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 56 insertions(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index 6ed6b743be0e..fb0f3b1639b9 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -2007,6 +2007,20 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> return 1;
> msr_info->data = vmx->msr_virtual_enumeration;
> break;
>+ case MSR_VIRTUAL_MITIGATION_ENUM:
>+ if (!msr_info->host_initiated &&
>+ !(vmx->msr_virtual_enumeration &
>+ VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+ return 1;
>+ msr_info->data = vmx->msr_virtual_mitigation_enum;
>+ break;
>+ case MSR_VIRTUAL_MITIGATION_CTRL:
>+ if (!msr_info->host_initiated &&
>+ !(vmx->msr_virtual_enumeration &
>+ VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+ return 1;
>+ msr_info->data = vmx->msr_virtual_mitigation_ctrl;
>+ break;
> default:
> find_uret_msr:
> msr = vmx_find_uret_msr(vmx, msr_info->index);
>@@ -2056,7 +2070,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> struct vmx_uret_msr *msr;
> int ret = 0;
> u32 msr_index = msr_info->index;
>- u64 data = msr_info->data;
>+ u64 data = msr_info->data, arch_msr;
> u32 index;
>
> switch (msr_index) {
>@@ -2390,6 +2404,46 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> vmx->msr_virtual_enumeration = data &
> VIRT_ENUM_MITIGATION_CTRL_SUPPORT;
> break;
>+ case MSR_VIRTUAL_MITIGATION_ENUM:
>+ if (msr_info->host_initiated &&
>+ !(vmx->msr_virtual_enumeration &
>+ VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+ return 1;
>+ if (data & ~MITI_ENUM_SUPPORTED)
>+ return 1;
>+ vmx->msr_virtual_mitigation_enum = data;
>+ break;
>+ case MSR_VIRTUAL_MITIGATION_CTRL:
>+ if (!msr_info->host_initiated &&
>+ !(vmx->msr_virtual_enumeration &
>+ VIRT_ENUM_MITIGATION_CTRL_SUPPORT))
>+ return 1;
>+ if (data & ~MITI_CTRL_USED)
>+ return 1;
>+

>+ if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
>+ rdmsrl(MSR_IA32_ARCH_CAPABILITIES, arch_msr);
>+
>+ if (data & MITI_CTRL_RETPOLINE_S_USED &&
>+ boot_cpu_has(X86_FEATURE_RRSBA_CTRL) &&
>+ arch_msr & ARCH_CAP_RRSBA)
>+ vmx->spec_ctrl_mask |= SPEC_CTRL_RRSBA_DIS_S;
>+ else
>+ vmx->spec_ctrl_mask &= ~SPEC_CTRL_RRSBA_DIS_S;

IIUC, only above chunk belongs to this patch. Other changes should be moved
to patch 7, which deals with MSRs emulation.